Presentation on theme: "17 Chapter 17: Properties of Atoms and the Periodic Table Unit 4: The Nature of Matter Table of Contents 17.3: The Periodic TableThe Periodic Table 17.1:"— Presentation transcript:
17 Chapter 17: Properties of Atoms and the Periodic Table Unit 4: The Nature of Matter Table of Contents 17.3: The Periodic TableThe Periodic Table 17.1: Structure of the AtomStructure of the Atom 17.2: Masses of AtomsMasses of Atoms
Scientists have developed their own shorthand for dealing with long, complicated names. Chemical symbols consist of one capital letter or a capital letter plus one or two smaller letters. Scientific Shorthand 17.1 Structure of the Atom
For some elements, the symbol is the first letter of the element's name. For other elements, the symbol is the first letter of the name plus another letter from its name. Scientific Shorthand 17.1 Structure of the Atom Because scientists worldwide use this system, everyone understands what the symbols mean.
An element is matter that is composed of one type of atom, which is the smallest piece of matter that still retains the property of the element. Atoms are composed of particles called protons, neutrons, and electrons. Atomic Components 17.1 Structure of the Atom Click image to view movie
Protons and neutrons are found in a small positively charged center of the atom called the nucleus that is surrounded by a cloud containing electrons. Protons are particles with an electrical charge of 1+. Atomic Components 17.1 Structure of the Atom
Electrons are particles with an electrical charge of 1–. Atomic Components 17.1 Structure of the Atom Neutrons are neutral particles that do not have an electrical charge.
Protons and neutrons are made up of smaller particles called quarks. Quarks—Even Smaller Particles 17.1 Structure of the Atom So far, scientists have confirmed the existence of six uniquely different quarks.
Scientists theorize that an arrangement of three quarks held together with the strong nuclear force produces a proton. 17.1 Structure of the Atom Another arrangement of three quarks produces a neutron Quarks—Even Smaller Particles
To study quarks, scientists accelerate charge particles to tremendous speeds and then force them to collide with—or smash into— protons. This collision causes the proton to break apart. Finding Quarks 17.1 Structure of the Atom The particles that result from the collision can be detected by various collection devises.
Scientists and engineers use models to represent things that are difficult to visualize—or picture in your mind. Models—Tools for Scientists 17.1 Structure of the Atom Scaled-down models allow you to see either something too large to see all at once, or something that has not been built yet. Scaled-up models are often used to visualize things that are too small to see.
Studying Atoms Different Models of the atom – Greek Model –Dalton’s Atomic Theory –Thomson’s Model –Rutherford’s Atomic Theory –Bohr’s Model of the Atom –Electron Cloud Model
To study the atom, scientists have developed scaled-up models that they can use to visualize how the atom is constructed. Models—Tools for Scientists 17.1 Structure of the Atom For the model to be useful, it must support all of the information that is known about matter and the behavior of atoms.
Aristotle Aristotle thought that all substances were built up from only 4 elements –Earth –Air –Fire –Water These elements were a combination of 4 qualities hot, cold, dry, and wet
The Hellenic Market FireWaterEarth Air ~ ~
Aristotle did not think there was a limit to the number of times matter could be divided.Aristotle did not think there was a limit to the number of times matter could be divided. »For centuries people believed this model.
The Greek philosopher Democritus (460 B.C. – 370 B.C.) was among the first to suggest the existence of atoms (from the Greek word “atomos”) ATOM –He believed that atoms were indivisible and indestructible –His ideas did agree with later scientific theory, but did not explain chemical behavior, and was not based on the scientific method– but just philosophy Defining the Atom
Greek Model Greek philosopher Idea of ‘democracy’ Idea of ‘atomos’ –Atomos = ‘indivisible’ –‘Atom’ is derived No experiments to support idea Continuous vs. discontinuous theory of matter Democritus’s model of atom No protons, electrons, or neutrons Solid and INDESTRUCTABLE Democritus “To understand the very large, we must understand the very small.”
Who Was Right? Greek society was slave based Beneath famous to work with hands did not experiment Greeks settled disagreements by argument Aristotle was more famous He won! His ideas carried through middle ages. Alchemists change lead to gold California WEB
John Dalton (1766- 1844) was known as the “Father of the modern atom modern atom.” He was the first to actually test, previously the Greeks would just theorize. In his work he developed Dalton's Atomic Theory.
In the 1800s, John Dalton, an English scientist, was able to offer proof that atoms exist. The Changing Atomic Model 17.1 Structure of the Atom Because Dalton’s atomic theory was proven through many experiments His THEORY became widely accepted.
4) Atoms of different elements combine in simple whole-number ratios to form chemical compounds 5) In a particular compound, atoms of different elements always combine in the same way 6) All atoms of the same element have the same mass, atoms of diff. elements have diff. masses 1)All elements are composed of tiny indivisible particles called atoms 2)Atoms of the same element are identical. 3)Atoms Can’t be Created nor Destroyed! John Dalton (1766 – 1844) Dalton’s Atomic Theory (experiment based)
Dalton’s Model The Elements are pictured as solid spheres: Each type of atom is represented by a tiny, solid sphere with a different mass.
Dalton’s Elements John Dalton 1808
JJ. Thomson J.J. used the idea behind charges: -- Like charges repel -- Unlike charges attract With this idea in mind, J.J. used electric current to study the atom. Remember my ex: with the Magnets
Sir William Crookes (1832 - 1919) was the British scientist who invented the cathode ray tube. His work paved the way to the discovery of the electron. Crooke’s Tube + - vacuum tube metal disks voltage source magnet William Crookes
Discovery of the Electron Looking at what JJ saw, what do you think he determined was the charge on the particles in the beam?
Thomson’s Experiment + - voltage source OFF ON + - By adding an electric field… he found that the moving pieces were negative.
In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle: the electron The Electron was named by G. Johnstone Stoney ! ** Thomsons experiments were the 1 st proof that atoms are made of smaller particles.
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 10 -28 g
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
Magnetic Properties Show ex: of Plastic rubbed in hair and held to Water Source!
Cathode ray tubes pass electricity through a gas that is contained at a very low pressure. Some Modern Cathode Ray Tubes
J.J. Thomson J.J. reasoned that if the atom had negative little particles inside it, but was considered to be NEUTRAL, then there must also be some positive particles too.
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
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
Rutherford’s Atomic Theory
Ernest Rutherford (1871-1937) Learned physics in J.J. Thomson’ lab. Noticed that ‘alpha’ particles were sometime deflected by something in the air. 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 Ernest Rutherford’s Gold Foil Experiment - 1911
Rutherford ‘Scattering’ 1.In 1909 Rutherford undertook a series of experiments 2.He fired (alpha) particles at a very thin sample of gold foil 3.According to the Thomson model the particles should only be slightly deflected 4. Rutherford discovered that they were deflected through large angles and could even be reflected straight back to the source particle source Lead collimator Gold foil
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
The Answers: Target #1 Target #2
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:
152 mm howitzer-gun M1937
The Rutherford Atomic Model Based on his experimental evidence: 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”
The nucleus is composed of protons and neutronsThe nucleus is composed of protons and neutrons –The electrons distributed around the nucleus, and occupy most of the volume –His model was called a “nuclear model” The Rutherford Atomic Model
Bohr’s Model of the Atom
Niels Bohr In the Bohr Model (1913) the neutrons and protons occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun. They are not confined to a planar orbit like the planets are.
Bohr Model After Rutherford’s discovery, Bohr proposed that electrons travel in definite orbits at constant speeds around the nucleus like planets around the sun. Planetary model
Staircase Idea To understand energy levels, picture them as steps in a staircase. Just as you can’t stand on 2 steps at one time, Electrons can’t occupy more than 1 energy level at a time. Bottom step = Lowest Energy Level Top Step = Highest Energy Level Cont…
Staircase Model An electron in an ATOM can move from one energy level to another if enough energy is provided. The size of the jump ( 1 level or 2) determines the amt. of energy gained or lost.
Humor Two atoms are walking down the street. One atom says to the other, “Hey! I think I lost an electron!” The other says, “Are you sure??” “Yes, I’m positive!” A neutron walks into a restaurant and orders a couple of drinks. As she is about to leave, she asks the waiter how much she owes. The waiter replies, “For you, No Charge!!!”
By 1926, scientists had developed the electron cloud model of the atom that is in use today. The Electron Cloud Model 17.1 Structure of the Atom An electron cloud is the area around the nucleus of an atom where its electrons are most likely found.
The electron cloud is 100,000 times larger than the diameter of the nucleus. The Electron Cloud Model 17.1 Structure of the Atom In contrast, each electron in the cloud is much smaller than a single proton. Because an electron's mass is small and the electron is moving so quickly around the nucleus, it is impossible to describe its exact location in an atom. EX: Propeller of an Airplane’s wings !
Section Check 17.1 Question 1 A. atom B. quark C. neutron D. proton Which is the smallest piece of matter that still retains the property of the element?
Answer 17.1 Section Check The answer is A. An atom is the smallest piece of matter that still retains the property of the element.
Section Check 17.1 Question 2 A. protons and electrons B. protons and neutrons C. neutrons and electrons D. quarks and electrons What particles are found in the nucleus of an atom?
Answer 17.1 Section Check The answer is B. Electrons are located in an electron cloud surrounding the nucleus of the atom.
Section Check 17.1 Question 3 What is the name of the small particles that make up protons and neutrons? Answer Protons and neutrons are made of smaller particles called quarks.
Question 4 The Greek philosopher Democritus coined what word for a tiny piece of matter that cannot be divided? a.elementc. electron b.atom d. molecule Answer: Atom
Question 5 Which of the following is NOT part of John Dalton’s atomic theory? a.All elements are composed of atoms. b.All atoms of the same element have the same mass. c.Atoms contain subatomic particles. d.A compound contains atoms of more than one element. Answer: c
Question 6 Which of the following most accurately represents John Dalton’s model of the atom? a.a tiny, solid sphere with an unpredictable mass for a given element b.a hollow sphere with a dense nucleus c.a tiny, solid sphere with predictable mass for a given element d.a sphere that is hollow throughout 6) Answer: c
Question 7 JJ Thomson’s experiments provided evidence that an atom a.is the smallest particle of matter. b.contains negatively charged particles. c.has a negative charge. d.has a positive charge. Answer: b
Question 8 Rutherford’s gold foil experiment provided evidence for which of the following statements? a.Negative and positive charges are spread evenly throughout an atom. b.Alpha particles have a positive charge. c.Gold is not as dense as previously thought. d.There is a dense, positively charged mass in the center of an atom. Answer: d
Question 9 Who provided evidence for the existence of a nucleus in an atom? a.John Daltonc.Democritus b.J.J. Thomsond.Ernest Rutherford Answer: d.
Question 10 In an atomic model that includes a nucleus, positive charge is a.concentrated in the center of an atom b.spread evenly throughout an atom. c.concentrated at multiple sites in an atom. d.located in the space outside the nucleus. Answer: a
Atomic Mass The nucleus contains most of the mass of the atom because protons and neutrons are far more massive than electrons. The mass of a proton is about the same as that of a neutron— approximately Masses of Atoms 17.2
Atomic Mass The mass of each is approximately 1,836 times greater than the mass of the electron. Masses of Atoms 17.2
Atomic Mass The unit of measurement used for atomic particles is the ______________________. The mass of a proton or a neutron is almost equal to 1 amu. The atomic mass unit is defined as one- twelfth the mass of a carbon atom containing six protons and six neutrons. Masses of Atoms 17.2 atomic mass unit (amu)
Protons Identify the Element The number of protons tells you what type of atom you have and vice versa. For example, every carbon atom has six protons. Also, all atoms with six protons are carbon atoms. The number of protons in an atom is equal to a number called the atomic number. Masses of Atoms 17.2
Mass Number The mass number of an atom is the sum of the number of protons and the number of neutrons in the nucleus of an atom. Masses of Atoms 17.2
Mass Number If you know the mass number and the atomic number of an atom, you can calculate the number of neutrons. Masses of Atoms number of neutrons = mass number – atomic number 17.2
Isotopes Not all the atoms of an element have the same number of neutrons. Atoms of the same element that have different numbers of neutrons are called isotopes. Remember – Protons Never Change Masses of Atoms 17.2
Identifying Isotopes Models of two isotopes of boron are shown. Because the numbers of neutrons in the isotopes are different, the mass numbers are also different. You use the name of the element followed by the mass number of the isotope to identify each isotope: boron- 10 and boron-11. Masses of Atoms 17.2
M&M Lab Tomorrow
Identifying Isotopes The average atomic mass of an element is the weighted-average mass of the mixture of its isotopes. For example, four out of five atoms of boron are boron-11, and one out of five is boron-10. Masses of Atoms To find the weighted-average or the average atomic mass of boron, you would solve the following equation: 17.2
Plug the following in on a calculator Order: 1. 4 / 5 X 11 = ? 2. 1 / 5 X 10 = ? 3. Add the 2 numbers = ?
Section Check 17.2 Question 1 How is the atomic number of an element determined? Answer The atomic number of an element is equal to the number of protons in an atom of that element.
Section Check 17.2 Question 2 The element helium has a mass number of 4 and atomic number of 2. How many neutrons are in the nucleus of a helium atom?
Answer 17.2 Section Check Recall that the atomic number is equal to the number of protons in the nucleus. Since the mass number is 4 and the atomic number is 2, there must be 2 neutrons in the nucleus of a helium atom.
Section Check 17.2 Question 3 How much of the mass of an atom is contained in an electron and what is the charge of an electron? Answer The electron’s mass is so small that it is considered negligible when finding the mass of an atom. Electrons are negative.
Atomic Mass Masses of Atoms 17.2
Organizing the Elements Periodic means "repeated in a pattern." In the late 1800s, Dmitri Mendeleev, a Russian chemist, searched for a way to organize the elements. The Periodic Table When he arranged all the elements known at that time in order of increasing atomic masses, he discovered a pattern. 17.3
Organizing the Elements Because the pattern repeated, it was considered to be periodic. Today, this arrangement is called a periodic table of elements. In the periodic table, the elements are arranged by increasing atomic number and by changes in physical and chemical properties. The Periodic Table 17.3
Mendeleev's Predictions Mendeleev had to leave blank spaces in his periodic table to keep the elements properly lined up according to their chemical properties. He looked at the properties and atomic masses of the elements surrounding these blank spaces. The Periodic Table 17.3
Mendeleev's Predictions From this information, he was able to predict the properties and the mass numbers of new elements that had not yet been discovered. The Periodic Table 17.3
Mendeleev's Predictions This table shows Mendeleev's predicted properties for germanium, which he called ekasilicon. His predictions proved to be accurate. The Periodic Table 17.3
Improving the Periodic Table On Mendeleev's table, the atomic mass gradually increased from left to right. If you look at the modern periodic table, you will see several examples, such as cobalt and nickel, where the mass decreases from left to right. The Periodic Table 17.3
Improving the Periodic Table In 1913, the work of Henry G.J. Moseley, a young English scientist, led to the arrangement of elements based on their increasing atomic numbers instead of an arrangement based on atomic masses. The Periodic Table The current periodic table uses Moseley's arrangement of the elements. 17.3
The Atom and the Periodic Table The vertical columns in the periodic table are called groups, or families, and are numbered 1 through 18. The Periodic Table Elements in each group have similar properties. 17.3
Electron Cloud Structure In a neutral atom, the number of electrons is equal to the number of protons. The Periodic Table Therefore, a carbon atom, with an atomic number of six, has six protons and six electrons. 17.3
Bohr Model Practice In atomic physics, the Bohr model, devised by Niels Bohr, depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with electrostatic forces providing attraction, rather than gravityatomic physicsNiels Bohratomnucleuselectronssolar system electrostatic forcesgravity
Examples of Bohr Models
What Element am I ?
Electron Cloud Structure Scientists have found that electrons within the electron cloud have different amounts of energy. The Periodic Table 17.3
Electron Cloud Structure The Periodic Table Scientists model the energy differences of the electrons by placing the electrons in energy levels. 17.3
Electron Cloud Structure Energy levels nearer the nucleus have lower energy than those levels that are farther away. The Periodic Table Electrons fill these energy levels from the inner levels (closer to the nucleus) to the outer levels (farther from the nucleus). 17.3
Electron Cloud Structure Elements that are in the same group have the same number of electrons in their outer energy level. The Periodic Table It is the Number of electrons in the outer energy level that determines the chemical properties of the element. 17.3
Energy Levels The maximum number of electrons that can be contained in each of the first four levels is shown. The Periodic Table 17.3
Energy Levels The Periodic Table For example, energy level one can contain a maximum of two electrons. A complete and stable outer energy level will contain eight electrons. 17.3
Rows on the Table Remember that the atomic number found on the periodic table is equal to the number of electrons in an atom. The Periodic Table 17.3
Rows on the Table The Periodic Table The first row has hydrogen with one electron and helium with two electrons both in energy level one. Energy level one can hold only two electrons. Therefore, helium has a full or complete outer energy level. 17.3
Rows on the Table The second row begins with lithium, which has three electrons—two in energy level one and one in energy level two. The Periodic Table Lithium is followed by beryllium with two outer electrons, boron with three, and so on until you reach neon with eight outer electrons. 17.3
Rows on the Table Do you notice how the row in the periodic table ends when an outer level is filled? The Periodic Table In the third row of elements, the electrons begin filling energy level three. The row ends with argon, which has a full outer energy level of eight electrons. 17.3
Electron Dot Diagrams Elements that are in the same group have the same number of electrons in their outer energy level. The Periodic Table These outer electrons are so important in determining the chemical properties of an element that a special way to represent them has been developed. 17.3
Electron Dot Diagrams An electron dot diagram uses the symbol of the element and dots to represent the electrons in the outer energy level. The Periodic Table Electron dot diagrams are used also to show how the electrons in the outer energy level are bonded when elements combine to form compounds. 17.3
Same Group—Similar Properties The elements in Group 17, the halogens, have electron dot diagrams similar to chlorine. The Periodic Table All halogens have seven electrons in their outer energy levels. 17.3
Same Group—Similar Properties A common property of the halogens is the ability to form compounds readily with elements in Group 1. The Periodic Table The Group 1 element, sodium, reacts easily with the Group 17 element, chlorine. The result is the compound sodium chloride, or NaCl—ordinary table salt. 17.3
Same Group—Similar Properties Not all elements will combine readily with other elements. The Periodic Table The elements in Group 18 have complete outer energy levels. This special configuration makes Group 18 elements relatively unreactive. 17.3
Regions on the Periodic Table The periodic table has several regions with specific names. The Periodic Table The horizontal rows of elements on the periodic table are called periods. The elements increase by one proton and one electron as you go from left to right in a period. 17.3
Regions on the Periodic Table All of the elements in the blue squares are metals. The Periodic Table 17.3
Regions on the Periodic Table The Periodic Table Those elements on the right side of the periodic table, in yellow, are classified as nonmetals. 17.3
Regions on the Periodic Table The Periodic Table The elements in green are metalloids or semimetals. 17.3
A Growing Family In 1994, scientists at the Heavy-Ion Research Laboratory in Darmstadt, Germany, discovered element 111. The Periodic Table Element 112 was discovered at the same laboratory. Both of these elements are produced in the laboratory by joining smaller atoms into a single atom. 17.3
Elements in the Universe Using the technology that is available today, scientists are finding the same elements throughout the universe. The Periodic Table Many scientists believe that hydrogen and helium are the building blocks of other elements. 17.3
Elements in the Universe Exploding stars, or supernovas, give scientists evidence to support this theory. The Periodic Table Many scientists believe that supernovas have spread the elements that are found throughout the universe. 17.3
Section Check 17.3 Question 1 How are the elements arranged in the periodic table?
Section Check 17.3 Answer The elements are arranged by increasing atomic number and by changes in physical and chemical properties.
Section Check 17.3 Question 2 What do the elements in a vertical column of the periodic table have in common?
Answer 17.3 Section Check The vertical columns in the periodic table are called groups; elements in the same group have similar properties, such as electrical conductivity.
Section Check 17.3 Question 3 What do the dots in this electron dot diagram represent?
Section Check 17.3 Answer The dots represent the electrons in the outer energy level.
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