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Chapter 4 Atomic Structure. By the end of the chapter you WILL be able to… Describe Democritus’s ideas about atoms Describe Democritus’s ideas about atoms.

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Presentation on theme: "Chapter 4 Atomic Structure. By the end of the chapter you WILL be able to… Describe Democritus’s ideas about atoms Describe Democritus’s ideas about atoms."— Presentation transcript:

1 Chapter 4 Atomic Structure

2 By the end of the chapter you WILL be able to… Describe Democritus’s ideas about atoms Describe Democritus’s ideas about atoms Explain Daltons atomic theory Explain Daltons atomic theory ID the special instruments necessary to observe individual atoms ID the special instruments necessary to observe individual atoms ID 3 types of subatomic particles ID 3 types of subatomic particles Describe the structure of atoms according to the Rutherford atomic model Describe the structure of atoms according to the Rutherford atomic model Explain what makes elements and isotopes different from each other Explain what makes elements and isotopes different from each other Calculate the number of neutrons in an atom Calculate the number of neutrons in an atom Calculate atomic mass of an element Calculate atomic mass of an element

3 Quantum Model of the Atom the-universe-stephen-hawking-atoms.html the-universe-stephen-hawking-atoms.html the-universe-stephen-hawking-atoms.html the-universe-stephen-hawking-atoms.html Currently the most accepted model Currently the most accepted model “shells” represent areas of probability of finding an electron “shells” represent areas of probability of finding an electron Here are the major Here are the major contributors… contributors…

4 Erwin Schrødinger educated in Vienna; serves in Austrian Army in WWI educated in Vienna; serves in Austrian Army in WWI 1926 publishes “wave equation” model of electrons 1926 publishes “wave equation” model of electrons Goes to Germany in 1927 but leaves in 1933 with rise of Nazis; ends up in Austria in 1937; recants opposition to Nazis but is harassed and escapes in 1938 Goes to Germany in 1927 but leaves in 1933 with rise of Nazis; ends up in Austria in 1937; recants opposition to Nazis but is harassed and escapes in Nobel Prize in Physics with Dirac 1933 Nobel Prize in Physics with Dirac 1940 establishes Institute for Advanced Studies in Dublin 1940 establishes Institute for Advanced Studies in Dublin

5 Werner Heisenberg PhD in Munich 1923 PhD in Munich 1924-’25 works with Bohr in Copenhagen 1924-’25 works with Bohr in Copenhagen establishes “quantum mechanics” when only 23 years old in includes Uncertainty Principle establishes “quantum mechanics” when only 23 years old in includes Uncertainty Principle 1932 Nobel Prize in Physics 1932 Nobel Prize in Physics 1941 director of Kaiser Wilhelm Institute in Berlin - captured by US troops at end of WWII & sent to England; returns to Germany after the war 1941 director of Kaiser Wilhelm Institute in Berlin - captured by US troops at end of WWII & sent to England; returns to Germany after the war

6 Prince Louis-Victor deBroglie educated and worked in France - BA in 1913 & graduate work after serving for France in WWI educated and worked in France - BA in 1913 & graduate work after serving for France in WWI his 1924 doctoral thesis introduced “wave mechanics” - the idea that the electron could be treated as a wave his 1924 doctoral thesis introduced “wave mechanics” - the idea that the electron could be treated as a wave 1929 Nobel Prize in Physics 1929 Nobel Prize in Physics

7 computer- generated images of “electron cloud” shapes generated by Schrødinger’s wave equation wave equationmeta-synthesis (chem education co.)

8 Lets go back in time… Lets go back in time… …and look at other models

9 Bohr’s Model Characterized by its concentric circles Bohr’s model has probably been ingrained into your heads Characterized by its concentric circles Bohr’s model has probably been ingrained into your heads However Bohr was not the first to hypothesize this model However Bohr was not the first to hypothesize this model

10 The Rutherford Atomic Model Based on his experimental evidence: Based on his experimental evidence: The atom is mostly empty space The atom is mostly empty space All the positive charge, and almost all the mass is concentrated in a small area in the center. He called this a “nucleus” All the positive charge, and almost all the mass is concentrated in a small area in the center. He called this a “nucleus” The nucleus is composed of protons and neutrons The nucleus is composed of protons and neutrons The electrons distributed around the nucleus, and occupy most of the volume The electrons distributed around the nucleus, and occupy most of the volume His model was called a “nuclear model” His model was called a “nuclear model”

11 Ernest Rutherford’s Gold Foil Experiment  Alpha particles are helium nuclei - The alpha particles were fired at a thin sheet of gold foil  Particle that hit on the detecting screen (film) are recorded

12 Rutherford’s problem: In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target? Target #1 Target #2

13 The Answers: Target #1 Target #2

14 Rutherford’s Findings a) The nucleus is small b) The nucleus is dense c) The nucleus is positively charged  Most of the particles passed right through  A few particles were deflected  VERY FEW were greatly deflected “Like howitzer shells bouncing off of tissue paper!” Conclusions:

15 Thomson’s Atomic Model Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model. J. J. Thomson

16 John Dalton ( ) Published in 1808, Dalton’s work became the basis for modern atomic theory. Published in 1808, Dalton’s work became the basis for modern atomic theory. Represented the atom as a simple sphere with no internal structure. Sketch it! Represented the atom as a simple sphere with no internal structure. Sketch it! Showed that substances were combinations of relatively few elements Showed that substances were combinations of relatively few elements

17 Dalton’s Atomic Theory Includes four parts Includes four parts 1. All elements are composed of atoms 2. Atoms of the same element are identical 3. Atoms of different elements can physically mix, or can chemically combine to form compounds 4. Chemical reactions occur when atoms are separated, joined, or combined. (atoms of one element cannot change into another element as a result of a chemical reaction) See diagram on page 102

18 Structure of the Nuclear Atom One change to Dalton’s atomic theory is that atoms are divisible into subatomic particles: One change to Dalton’s atomic theory is that atoms are divisible into subatomic particles: Electrons, protons, and neutrons are examples of these fundamental particles Electrons, protons, and neutrons are examples of these fundamental particles There are many other types of particles, but we will study these three There are many other types of particles, but we will study these three

19 Democritus of Abdera 460 B.C.E B.C.E. Believed atoms were indivisible and indestructible Believed atoms were indivisible and indestructible Believed matter was composed of atoms, the smallest part of an element which retains its identity during a chemical reaction. Believed matter was composed of atoms, the smallest part of an element which retains its identity during a chemical reaction. Atom comes from the Greek work atomos, meaning indivisible. Atom comes from the Greek work atomos, meaning indivisible. Why is the word “atom” a misnomer? Why is the word “atom” a misnomer?

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21 Foundations of Atomic Theory Atoms and the Law of Conservation of Mass… (state it) Atoms and the Law of Conservation of Mass… (state it) Atoms have mass, cannot be broken down, and you CAN put them together Atoms have mass, cannot be broken down, and you CAN put them together Therefore… A + B  C and C  A+B Therefore… A + B  C and C  A+B (synthesis) (decomposition) (synthesis) (decomposition) What can we say about the masses of the reactants and products? What can we say about the masses of the reactants and products?

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23 Sizing up the Atom Radii of most atoms fall within the range of 5x to 2x m Radii of most atoms fall within the range of 5x to 2x m The unit, Angstrom (Å), can be used when dealing with atomic radii. (1x m) The unit, Angstrom (Å), can be used when dealing with atomic radii. (1x m) Nanometers are also commonly used (1x10 -9 m) Nanometers are also commonly used (1x10 -9 m) Using the factor label method convert the above measurements to angstroms. Using the factor label method convert the above measurements to angstroms. You should have gotten… You should have gotten….5 – 2 Å How many nanometers?.5 – 2 Å How many nanometers?

24 Despite their small size atoms are observable with instruments such as the scanning tunneling microscope Despite their small size atoms are observable with instruments such as the scanning tunneling microscope First done in 1981 First done in 1981 When observed they look like this When observed they look like this

25 Problem! A sample of copper with a mass of 63.5g contains 6.02x10 23 atoms. What is the mass of a single atom of Cu? A sample of copper with a mass of 63.5g contains 6.02x10 23 atoms. What is the mass of a single atom of Cu? Answer… Answer… 1.05x g 1.05x g THINK ABOUT THIS!!!!!!!!!!!!!!!! THINK ABOUT THIS!!!!!!!!!!!!!!!! -If you lined up 100,000,000 Cu atoms side by side they would only measure 1cm long -If you lined up 100,000,000 Cu atoms side by side they would only measure 1cm long

26 Other Major Contributors and Contributions

27 Discovery of the Electron In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle: the electron See pages 104 and 105

28 Some Modern Cathode Ray Tubes  Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

29 Mass of the Electron 1916 – Robert Millikan determines the mass of the electron: 1/1840 the mass of a hydrogen atom; has one unit of negative charge The oil drop apparatus Mass of the electron is 9.11 x g

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31 Conclusions from the Study of the Electron: a)Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons. b)Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electrons c)Electrons have so little mass that atoms must contain other particles that account for most of the mass

32 Conclusions from the Study of the Electron:  Eugen Goldstein in 1886 observed what is now called the “proton” - particles with a positive charge, and a relative mass of 1 (or 1840 times that of an electron)  1932 – James Chadwick confirmed the existence of the “neutron” – a particle with no charge, but a mass nearly equal to a proton

33 Subatomic Particles ParticleCharge Mass (g) Location Electron (e - ) (e - ) 9.11 x x Electron cloud Proton (p + ) x x Nucleus Neutron (n o ) (n o ) x x Nucleus

34 Atomic Number Atoms are composed of protons, neutrons, and electrons Atoms are composed of protons, neutrons, and electrons How then are atoms of one element different from another element? How then are atoms of one element different from another element? Elements are different because they contain different numbers of PROTONS Elements are different because they contain different numbers of PROTONS The “atomic number” of an element is the number of protons in the nucleus The “atomic number” of an element is the number of protons in the nucleus # protons in an atom = # electrons # protons in an atom = # electrons

35 Atomic Number Atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element. Element # of protons Atomic # (Z) Carbon66 Phosphorus1515 Gold7979

36 Isotopes Dalton (thinking back to his theory) was wrong about all elements of the same type being identical Dalton (thinking back to his theory) was wrong about all elements of the same type being identical Atoms of the same element can have different numbers of neutrons. Atoms of the same element can have different numbers of neutrons. Thus, different mass numbers. Thus, different mass numbers. These are called isotopes. These are called isotopes.

37 Isotopes Elements occur in nature as mixtures of isotopes. Isotopes are atoms of the same element that differ in the number of neutrons.

38 Naming Isotopes We can also put the mass number after the name of the element: nuclides… We can also put the mass number after the name of the element: nuclides… carbon-12 carbon-12 carbon-14 carbon-14 uranium-235 uranium-235

39 Mass Number Mass number is the number of protons and neutrons in the nucleus of an isotope: Mass # = p + + n 0 Nuclide p+p+p+p+ n0n0n0n0 e-e-e-e- Mass # Oxygen Arsenic Phosphorus

40 Nuclear Symbols Contain the symbol of the element, the mass number and the atomic number. Contain the symbol of the element, the mass number and the atomic number. X Mass number Atomic number Subscript → Superscript →

41 Symbols n Find each of these: a) number of protons b) number of neutrons c) number of electrons d) Atomic number e) Mass Number Br 80 35

42 Symbols n If an element has an atomic number of 34 and a mass number of 78, what is the: a) number of protons b) number of neutrons c) number of electrons d) complete symbol

43 Symbols n If an element has 91 protons and 140 neutrons what is the a) Atomic number b) Mass number c) number of electrons d) complete symbol

44 Symbols n If an element has 78 electrons and 117 neutrons what is the a) Atomic number b) Mass number c) number of protons d) complete symbol

45 Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons. IsotopeProtonsElectronsNeutronsNucleus Hydrogen–1 (protium) (protium)110 Hydrogen-2(deuterium)111 Hydrogen-3(tritium)112

46 Atomic Mass  How heavy is an atom of oxygen?  It depends, because there are different kinds of oxygen atoms.  We are more concerned with the average atomic mass.  This is based on the abundance (percentage) of each variety of that element in nature.  We don’t use grams for this mass because the numbers would be too small.

47 Measuring Atomic Mass Instead of grams, the unit we use is the Atomic Mass Unit (amu) Instead of grams, the unit we use is the Atomic Mass Unit (amu) It is defined as one-twelfth the mass of a carbon-12 atom. It is defined as one-twelfth the mass of a carbon-12 atom. Carbon-12 chosen because of its isotope purity. Carbon-12 chosen because of its isotope purity. Each isotope has its own atomic mass, thus we determine the average from percent abundance. Each isotope has its own atomic mass, thus we determine the average from percent abundance.

48 To calculate the average: Multiply the atomic mass of each isotope by it’s abundance (expressed as a decimal), then add the results. Multiply the atomic mass of each isotope by it’s abundance (expressed as a decimal), then add the results. If not told otherwise, the mass of the isotope is expressed in atomic mass units (amu) If not told otherwise, the mass of the isotope is expressed in atomic mass units (amu)

49 Atomic Masses IsotopeSymbol Composition of the nucleus % in nature Carbon C 6 protons 6 neutrons 98.89% Carbon C 6 protons 7 neutrons 1.11% Carbon C 6 protons 8 neutrons <0.01% Atomic mass is the average of all the naturally occurring isotopes of that element. Carbon =

50 Law of Multiple Proportions Law of Multiple Proportions If two elements form more than one compound between them, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers. (not decimals) For example, H 2 O and H 2 O 2. If two elements form more than one compound between them, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers. (not decimals) For example, H 2 O and H 2 O 2. Law of Constant Proportions Law of Constant Proportions Every pure substance always contains the same elements combined in the same proportions by weight Every pure substance always contains the same elements combined in the same proportions by weight

51 Law of Multiple Proportions Law of Multiple Proportions If two elements form more than one compound between them, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers. (not decimals) For example, H 2 O and H 2 O 2. If two elements form more than one compound between them, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers. (not decimals) For example, H 2 O and H 2 O 2. Law of Constant Proportions Law of Constant Proportions Every pure substance always contains the same elements combined in the same proportions by weight Every pure substance always contains the same elements combined in the same proportions by weight

52 Question Solution Answer Knowns and Unknown

53 The Periodic Table: A Preview  A “periodic table” is an arrangement of elements in which the elements are separated into groups based on a set of repeating properties  The periodic table allows you to easily compare the properties of one element to another

54 The Periodic Table: A Preview  Each horizontal row (there are 7 of them) is called a period  Each vertical column is called a group, or family  Elements in a group have similar chemical and physical properties  Identified with a number and either an “A” or “B”  More presented in Chapter 6


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