12 lecture outline-2
TRANSCRIPT
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Hewitt/Suchocki/Hewitt Conceptual Physical Science
Fourth Edition
Chapter 12:
ATOMS AND THE PERIODIC TABLE
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This lecture will help you understand:
• Atoms Are Ancient and Empty• The Elements• Protons and Neutrons• The Periodic Table• Periods and Groups• Physical and Conceptual Models• Identifying Atoms Using the Spectroscope• The Quantum Hypothesis• Electron Waves• The Shell Model
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Atoms Are Ancient and Empty
Atoms are • ancient
—origin of most atoms goes back to birth of universe
• mostly empty space
Elements heavier than hydrogen and much of the helium were produced in the interiors of stars.
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Which of the following are incorrect statements about the atom?
A. Atoms have been around since the beginning of the universe.
B. Atoms are mostly empty space.
C. Atoms are perpetually moving.
D. Atoms are manufactured in plants, and in humans during pregnancy.
Atoms Are Ancient and EmptyCHECK YOUR NEIGHBOR
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Which of the following are incorrect statements about the atom?
A. Atoms have been around since the beginning of the universe.
B. Atoms are mostly empty space.
C. Atoms are perpetually moving.
D. Atoms are manufactured in plants, and in humans during pregnancy.
Atoms Are Ancient and EmptyCHECK YOUR ANSWER
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The Elements
• Element: A material made of only one kind of atom. Pure gold is an example as it is made of only gold atoms.
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The Elements
• Element: A material made of only one kind of atom. Pure gold is an example as it is made of only gold atoms.
• Atom: The fundamental unit of an element.
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The Elements
• Element: A material made of only one kind of atom. Pure gold is an example as it is made of only gold atoms.
• Atom: The fundamental unit of an element.
The term “element” is used when referring to macroscopic quantities.
The term “atom” is used when discussing the submicroscopic.
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The Elements
Atoms: • make up all matter around us• to date, 115 distinct kinds of atoms—
90 found in nature, remainder synthesized
Element
any material consisting of only one type of atom
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Protons and Neutrons
Protons:• carry a positive charge—same quantity of
charge as electrons• are about 1800 times as massive as an
electron• have the same number of protons in the
nucleus as electrons surrounding the nucleus of an electrically neutral atom
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Protons and Neutrons
Electrons:• are identical• repel electrons of neighboring atoms• have electrical repulsion that prevents atomic
closeness
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Protons and Neutrons
Atomic number:is the number of protons in each element listed in the periodic table.
Neutrons:• accompany protons in the nucleus• have about the same mass as protons but no
charge, so are electrically neutral
Both protons and neutrons are nucleons.
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Isotopes and Atomic Mass
Isotopes:• refers to atoms of the same element that contain the
same number of protons but different numbers of neutrons in the nucleus
• identified by mass number, which is the total number of protons and neutrons in the nucleus
• differ only in mass and not by electric charge; therefore, isotopes share many characteristics
Total number of neutrons in isotope = mass number – atomic number
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Isotopes and Atomic Mass
Atomic mass:• total mass of the atom(s) [protons, neutrons,
and electrons]• listed in periodic table as atomic mass unit
One atomic mass unit is equal to
1.661 10–24 gram or 1.661 10–27 kg
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The atomic number of an element matches the number of
A. protons in the nucleus of an atom.
B. electrons in a neutral atom.
C. both of the above.
D. none of the above.
Isotopes and Atomic MassCHECK YOUR NEIGHBOR
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The atomic number of an element matches the number of
A. protons in the nucleus of an atom.
B. electrons in a neutral atom.
C. both of the above.
D. none of the above.
Comment:
When the atomic number doesn’t match the number of electrons, the atom is an ion.
Isotopes and Atomic MassCHECK YOUR ANSWER
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A nucleus with an atomic number of 44 and a mass number of 100 must have
A. 44 neutrons.
B. 56 neutrons.
C. 100 neutrons.
D. none of the above.
Isotopes and Atomic MassCHECK YOUR NEIGHBOR
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A nucleus with an atomic number of 44 and a mass number of 100 must have
A. 44 neutrons.
B. 56 neutrons.
C. 100 neutrons.
D. none of the above.
Comment:
Be sure to distinguish between neutron and nucleon. Of the
100 nucleons in the nucleus, 56 are neutrons. A neutron is a nucleon, as is a proton.
Isotopes and Atomic MassCHECK YOUR ANSWER
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The Periodic Table
• The Periodic Table is a listing of all the known elements.
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The Periodic Table
• The Periodic Table is a listing of all the known elements.
• It is NOT something to be memorized.
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The Periodic Table
• The Periodic Table is a listing of all the known elements.
• It is NOT something to be memorized.
• Instead, we learn how to READ the Periodic Table.
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The Periodic Table
• The Periodic Table is a listing of all the known elements.
• It is NOT something to be memorized.
• Instead, we learn how to READ the Periodic Table.
• A chemist uses the Periodic Table much like a writer uses a dictionary. NEITHER need be memorized!
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The Periodic Table
• The elements are highly organized within the Periodic Table.
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The Periodic Table
• The elements are highly organized within the Periodic Table.
• Each vertical column is called a “group.”
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The Periodic Table
• The elements are highly organized within the Periodic Table.
• Each vertical column is called a “group.”
• Each horizontal row is called a “period.”
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The Periodic Table
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The Periodic Table
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The Periodic Table
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The Periodic Table
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Li F
Which is larger: a lithium atom or a fluorine atom?
A. A lithium atom
B. A fluorine atom
C. There is no way to tell without memorizing the periodic table.
The Periodic TableCHECK YOUR NEIGHBOR
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Li F
Which is larger: a lithium atom or a fluorine atom?
A. A lithium atom
B. A fluorine atom
C. There is no way to tell without memorizing the periodic table.
The Periodic TableCHECK YOUR ANSWER
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As
S
Which is larger: an arsenic atom or a sulfur atom?
A. An arsenic atom
B. A sulfur atom
C. There is no way to tell without memorizing the periodic table.
The Periodic TableCHECK YOUR NEIGHBOR
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As
S
Which is larger: an arsenic atom or a sulfur atom?
A. An arsenic atom
B. A sulfur atom
C. There is no way to tell without memorizing the periodic table.
The Periodic TableCHECK YOUR ANSWER
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Physical and Conceptual Models
• Physical model replicates the object at a convenient scale
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Physical and Conceptual Models
• Physical model replicates the object at a convenient scale
• Conceptual model describes a system
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Physical and Conceptual Models
• Physical model replicates the object at a convenient scale
• Conceptual model describes a system
-An atom is best described by a conceptual model.
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Identifying Atoms Using the Spectroscope
Spectroscope:• an instrument that separates and spreads
light into its component frequencies• allows analysis of light emitted by elements
when they are made to glow—identifies each element by its characteristic pattern
Each element emits a distinctive glow when energized and displays a distinctive spectrum.
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Identifying Atoms Using the Spectroscope
Atomic spectrumis an element’s fingerprint—a pattern of discrete (distinct) frequencies of light.
Discoveries of atomic spectrum of hydrogen:• A researcher in the 1800s noted that hydrogen has a
more orderly atomic spectrum than others.• Johann Balmer expressed line positions by a
mathematical formula.• Johannes Rydberg noted that the sum of the
frequencies of two lines often equals the frequency of a third line.
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Identifying Atoms Using the Spectroscope
Spectral Lines of Various Elements
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Identifying Atoms Using the Spectroscope
Atomic Excitation
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Identifying Atoms Using the Spectroscope
Three transitions in an atom. The sum of the energies (and frequencies) for jumps A and B equals the energy (and frequency) of jump C.
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Each spectral line in an atomic spectrum represents
A. a specific frequency of light emitted by an element.
B. one of the many colors of an element.
C. a pattern characteristic of the element.
D. all of the above.
Identifying Atoms Using the SpectroscopeCHECK YOUR NEIGHBOR
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Each spectral line in an atomic spectrum represents
A. a specific frequency of light emitted by an element.
B. one of the many colors of an element.
C. a pattern characteristic of the element.
D. all of the above.
Explanation:
Many lines make up a pattern that is characteristic of the element, so choice C doesn’t fly. Interestingly, the line shape of each spectral line is an image of a thin slit in the spectroscope.
Identifying Atoms Using the SpectroscopeCHECK YOUR NEIGHBOR
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The hydrogen spectrum consists of many spectral lines. How can this simple element have so many lines?
A. One electron can be boosted to many different energy levels.
B. The electron can move at a variety of speeds.
C. The electron can vibrate at a variety of frequencies.
D. Many standing electron waves can fit in the shell of the hydrogen atom.
Identifying Atoms Using the SpectroscopeCHECK YOUR NEIGHBOR
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The hydrogen spectrum consists of many spectral lines. How can this simple element have so many lines?
A. One electron can be boosted to many different energy levels.
B. The electron can move at a variety of speeds.
C. The electron can vibrate at a variety of frequencies.
D. Many standing electron waves can fit in the shell of the hydrogen atom.
Identifying Atoms Using the SpectroscopeCHECK YOUR NEIGHBOR
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When an atom is excited, its
A. electrons are boosted to higher energy levels.
B. atoms are charged with light energy.
C. atoms are made to shake, rattle, and roll.
D. none of the above.
Identifying Atoms Using the SpectroscopeCHECK YOUR NEIGHBOR
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When an atom is excited, its
A. electrons are boosted to higher energy levels.
B. atoms are charged with light energy.
C. atoms are made to shake, rattle, and roll.
D. none of the above.
Identifying Atoms Using the SpectroscopeCHECK YOUR ANSWER
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The frequencies of light emitted by an atom often add up to
A. a higher frequency of light emitted by the same atom.
B. a lower frequency of light emitted by the same atom.
C. both of the above.
D. none of the above.
Identifying Atoms Using the SpectroscopeCHECK YOUR NEIGHBOR
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The frequencies of light emitted by an atom often add up to
A. a higher frequency of light emitted by the same atom.
B. a lower frequency of light emitted by the same atom.
C. both of the above.
D. none of the above.
Explanation:This follows from two energy transitions in an atom summing to equal another energy transition. See the next slide.
Identifying Atoms Using the SpectroscopeCHECK YOUR ANSWER
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The Quantum Hypothesis
Quantum HypothesisMax Planck, German physicist, hypothesized—warm bodies emit radiant energy in discrete bundles called quanta. Energy in each energy bundle is proportional to the frequency of radiation.
Einstein stated that light itself is quantized. A beam of light is not a continuous stream of energy but consists of countless small discrete quanta of energy, each quantum called a photon.
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The Quantum Hypothesis
Is light a wave, or a stream of particles?
Light can be described by both models—it exhibits properties of both a wave or a particle, depending on the experiment.
The amount of energy in a photon is directly proportional to the frequency of light:
E
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In the relationship E , the symbol stands for the frequency of emitted light, and E stands for the
A. potential energy of the electron emitting the light.
B. energy of the photon.
C. kinetic energy of the photon.
D. all of the above.
The Quantum HypothesisCHECK YOUR NEIGHBOR
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In the relationship E , the symbol stands for the frequency of emitted light, and E stands for the
A. potential energy of the electron emitting the light.
B. energy of the photon.
C. kinetic energy of the photon.
D. all of the above.
Explanation:
For those answering choice A, note that the energy of the photon is equal to the difference in energy levels for the electron emitting the photon—not its value at one energy level.
The Quantum HypothesisCHECK YOUR NEIGHBOR
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Which of these has the greatest energy per photon?
A. Red light.
B. Green light.
C. Blue light.
D. All have the same.
The Quantum HypothesisCHECK YOUR NEIGHBOR
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Which of these has the greatest energy per photon?
A. Red light.
B. Green light.
C. Blue light.
D. All have the same.
Explanation:
In accord with E , the highest frequency light has the greatest energy per photon.
The Quantum HypothesisCHECK YOUR ANSWER
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Which of these photons has the smallest energy?
A. Infrared.
B. Visible.
C. Ultraviolet.
D. All have the same.
The Quantum HypothesisCHECK YOUR NEIGHBOR
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Which of these photons has the smallest energy?
A. Infrared.
B. Visible.
C. Ultraviolet.
D. All have the same.
Explanation:
In accord with E , the lowest frequency radiation has the smallest energy per photon.
The Quantum HypothesisCHECK YOUR ANSWER
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The Quantum Hypothesis
Using the quantum hypothesis:• Danish physicist Niels Bohr explained the
formation of atomic spectra as follows:—The potential energy of an electron depends on its
distance from the nucleus.
—When an atom absorbs a photon of light, it absorbs energy. Then a low-potential-energy electron is boosted to become a high-potential-energy electron.
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The Quantum Hypothesis
Using quantum hypothesis:• When an electron in any energy level drops closer to
the nucleus, it emits a photon of light.• Bohr reasoned that there must be a number of distinct
energy levels within the atom. Each energy level has a principal quantum number n, where n is always an integer. The lowest level is n = 1 and is closest to the nucleus.
Electrons release energy in discrete amounts that form discrete lines in the atom’s spectrum.
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Which of the following is a quantum number?
A. 0.02
B. 0.2
C. 2
D. 2.5
The Quantum HypothesisCHECK YOUR NEIGHBOR
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Which of the following is a quantum number?
A. 0.02
B. 0.2
C. 2
D. 2.5
Explanation:
Quantum numbers are integers only.
The Quantum HypothesisCHECK YOUR ANSWER
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The Quantum Hypothesis
Bohr’s model explains why atoms don’t collapse:• Electrons can lose only specific amounts of
energy equivalent to transitions between levels.
• An atom reaches the lowest energy level called the ground state, where the electron can’t lose more energy and can’t move closer to the nucleus.
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The Quantum Hypothesis
Planetary model of the atom:Photons are emitted by atoms as electrons move from higher-energy outer levels to lower-energy inner levels. The energy of an emitted photon is equal to the difference in energy between the two levels. Because an electron is restricted to discrete levels, only lights of distinct frequencies are emitted.
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Electron Waves
An electron’s wave nature explains why electrons in an atom are restricted to particular energy levels. Permitted energy levels are a natural consequence of standing electron waves closing in on themselves in a synchronized manner.
The orbit for n = 1 consists of a single wavelength, n = 2 is of two wavelengths, and so on.
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Electron Waves
For a fixed circumference, only an integral number of standing waves can occur, and likewise in the paths of electrons about the nucleus.
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The Shell Model
Cutaway view of shells in the shell model of the atom
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The Shell Model
Shell model showing the first three periods of the periodic table