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1 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu How to Use This Presentation To View the presentation as a slideshow with effects select “View” on the menu bar and click on “Slide Show.” To advance through the presentation, click the right-arrow key or the space bar. From the resources slide, click on any resource to see a presentation for that resource. From the Chapter menu screen click on any lesson to go directly to that lesson’s presentation. You may exit the slide show at any time by pressing the Esc key.

2 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter Presentation Transparencies Bellringer Standardized Test PrepVisual Concepts Sample Problems Resources

3 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Table of Contents Atoms and Moles Section 1 Substances Are Made of Atoms Section 2 Structure of Atoms Section 3 Electron Configuration Section 4 Counting Atoms Chapter 3

4 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Bellringer Make a list of inferences about any properties of objects in the box. How could you learn more about the objects in the box without opening the box? Scientist face these same questions as they try to learn more about atoms. Chapter 3 Section 1 Substances Are Made of Atoms

5 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Objectives State the three laws that support the existence of atoms. List the five principles of John Dalton’s atomic theory. Chapter 3 Section 1 Substances Are Made of Atoms

6 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Theory The idea of an atomic theory is more than 2000 years old. Chapter 3 Section 1 Substances Are Made of Atoms Aristotle Aristotle modified an earlier theory that matter was made of four “elements”: earth, fire, water, air.

7 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Democritus Democritus (430-370 BC), a Greek philosopher, believed that all Matter consists of very small, indivisible particles. He called these particles atomos (Greek for “uncuttable” or “indivisible”). Democritus’ idea, supported by experimental evidence nearly 2500 years later, laid the foundations for our modern understanding of the nature of elements and compounds.

8 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Until recently, scientists had never seen evidence of atoms. The law of definite proportions, the law of conservation of mass and the law of multiple proportions support the current atomic theory.

9 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Theory, continued Chapter 3 Section 1 Substances Are Made of Atoms The figure on the right is a more accurate representation of an atom than the figure on the left.

10 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Theory, continued The Law of Definite Proportions Joseph Proust (1754-1826), in 1799. Proust’s Law of Definite Proportions states: The law of definite proportions states that a chemical compound always contains the same elements in exactly the same proportions by weight or mass. The law of definite proportions also states that every molecule of a substance is made of the same number and types of atoms. Chapter 3 Section 1 Substances Are Made of Atoms

11 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Law of Definite Proportions Chapter 3 PLAY

12 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Theory, continued The Law of Conservation of Mass Law of Conservation of Mass: Antoine Lavoisier consider “the father of modern chemistry” The law of conservation of mass states that mass cannot be created or destroyed in ordinary chemical and physical changes. The mass of the reactants is equal to the mass of the products. Chapter 3 Section 1 Substances Are Made of Atoms

13 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Law of Conservation of Mass Section 1 Substances Are Made of Atoms Chapter 3

14 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Law of Conservation of Mass, continued Section 1 Substances Are Made of Atoms Chapter 3

15 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Law of Conservation of Mass Chapter 3 PLAY

16 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Theory, continued The Law of Multiple Proportions Proposed by John Dalton The law of multiple proportions states that when two elements combine to form two or more compounds, the mass of one element that combines with a given mass of the other is in the ratio of small whole numbers. Chapter 3 Section 1 Substances Are Made of Atoms

17 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Law of Multiple Proportions Section 1 Substances Are Made of Atoms Chapter 3

18 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Law of Multiple Proportions Chapter 3 PLAY

19 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Dalton’s Atomic Theory In 1808, John Dalton developed an atomic theory. Dalton believed that a few kinds of atoms made up all matter. According to Dalton, elements are composed of only one kind of atom and compounds are made from two or more kinds of atoms. Section 1 Substances Are Made of Atoms Chapter 3

20 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Dalton’s Atomic Theory, continued Dalton’s Theory Contains Five Principles 1.All matter is composed of extremely small particles called atoms, which cannot be subdivided, created, or destroyed. 2.Atoms of a given element are identical in their physical and chemical properties. 3.Atoms of different elements differ in their physical and chemical properties. Chapter 3 Section 1 Substances Are Made of Atoms

21 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Dalton’s Atomic Theory, continued Dalton’s Theory Contains Five Principles, continued 4.Atoms of different elements combine in simple, whole-number ratios to form compounds. 5.In chemical reactions, atoms are combined, separated, or rearranged but never created, destroyed, or changed. Data gathered since Dalton’s time shows that the first two principles are not true in all cases. Hwk page 78 Que. 1,2,3,4,5,6 Quiz to Follow Chapter 3 Section 1 Substances Are Made of Atoms

22 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Structure of Atoms Bellringer Look at the following terms: electron, nucleus, proton, neutron, atomic number, mass number, isotope Chapter 3 Sec 2 Video Intro Make a list of the terms that are unfamiliar to you? After completing this section, look over your list to check that you are familiar with and understand all of the terms. Chapter 3

23 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Objectives Describe the evidence for the existence of electrons, protons, neutrons, and describe the properties of these subatomic particles. Discuss atoms of different elements in terms of their numbers of electrons, protons, neutrons, and define the terms atomic number and atomic mass. Define isotope, and determine the number of particles in the nucleus of an isotope. Section 2 Structure of Atoms Chapter 3

24 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Subatomic Particles Experiments by several scientists in the mid-1800s led to the first change to Dalton’s atomic theory. Scientists discovered that atoms can be broken into pieces after all. The smaller parts that make up atoms are called subatomic particles. The three subatomic particles that are most important for chemistry are the electron, the proton, and the neutron. Section 2 Structure of Atoms Chapter 3

25 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Subatomic Particles, continued Electrons Were Discovered Using Cathode Rays To study current, J. J. Thomson pumped most of the air out of a glass tube. He applied a voltage to two metal plates, called electrodes, which were placed at either end of the tube. One electrode, called the anode, was attached to the positive terminal of the voltage source, so it had a positive charge. The other electrode, called a cathode, had a negative charge because it was attached to the negative terminal of the voltage source. Section 2 Structure of Atoms Chapter 3

26 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Subatomic Particles, continued Electrons Were Discovered Using Cathode Rays, continued Thomson observed a glowing beam that came out of the cathode and struck the anode and the nearby glass walls of the tube. He called these rays cathode rays. The glass tube Thomson used is known as a cathode-ray tube (CRT). CRTs are used in television sets, computer monitors, and radar displays. Section 2 Structure of Atoms Chapter 3

27 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Subatomic Particles, continued An Electron Has a Negative Charge Because the cathode ray came from the negatively charged cathode, Thomson reasoned that the ray was negatively charged. Thomson confirmed this prediction by seeing how electric and magnetic fields affected the cathode ray. Thomson also observed that when a small paddle wheel was placed in the path of the rays, the wheel would turn. This suggested that the cathode rays consisted of tiny particles that were hitting the paddles of the wheel. Section 2 Structure of Atoms Chapter 3

28 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Thompson’s Cathode Ray Tube Experiment Chapter 3 PLAY

29 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu United Streaming (Discovery) Search Cathode rays to xrays Program overview VIDEO

30 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Subatomic Particles, continued An Electron Has a Negative Charge, continued Thomson’s experiments showed that a cathode ray consists of particles that have mass and a negative charge. These particles are called electrons. An electron is a subatomic particle that has a negative electric charge. Electrons are negatively charged, but atoms have no charge. Atoms contain some positive charges that balance the negative charges of the electrons. Section 2 Structure of Atoms Chapter 3

31 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Subatomic Particles, continued An Electron Has a Negative Charge, continued Properties of Electrons Section 2 Structure of Atoms Chapter 3

32 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Subatomic Particles, continued Thomson proposed that the electrons of an atom were embedded in a positively charged ball of matter. His model of an atom was named the plum-pudding model. Section 2 Structure of Atoms Chapter 3

33 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Subatomic Particles, continued Rutherford Discovers the Nucleus, continued Ernest Rutherford performed the gold foil experiment, which disproved the plum-pudding model of the atom. Rutherford’s Expt. A beam of small, positively charged particles, called alpha particles, was directed at a thin gold foil. Rutherford’s team measured the angles at which the particles were deflected from their former straight-line paths as they came out of the foil. Rutherford found that most of the alpha particles shot at the foil passed straight through the foil. But very few were deflected, in some cases backward. Section 2 Structure of Atoms Chapter 3

34 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Gold Foil Experiment Chapter 3

35 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Subatomic Particles, continued Rutherford Discovers the Nucleus, continued Rutherford reasoned that only a very concentrated positive charge in a tiny space within the gold atom could possibly repel the fast-moving, alpha particles enough to reverse the alpha particles’ direction. Rutherford also hypothesized that the mass of this positive-charge containing region, called the nucleus, must be larger than the mass of the alpha particle. Rutherford argued that the reason most of the alpha particles were undeflected, was that most parts of the atoms in the gold foil were empty space. Section 2 Structure of Atoms Chapter 3

36 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Gold Foil Experiment on the Atomic Level Chapter 3

37 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Subatomic Particles, continued Rutherford Discovers the Nucleus, continued The nucleus is the dense, central portion of the atom. The nucleus is made up of protons and neutrons. The nucleus has all of the positive charge, nearly all of the mass, but only a very small fraction of the volume of the atom. Section 2 Structure of Atoms Chapter 3

38 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Rutherford’s Gold Foil Experiment Chapter 3 PLAY

39 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Subatomic Particles, continued Proton and Neutrons Compose the Nucleus Protons are the subatomic particles that have a positive charge and that is found in the nucleus of an atom. The number of protons of the nucleus is the atomic number, which determines the identity of an element. Because protons and electrons have equal but opposite charges, a neutral atom must contain equal numbers of protons and electrons. Neutrons are the subatomic particles that have no charge and that is found in the nucleus of an atom. Section 2 Structure of Atoms Chapter 3

40 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Subatomic Particles, continued Proton and Neutrons Compose the Nucleus, continued Properties of a Proton and a Neutron Section 2 Structure of Atoms Chapter 3

41 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu SymbolChargeMassRelative Charge Relative Mass Electrone-e- -1.602 x 10 -19 C 9.109 x 10 -31 kg 1-1 Protonp+p+ +1.602 x10 -19 C 1.673 x 10 -27 kg 1+1837 Neutronn0n0 0 C1.675 x 10 -27 kg 01839

42 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Parts of an Atom Chapter 3 PLAY

43 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Subatomic Particles, continued Protons and Neutrons Can Form a Stable Nucleus Coulomb’s law states that the closer two charges are, the greater the force between them. Section 2 Structure of Atoms Chapter 3 The repulsive force between two protons is large when two protons are close together.

44 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Subatomic Particles, continued Protons and Neutrons Can Form a Stable Nucleus Protons form stable nuclei despite the repulsive force between them. A strong attractive force between these protons overcomes the repulsive force at small distances. Because neutrons also add attractive forces, some neutrons can help stabilize a nucleus. (Act as glue) All atoms that have more than one proton also have neutrons. Section 2 Structure of Atoms Chapter 3

45 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Number and Mass Number Atomic Number Is the Number of Protons of the Nucleus The number of protons that an atom has is known as the atom’s atomic number. The atomic number is the same for all atoms of an element. Because each element has a unique number of protons in its atoms, no two elements have the same atomic number. Example: the atomic number of hydrogen is 1 because the nucleus of each hydrogen atom has one proton. The atomic number of oxygen is 8. Section 2 Structure of Atoms Chapter 3

46 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Number and Mass Number, continued Atomic Number Is the Number of Protons of the Nucleus, continued Atomic numbers are always whole numbers. The atomic number also reveals the number of electrons in an atom of an element. For atoms to be neutral, the number of negatively charged electrons must equal the number of positively charged protons. Section 2 Structure of Atoms Chapter 3

47 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Number and Mass Number, continued Atomic Number Is the Number of Protons of the Nucleus, continued Section 2 Structure of Atoms The atomic number for oxygen tells you that the oxygen atom has 8 protons and 8 electrons. Chapter 3

48 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Atomic Number Chapter 3

49 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Number and Mass Number, continued Mass Number Is the Number of Particles of the Nucleus, continued The mass number is the sum of the number of protons and neutrons in the nucleus of an atom. You can calculate the number of neutrons in an atom by subtracting the atomic number (the number of protons) from the mass number (the number of protons and neutrons). mass number – atomic number = number of neutrons Unlike the atomic number, the mass number can vary among atoms of a single element. Section 2 Structure of Atoms Chapter 3

50 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Number and Mass Number, continued Mass Number Is the Number of Particles of the Nucleus, continued Example: a particular atom of neon has a mass number of 20. Because the atomic number for an atom of neon is 10, neon has 10 protons. number of protons and neutrons (mass number) = 20  number of protons (atomic number) = 10 number of neutrons = 10 Section 2 Structure of Atoms Chapter 3

51 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Number and Mass Number, continued Mass Number Is the Number of Particles of the Nucleus, continued The neon atom has 10 protons, 10 electrons, and 10 neutrons. The mass number is 20. Section 2 Structure of Atoms Chapter 3

52 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Mass Number Chapter 3

53 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Structure of Atoms Determining the Number of Particle In An Atom Sample Problem A How many protons, electrons, and neutrons are present in an atom of copper whose atomic number is 29 and whose mass number is 64? Chapter 3

54 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Structure of Atoms Sample Problem A Solution The atomic number indicates the number of protons in the nucleus of a copper atom. atomic number (29) = number of protons = 29 A copper atom must be electrically neutral, so the number of electrons equals the number of protons. number of protons = number of electrons = 29 The mass number indicates the total number of protons and neutrons mass number (64) - atomic number (29) = number of neutrons = 35 Chapter 3

55 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Number and Mass Number, continued Atomic Structures Can Be Represented by Symbols Each element has a name, and the same name is given to all atoms of an element. Example: sulfur is composed of sulfur atoms. Each element has a symbol, and the same symbol is used to represent one of the element’s atoms. Atomic number and mass number are sometimes written with an element’s symbol. Section 2 Structure of Atoms Chapter 3

56 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Number and Mass Number, continued Isotopes of an Element Have the Same Atomic Number All atoms of an element have the same atomic number and the same number of protons. Atoms do not necessarily have the same number of neutrons. Atoms of the same element that have different numbers of neutrons are called isotopes. One standard method of identifying isotopes is to write the mass number with a hyphen after the name of an element. helium-3 or helium-4 Section 2 Structure of Atoms Chapter 3

57 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Number and Mass Number, continued Atomic Structures Can Be Represented by Symbols A ZXZX Section 2 Structure of Atoms Chapter 3 A is the mass number Z is the atomic number X is the element symbol Ex) 239 92 U orElement Name-Mass Number Uranium-239

58 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Number and Mass Number, continued Atomic Structures Can Be Represented by Symbols The atomic number always appears on the lower left side of the symbol. Section 2 Structure of Atoms Mass numbers are written on the upper left side of the symbol. Chapter 3

59 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Number and Mass Number, continued Atomic Structures Can Be Represented by Symbols Both numbers may be written with the symbol. Section 2 Structure of Atoms An element may be represented by more than one notation. Chapter 3

60 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Number and Mass Number, continued Isotopes of an Element Have the Same Atomic Number, continued The second method of identifying isotopes shows the composition of a nucleus as the isotope’s nuclear symbol. Section 2 Structure of Atoms Chapter 3 All isotopes of an element have the same atomic number. However, their atomic masses are not the same because the number of neutrons of the atomic nucleus of each isotope varies.

61 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Number and Mass Number, continued Isotopes of an Element Have the Same Atomic Number, continued The two stable helium isotopes are helium-3 and helium-4. Section 2 Structure of Atoms Chapter 3

62 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Number and Mass Number, continued Isotopes of an Element Have the Same Atomic Number, continued The Stable Isotopes of Lead Section 2 Structure of Atoms Chapter 3

63 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Isotopes and Nuclides Chapter 3 PLAY

64 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Determining the Number of Particle In An Isotope Sample Problem B Calculate the numbers of protons, electrons, and neutrons in oxygen-17 and in oxygen-18. Chapter 3 Section 2 Structure of Atoms

65 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Sample Problem B Solution atomic number = number of protons = number of electrons = 8 Chapter 3 Section 2 Structure of Atoms mass number - atomic number = number of neutrons For oxygen-17, 17 - 8 = 9 neutrons For oxygen-18, 18 - 8 = 10 neutrons

66 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Ex) 32 16 S Ex)108 47 Ag 2+ Ex)80 35 Br 1- Chapter 3Section 2 Structure of Atoms

67 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Ex) Fluorine-19 Ex) Calcium-44 Ex) Write the symbol that has 34 protons, 34 electrons, and 46 neutrons. Ex) Write the symbol that has 17 protons, 18 electrons, and 17 neutrons. Ex) Write the symbol that has 79 protons, 77 electrons, and 118 neutrons. Chapter 3Section 2 Structure of Atoms

68 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Homework  Worksheet Quiz to Follow

69 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Objectives Compare the Rutherford, Bohr, and quantum models of an atom. Explain how the wavelengths of light emitted by an atom provide information about electron energy levels. List the four quantum numbers, and describe their significance. Write the electron configuration of an atom by using the Pauli exclusion principle and the the aufbau principle. Section 3 Electron Configuration Chapter 3

70 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Evolution of the Atom or Models of the Atom

71 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 1) John Dalton Model  Billard Ball Model

72 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 2) J.J. Thomson Model or Plum Pudding Model 1904 the electrons are like raisins dispersed in a pudding (positive charge cloud) seeds in a watermelon blue-berry muffin

73 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Models Rutherford’s Model Proposed Electron Orbits The experiments of Rutherford’s team led to the replacement of the plum pudding model of the atom with a nuclear model of the atom. Rutherford suggested that electrons, like planets orbiting the sun, revolve around the nucleus in circular or elliptical orbits. Rutherford’s model could not explain why electrons did not crash into the nucleus. The Rutherford model of the atom was replaced only two years later by a model developed by Niels Bohr. Section 3 Electron Configuration Chapter 3

74 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Evolution of the Atom 3) Rutherford Model or Nuclear Atom Model 1911 positive dense center called the nucleus rest of atom empty space (electrons reside)

75 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu

76 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Evolution of the Atom 4) Bohr Model or the Shell Model 1913 pictured the atom as a small positive nucleus with electrons orbiting around it in curved circular pathways

77 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Models, continued Bohr’s Model Confines Electrons to Energy Levels According to Bohr’s model, electrons can be only certain distances from the nucleus. Each distance corresponds to a certain quantity of energy that an electron can have. An electron that is as close to the nucleus as it can be is in its lowest energy level. The farther an electron is from the nucleus, the higher the energy level that the electron occupies. The difference in energy between two energy levels is known as a quantum of energy. Section 3 Electron Configuration Chapter 3

78 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Niels Bohr (Born in Denmark 1885-1962) Student of Rutherford

79 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Niels Bohr’s Model (1913) Electrons orbit the nucleus in circular paths of fixed energy (energy levels).

80 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Max Plank E=h E=energy =frequency h=Plank’s constant 6.7x10 -34 Js

81 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Energy of Emitted Photon Energy of the emitted photon = Difference in energy between two states

82 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Energy emitted by the electron as it leaps from the higher to the lower energy level is proportional to the frequency of the light wave. Frequency define the color of visible light.

83 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Niels Bohr’s Atom Cont’d Electrons can jump from energy level to energy level. Electrons absorb or emit light energy when they jump from one energy level to another.

84 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu A quantum of energy is the amount of energy required to move an electron from one energy level to another. Quantum

85 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The energy levels are like the rungs of a ladder but are not equally spaced.

86 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Photons Photons are bundles of light energy that is emitted by electrons as they go from higher energy levels to lower levels.

87 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Excited State and Ground State Ground state: the lowest possible energy level an electron can be at. Excited state: an energy level higher than the ground state.

88 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu

89 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Emission Spectrum Light emitted produces a unique emission spectrum.

90 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Hydrogen Emission Spectrum Violet Blue Red Balmer Series

91 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Bohr Model for Hydrogen

92 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Bohr model explained the emission spectrum of the hydrogen atom but did not always explain those of other elements.

93 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Evolution of the Atom 5) Wave Mechanical Model or the Electron Cloud Model 1920’s Louis Victor de Broglie and Erwin Schrodinger suggested that because light seems to behave both as a wave and as a stream of particles, then the electron should exhibit both of these characteristics Orbitals (electron states) are nothing like orbits Similar to a cloud or firefly analogy (highest probability) Heisenberg Uncertainty Principle  we will never know simultaneously the exact momentum and position of an electron

94 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Models, continued Electrons Act Like Both Particles and Waves Thomson’s experiments demonstrated that electrons act like particles that have mass. In 1924, Louis de Broglie pointed out that the behavior of electrons according to Bohr’s model was similar to the behavior of waves. De Broglie suggested that electrons could be considered waves confined to the space around a nucleus. As waves, electrons could have only certain frequencies which correspond to the specific energy levels. Section 3 Electron Configuration Chapter 3

95 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts De Broglie and the Wave-Particle Nature of Electrons Chapter 3 PLAY

96 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Models, continued Electrons Act Like Both Particles and Waves, continued The present-day model of the atom takes into account both the particle and wave properties of electrons. In this model, electrons are located in orbitals, regions around a nucleus that correspond to specific energy levels. Orbitals are regions where electrons are likely to be found. Orbitals are sometimes called electron clouds because they do not have sharp boundaries. Because electrons can be in other places, the orbital has a fuzzy boundary like a cloud. Section 3 Electron Configuration Chapter 3

97 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Models, continued Electrons Act Like Both Particles and Waves, continued According to the current model of an atom, electrons are found in orbitals. Section 3 Electron Configuration Chapter 3

98 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Quantum Mechanical Model 1920’s Werner Heisenberg (Uncertainty Principle) Louis de Broglie (electron has wave properties) Erwin Schrodinger (mathematical equations using probability, quantum numbers)

99 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Werner Heisenberg: Uncertainty Principle We can not know both the position and momentum of a particle at a given time.

100 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Louis de Broglie, (France, 1892- 1987) Wave Properties of Matter (1923) Since light waves have a particle behavior (as shown by Einstein in the Photoelectric Effect), then particles could have a wave behavior. Photoelectric Effect de Broglie wavelength  h mv

101 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electron Motion Around Atom Shown as a de Broglie Wave

102 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Davisson and Germer (USA, 1927) confirmed de Broglie’s hypothesis for electrons. Electrons produced a diffraction pattern similar to x-rays.

103 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Erwin Schrodinger, 1925 Quantum (wave) Mechanical Model of the Atom Four quantum numbers are required to describe the state of the hydrogen atom.

104 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Orbital: A region in space in which there is high probability of finding an electron.

105 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Comparing Models of Atoms Chapter 3 PLAY

106 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electrons and Light By 1900, scientists knew that light could be thought of as moving waves that have given frequencies, speeds, and wavelengths. Light waves are electromagnetic waves and light is a form of electromagnetic radiation (A form of energy called radiant energy that travels at the speed of light with wave-like behavior). All waves, whether they are water waves or electromagnetic waves, can be described in terms of four characteristics-amplitude, wavelength, frequency, and speed. Section 3 Electron Configuration Chapter 3

107 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Nature of Waves What is a wave? A wave is a repeating disturbance or movement that transfers energy through matter or space

108 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Waves transfer energy not matter. The water waves below are carrying energy but are not moving. Waves can only exist as they have energy to carry.

109 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu What are the parts of a wave? The crest is the highest point on a wave. The trough is the lowest point on a wave. The rest position of the wave is called the node or nodal line.

110 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electrons and Light Characteristics of a wave. 1)The amplitude of a wave is the height of the wave measured from the origin to its crest, or peak.

111 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electrons and Light Characteristics of a wave. 2)The wavelength, λ (lambda) is the distance between successive crests of the wave. It is the distance that the wave travels as it completes one full cycle of upward and downward motion. Section 3 Electron Configuration Chapter 3

112 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electrons and Light Characteristics of a wave. 3)The frequency, v (nu) of a wave tells how fast the wave oscillates up and down. The frequency of light is measured by the number of times a light wave completes a cycle of upward and downward motion in one second. Thus, the unit for frequency is cycles per second. Because it is understood that cycles are involved, frequency is commonly expressed simply as "per second," which is written as s -1 or 1/s. A cycle per second is also called a hertz (Hz): 1 Hz = 1 s -1. Section 3 Electron Configuration Chapter 3

113 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electrons and Light 4)Light, regardless of its wavelength, moves through space at a constant speed of 3.00 x 10 8 meters per second (m/s), which is the speed of light, c Because light moves at a constant speed, there is a relationship between its wavelength and its frequency. The shorter the distance between the crests of the wave, the faster the wave oscillates up and down. That is, the shorter the wavelength, the greater the frequency. This relationship can be expressed in a simple equation. Using the symbol λ (the Greek letter lambda) for wavelength, v (the Greek letter nu) for frequency, and c for the speed of light, the relationship between wavelength and frequency is C=λv Section 3 Electron Configuration Chapter 3

114 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu C=λν λ is inversly proportional to the ν

115 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Characteristics of a Wave Chapter 3 PLAY

116 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electromagnetic Spectrum Section 3 Electron Configuration Chapter 3

117 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Electromagnetic Spectrum Chapter 3

118 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electrons and Light, continued The electromagnetic spectrum is all of the frequencies or wavelengths of electromagnetic radiation. The wavelength of light can vary from 10 5 m to less than 10 –13 m. In 1905, Albert Einstein proposed that light also has some properties of particles. His theory would explain a phenomenon known as the photoelectric effect. This effect happens when light strikes a metal and electrons are released. Section 3 Electron Configuration Chapter 3

119 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electrons and Light, continued Einstein proposed that light has the properties of both waves and particles. Light can be described as a stream of particles, the energy of which is determined by the light’s frequency. Light is an electromagnetic wave. Red light has a low frequency and a long wavelength. Violet light has a high frequency and a short wavelength. The frequency and wavelength of a wave are inversely related. Section 3 Electron Configuration Chapter 3

120 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electrons and Light, continued Light is an electromagnetic Wave, continued The frequency and wavelength of a wave are inversely related. As frequency increases, wavelength decreases. Section 3 Electron Configuration Chapter 3

121 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Wavelength and Frequency Section 3 Electron Configuration Chapter 3

122 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electrons and Light, continued Light Emission When a high-voltage current is passed through a tube of hydrogen gas at low pressure, lavender-colored light is seen. When this light passes through a prism, you can see that the light is made of only a few colors. This spectrum of a few colors on a black background that is related to electron transitions from higher energy levels to lower energy level s is called a line-emission spectrum. Experiments with other gaseous elements show that each element has a line-emission spectrum that is made of a different pattern of colors. Section 3 Electron Configuration Chapter 3

123 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electrons and Light, continued Light Emission, continued In 1913, Bohr showed that hydrogen’s line-emission spectrum could be explained by assuming that the hydrogen atom’s electron can be in any one of a number of distinct energy levels. An electron can move from a low energy level to a high energy level by absorbing energy. Electrons at a higher energy level are unstable and can move to a lower energy level by releasing energy. This energy is released as light that has a specific wavelength. Each different move from a particular energy level to a lower energy level will release light of a different wavelength. Section 3 Electron Configuration Chapter 3

124 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electrons and Light, continued Light Provides Information About Electrons An electron in a state of its lowest possible energy, is in a ground state. The ground state is the lowest energy state of a quantized system If an electron gains energy, it moves to an excited state. An excited state is a state in which an atom has more energy than it does at its ground state An electron in an excited state will release a specific quantity of energy as it quickly “falls” back to its ground state. Section 3 Electron Configuration Chapter 3

125 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electrons and Light, continued Light Provides Information About Electrons, continued An electron in a hydrogen atom can move between only certain energy states, shown as n = 1 to n = 7. In dropping from a higher energy state to a lower energy state, an electron emits a characteristic wavelength of light. Section 3 Electron Configuration Chapter 3

126 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Hydrogen’s Line-Emission Spectrum Section 3 Electron Configuration Chapter 3

127 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Absorption and Emission Spectra Chapter 3 PLAY

128 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Quantum Numbers The present-day model of the atom is also known as the quantum model. According to this model, electrons within an energy level are located in orbitals, regions of high probability for finding a particular electron. The model does not explain how the electrons move about the nucleus to create these regions. Heinsenberg Uncertainity Principle To define the region in which electrons can be found, scientists have assigned four quantum numbers that specify the properties of the electrons. A quantum number is a number that specifies the properties of electrons. Section 3 Electron Configuration Chapter 3

129 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Quantum Numbers, continued 1) The principal quantum number, symbolized by n, indicates the main energy level occupied by the electron. Values of n are positive integers, such as 1, 2, 3, 4, ∞ As n increases, the electron’s distance from the nucleus and the electron’s energy increases. Max # e- is 2n 2 Section 3 Electron Configuration Chapter 3

130 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Principal Quantum Number Chapter 3 PLAY

131 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Quantum Numbers, continued 2) The main energy levels can be divided into sublevels. These sublevels are represented by the angular momentum quantum number, l. This quantum number indicates the shape or type of orbital that corresponds to a particular sublevel. A letter code is used for this quantum number. l = 0 corresponds to an s orbital l = 1 to a p orbital l = 2 to a d orbital l = 3 to an f orbital Section 3 Electron Configuration Chapter 3

132 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu

133 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Quantum Numbers, continued 3) The magnetic quantum number, symbolized by m, is a subset of the l quantum number. It also indicates the numbers and orientations of orbitals around the nucleus. The value of m takes whole-number values, depending on the value of l. The number of orbitals includes one s orbital three p orbitals five d orbitals seven f orbitals Section 3 Electron Configuration Chapter 3

134 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Quantum Numbers, continued 4) The spin quantum number, m s indicates the orientation of an electron’s magnetic field relative to an outside magnetic field. The spin quantum number is represented by: Section 3 Electron Configuration Chapter 3 A single orbital can hold a maximum of two electrons, which must have opposite spins.

135 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Quantum Numbers and Orbitals Chapter 3 PLAY

136 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Quantum Numbers, continued Quantum Numbers of the First 30 Atomic Orbitals Section 3 Electron Configuration Chapter 3

137 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu In 1925 the German chemist Wolfgang Pauli established a rule is known as the Pauli exclusion principle. The Pauli exclusion principle states that two particles of a certain class cannot be in the exact same energy state. This means that that no two electrons in the same atom can have the same four quantum numbers. Section 3 Electron Configuration Chapter 3

138 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Pauli Exclusion Principle Chapter 3 PLAY

139 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Two electrons can have the same value of n by being in the same main energy level. These two electrons can also have the same value of l by being in orbitals that have the same shape. These two electrons may also have the same value of m by being in the same orbital. But these two electrons cannot have the same spin quantum number. If one electron has the value of 1/2, then the other electron must have the value of –1/2. Section 3 Electron Configuration Chapter 3

140 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Shapes of s, p, and d Orbitals Section 3 Electron Configuration Chapter 3

141 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Homework: Worksheet on Quantum Numbers QUIZ on Section 3 to this point next class

142 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electron Configurations The arrangement of electrons in the ground state of an atom is usually shown by writing an electron configuration or an orbital notation. Like all systems in nature, electrons in atoms tend to assume arrangements that have the lowest possible energies. An electron configuration of an atom shows the lowest-energy arrangement of the electrons for the element. Section 3 Electron Configuration Chapter 3

143 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electron configurations vs Orbital Notation

144 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Orbital Notation Chapter 3 PLAY

145 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electron Configurations, continued An Electron Occupies the Lowest Energy Level Available The aufbau principle states that electrons fill orbitals that have the lowest energy first. Aufbau is the German word for “building up.” The smaller the principal quantum number, the lower the energy. Within an energy level, the smaller the l quantum number, the lower the energy. So, the order in which the orbitals are filled matches the order of energies. 1s < 2s < 2p < 3s < 3p Section 3 Electron Configuration Chapter 3

146 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electron Configurations, continued An Electron Occupies the Lowest Energy Level Available, continued The energy of the 3d orbitals is slightly higher than the energy of the 4s orbitals. As a result, the order in which the orbitals are filled is as follows: 1s < 2s < 2p < 3s < 3p < 4s < 3d Additional irregularities occur at higher energy levels. Section 3 Electron Configuration Chapter 3

147 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electron Configurations, continued An Electron Occupies the Lowest Energy Level Available, continued This diagrams shows how the energy of the orbitals can overlap. Section 3 Electron Configuration Chapter 3

148 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Aufbau Principle Chapter 3 PLAY

149 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu See Handout for notes Aufbau Principle a) Memorize b) Periodic table c) Diagonal Rule

150 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Blocks of the Periodic Table Section 1 How Are Elements Organized? Chapter 4 4f 5f

151 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts s Orbitals Chapter 3 PLAY

152 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts p Orbitals Chapter 3 PLAY

153 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts d Orbitals Chapter 3 PLAY

154 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Electron Configuration Chapter 3 PLAY

155 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electron Configurations, continued An Electron Configuration Is a Shorthand Notation, continued Electron orbitals are filled according to Hund’s Rule. Hund’s rule states that orbitals of the same n and l quantum numbers are each occupied by one electron before any pairing occurs. Orbital diagram for sulfur Section 3 Electron Configuration Chapter 3

156 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electron Configurations, continued An Electron Configuration Is a Shorthand Notation Based on the quantum model of the atom, the arrangement of the electrons around the nucleus can be shown by the nucleus’s electron configuration. Example: sulfur has sixteen electrons. Its electron configuration is written as 1s 2 2s 2 2p 6 3s 2 3p 4. Two electrons are in the 1s orbital, two electrons are in the 2s orbital, six electrons are in the 2p orbitals, two electrons are in the 3s orbital, and four electrons are in the 3p orbitals. Section 3 Electron Configuration Chapter 3

157 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Examples of both Electron Configuration and Orbital Notation 2 worksheets for homework. QUIZ to follow.

158 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electron Configurations, continued An Electron Configuration As a Shorthand Notation, continued Each element’s configuration builds on the previous elements’ configurations. To save space, one can write this configuration by using a configuration of a noble gas. neon, argon, krypton, and xenon The neon atom’s configuration is 1s 2 2s 2 2p 6, so the electron configuration of sulfur is [Ne] 3s 2 3p 4 Section 3 Electron Configuration Chapter 3

159 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Noble Gas Notation Chapter 3 PLAY

160 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Sample Problem C Writing Electron Configurations Write the electron configuration for an atom whose atomic number is 20. Chapter 3 Section 3 Electron Configuration

161 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Sample Problem C Solution atomic number = number of protons = number of electrons = 20 According to the aufbau principle, the order of orbital filling is 1s,2s, 2p, 3s, 3p, 4s, 3d, 4p, and so on. The electron configuration for an atom of this element is written as follows: 1s22s22p63s23p64s21s22s22p63s23p64s2 This electron configuration can be abbreviated as follows: [Ar]4s 2 Chapter 3 Section 3 Electron Configuration

162 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The electrons in the outer shell are called valence electrons. Valence electrons are found in the outermost shell of an atom and that determines the atom’s chemical properties. Elements with the same number of valence electrons tend to react in similar ways. Because s and p electrons fill sequentially, the number of valence electrons in s- and p-block elements are predictable. Chapter 3

163 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Valence Electrons valence electrons are the electrons in the OUTERMOST energy level… that’s why we did all those electron configurations!valence electrons are the electrons in the OUTERMOST energy level… that’s why we did all those electron configurations! B is 1s 2 2s 2 2p 1 ; so the outer energy level is 2, and there are 2+1 = 3 electrons in level 2. These are the valence electrons!B is 1s 2 2s 2 2p 1 ; so the outer energy level is 2, and there are 2+1 = 3 electrons in level 2. These are the valence electrons! Br is [Ar] 4s 2 3d 10 4p 5 How many valence electrons are present?Br is [Ar] 4s 2 3d 10 4p 5 How many valence electrons are present?

164 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Valence Electrons Valence Electrons Number of valence electrons of a main (A) group atom = Group number

165 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electron Dot Structures Symbols of atoms with dots to represent the valence-shell electrons 1 2 13 14 15 16 17 18 H  He:            Li  Be   B   C   N   O  : F  : Ne :                    Na  Mg   Al   Si   P   S  : Cl  : Ar :        

166 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Worksheet for Homework Quiz to Follow

167 Section 4 Counting Atoms Bellringer A penny has 2.97  10 22 copper atoms. On a sheet of paper, write out this number in regular notation with all the zeros. What does this tell you about the size of an atom? Chapter 3

168 Objectives Compare the mass quantities and units for atomic mass with those for molar mass. Define mole, and explain why this unit is used to count atoms. Calculate either mass with molar mass or number with Avogadro’s number given an amount in moles. Section 4 Counting Atoms Chapter 3

169 List some common Counting Units

170 A counting unit Similar to a dozen, except instead of 12, it’s 602 billion trillion 602,200,000,000,000,000,000,000 6.022 X 10 23 (in scientific notation) This number is named in honor of Amedeo Avogadro(1776 – 1856)

171 quantity We will first consider how people normally keep track of quantity in everyday life. There are generally three ways to do this: by numberCounting  by number of units. Example: oranges priced by number. lump sum. If a single unit is too small, we devise a lump sum. Example: eggs are priced by the dozen, which is a lump sum of 12 units. by weight or mass.Weighing  by weight or mass. Example: meat is priced by the pound. by volume.Measuring  by volume. This is easier to use with liquids or gases. Example: gasoline is priced by the gallon. How we determine quantity: Counting, Weighing or Volume Measurement

172 Is it surprising to you that we employ similar ways in chemistry to keep track of atoms and molecules as described above? But, indeed we do. The next two slides compare two parallel ways of counting by number of units: As we count small items by the “dozen” in everyday life, we count atoms and molecules by the “mole” in chemistry.

173 How many eggs are in 15 dozen eggs? How many dozens of donuts are in 26 donuts?

174 How many atoms are in 57 dozen of Al atoms? How many dozen of atoms are in 1.8 * 10 5 Fe?

175 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu How many atoms are in 57 mole of Al atoms? How many moles of atoms are in 1.8 * 10 5 Fe?

176 Previous slides showed how counting eggs in dozens is similar to counting atoms by the mole. We use similar math equations for both mole number conversions and dozen number conversions. Since everyday items contain astronomical numbers of atoms and molecules, it is easier to count them by a huge lump sum: 1 mole = 6.022 x 10 23

177 But why do we use Avogadro’s number, 6.022 x 10 23, for one mole? Did he invent the number? No, neither he nor anyone else did. The number is defined by how the mass units, amu and gram, relate to each other: amu is the mass of one atom units are atomic mass unit 1 amu = 1.66058 x 10 -24 grams

178 Experimental data: 1 amu = 1.66058 x 10 -24 grams leads to this equality: 6.022 x 10 23 amu = 1 gram because: 1 / (1.66058 x 10 -24 ) = 6.022 x 10 23

179 Mole Trivia The mole is a REALLY BIG number!!!! Just how big is it?

180 Just How Big is a Mole? If you had Avogadro's number of soft drink cans to cover the surface of the earth to a depth of over 200 miles. If you had Avogadro's number of unpopped popcorn kernels, and spread them across the United States of America, the country would be covered in popcorn to a depth of over 9 miles. If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years to count the atoms in one mole.

181 Mole Trivia The mole is a REALLY BIG number!!!! Just how big is it?

182 Mole Trivia If there were a mole of rice grains, all the land area in the whole world would be covered with rice to a depth of about 75 meters. One mole of rice grains is more grains than all the grain that has been grown since the beginning of time. (1) One mole of rice would occupy a cube about 120 miles on an edge! (1)

183 Mole Trivia The mole is a REALLY BIG number!!!! Just how big is it?

184 Mole Trivia A mole of marshmallows would cover the United States to a depth of 600 miles (3) In order to put a mole of rain drops in a 30 meter (about 100 feet) diameter tank, the sides of the tank would have to be 280 times the distance from the Earth to the Sun. (4) A mole of hockey pucks would be equal to the mass of the Moon.

185 Mole Trivia The mole is a REALLY BIG number!!!! Just how big is it?

186 Mole Trivia Assuming that each human being has 60 trillion body cells (6.0 x 10 13 ) and the Earth's population is 6 billion (6 x 10 9 ), the total number of living human body cells on the Earth at the present time is 3.6 x 10 23 or a little over half of a mole.

187 Mole Trivia The mole is a REALLY BIG number!!!! Just how big is it?

188 Mole Trivia If one mole of pennies were divided up among the Earth's population, each person would receive 1 x 10 14 pennies. Personal spending at the rate of one million dollars a day would use up each persons wealth in about three thousand years. Life would not be comfortable because the surface of the Earth would be covered in copper coins to a depth of at least 400 meters.

189 Mole Trivia The mole is a REALLY BIG number!!!! Just how big is it?

190 Mole Trivia If you had a mole of pennies and wanted to buy kite string at the rate of a million dollars per inch, you would get your money's worth. After stretching your string around the Earth one million times, and to the Moon and back twenty- five times, you would have enough string left over to sell back at a dollar an inch (a decided loss) to gain enough money to buy every man, woman and child in the US a $50,000 automobile and enough gasoline to run it at 55 mph for a year. After those purchases, you would still have enough money left over to give every man, woman, and child in the whole world about $5000.

191 Mole Trivia Basis for calculations: –Earth's circumference = 25,000 miles –Distance to moon = 240,000 miles –Cost of gasoline = $2.50 per gallon –Gasoline mileage = 20 miles per gallon –U.S. population =220,000,000 –World population = 6,000,000,000

192 Given the chemical composition of an everyday item, we can easily determine the number of atoms or molecules present in it by applying the conversions we have practiced in the previous slides

193 Avogadro’s Number The standard laboratory unit of mass is the gram. We would like to choose a number of atoms which would have a mass in grams equivalent to the mass of one atom in atomic mass units. The same number would fit all elements since equal numbers of different atoms always have the same mass ratio.

194 There is one problem in using the molecular and formula masses of substances. These masses are in atomic mass units, which is only 1.66 x 10 -24 g. The mass of a single molecule is so small that it is impossible to measure it in the laboratory. For everyday use in chemistry, a larger unit, such as a gram, is needed.

195 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu http://www.youtube.com/watch?v=TqDqLmwWx3A

196 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Mass, continued Masses of Atoms Are Expressed in Atomic Mass Units A special mass unit is used to express atomic mass. This unit has two names—the atomic mass unit (amu) and the Dalton (Da). Section 4 Counting Atoms Chapter 3

197 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Introduction to the Mole Most samples of elements have great numbers of atoms. A mole is defined as the number of atoms in exactly 12 grams of carbon-12.The mole is the SI unit for the amount of a substance. The molar mass of an element is the mass in grams of one mole of the element. Molar mass has the unit grams per mol (g/mol). The mass in grams of 1 mol of an element is numerically equal to the element’s atomic mass from the periodic table in atomic mass units. Section 4 Counting Atoms Chapter 3

198 Other Names Related to Molar Mass Molecular Mass/Molecular Weight: If you have a single molecule, mass is measured in amu’s instead of grams. But, the molecular mass/weight is the same numerical value as 1 mole of molecules. Only the units are different. (This is the beauty of Avogadro’s Number!) Formula Mass/Formula Weight: Same goes for compounds. But again, the numerical value is the same. Only the units are different. THE POINT: You may hear all of these terms which mean the SAME NUMBER… just different units

199 Find the molar mass (usually we round to the hundreths place) Learning Check! A.1 mole of Br atoms B.1 mole of Sn atoms =79.90 g/mole = 118.69 g/mole

200 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Molar Mass Chapter 3

201 molar mass Grams Moles Calculations with Molar Mass

202 What is in a Mole? It is important to note that; one mole of atoms = 6.022 x 10 23 atoms one mole of atoms= molar mass in grams 1 mole of Cu = 6.022 x 10 23 atoms of Cu 1 mole of Cu = 63.55 g of Cu

203 mol= ___________atoms atoms=__________mol g=_____________mol mol=____________g g=____________atoms atoms=__________g

204 These problems can be solved in TWO ways: 1) Factor Label Method (conversion factors)(proportions) We know that: 1 mole of a element = 6.022 x 10 23 atoms of that element = molar mass (atomic weight) in grams Given (units given) x Conversion ( units of unknown) = desired answer 1factor (units of given)

205 6.022 x 10 23 particles 1 mole or 1 mole 6.02 x 10 23 particles Note that a particle could be an atom OR a molecule! Avogadro’s Number as Conversion Factor

206 Using Formulas Molar Mass = mass ÷ moles Mass (grams of the subs.) = (moles) (Molar Mass) Moles = Mass (grams of the subs.) ÷ Molar Mass Number of Particles = (Moles) (Avogadro’s #) Ex) What is the mass in grams of 0.586 mol Zn atoms?

207 Aluminum is often used for the structure of light-weight bicycle frames. How many grams of Al are in 3.00 moles of Al? 3.00 moles Al ? g Al Converting Moles and Grams

208 1. Molar mass of Al1 mole Al = 27.0 g Al 2. Conversion factors for Al 27.0g Al or 1 mol Al 1 mol Al 27.0 g Al 3. Setup3.00 moles Al x 27.0 g Al 1 mole Al Answer = 81.0 g Al

209 Atoms/Molecules and Grams Since 6.02 X 10 23 particles = 1 mole AND 1 mole = molar mass (grams) You can convert atoms/molecules to moles and then moles to grams! (Two step process) You can’t go directly from atoms to grams!!!! You MUST go thru MOLES. That’s like asking 2 dozen cookies weigh how many ounces if 1 cookie weighs 4 oz? You have to convert to dozen first!

210 molar mass Avogadro’s number Grams Moles particles Everything must go through Moles!!! Calculations

211 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atoms/Molecules and Grams How many atoms of Cu are present in 35.4 g of Cu? 35.4 g Cu 1 mol Cu 6.02 X 10 23 atoms Cu 63.5 g Cu 1 mol Cu = 3.4 X 10 23 atoms Cu

212 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Learning Check! How many atoms of K are present in 78.4 g of K?

213 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Learning Check! How many atoms of O are present in 78.1 g of oxygen? 78.1 g O 2 1 mol O 2 6.02 X 10 23 molecules O 2 2 atoms O 32.0 g O 2 1 mol O 2 1 molecule O 2

214 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 4 Counting Atoms Converting from Amount in Moles to Mass Sample Problem D Determine the mass in grams of 3.50 mol of copper. Chapter 3

215 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Sample Problem D Solution First, make a set-up that shows what is given and what is desired. 3.50 mol Cu  ? = ? g Cu Use a conversion factor that has g Cu in the numerator and mol Cu in the denominator. The correct conversion factor is the molar mass of Cu, 63.55 g/mol. Chapter 3 Section 4 Counting Atoms

216 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Converting from Amount in Moles to Number of Atoms Sample Problem E Determine the number of atoms in 0.30 mol of fluorine atoms. Chapter 3 Section 4 Counting Atoms

217 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 4 Counting Atoms Sample Problem E Answer To determine the number of atoms, select the conversion factor that will take you from the amount in moles to the number of atoms. amount (mol)  6.022  10 23 atoms/mol = number of atoms Chapter 3

218 Ex) How many moles are in 2.83 * x 10 25 atoms Cr? Ex) How many moles are in 6.195 g of K? Ex) How many grams are in 9.76 x 10 24 atoms of Ba?

219 Determining Moles of Atoms Aluminum (Al) is a metal with a high strength-to-mass ratio and a high resistance to corrosion: thus it is often used for structural purposes. 1.Compute the number of moles in a 10.0 gram sample of Aluminum 2.Compute the number of atoms in the same sample.

220 Answers 1.0.371 mol Al atoms 2.2.23 x 10 23 atoms

221 Calculating Numbers of Atoms A silicon chip used in an integrated circuit of a microcomputer has a mass of 5.68 mg. How many silicon (Si) atoms are present in the chip?

222 Answer 1.22 x 10 20 atoms

223 Calculating Number of Moles and Mass Cobalt (Co) is a metal that is added to steel to improve its resistance to corrosion. Calculate both the number of moles and the number of grams in a sample of cobalt containing 5.00 x 10 20 atoms of cobalt.

224 Answers 8.30 x 10 -4 mol Co 4.89 x 10 -2 g Co

225 STOP ASSIGN WORKSHEET FOR HOMEWORK QUIZ NEXT CLASS CHAPTER 3 TEST UPCOMING


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