12 lecture outline-2

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley

Hewitt/Suchocki/Hewitt Conceptual Physical Science

Fourth Edition

Chapter 12:

ATOMS AND THE PERIODIC TABLE


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


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.


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


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


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.


The Elements


• Atom: The fundamental unit of an element.


The Elements


• 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.


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


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



Electrons:• are identical• repel electrons of neighboring atoms• have electrical repulsion that prevents atomic

closeness



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.


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


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


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


The atomic number of an element matches the number of

A. protons in the nucleus of an atom.

B. electrons in a neutral atom.



Comment:

When the atomic number doesn’t match the number of electrons, the atom is an ion.

Isotopes and Atomic MassCHECK YOUR ANSWER


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.


Isotopes and Atomic MassCHECK YOUR NEIGHBOR


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.


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


The Periodic Table

• The Periodic Table is a listing of all the known elements.


The Periodic Table


• It is NOT something to be memorized.


The Periodic Table



• Instead, we learn how to READ the Periodic Table.


The Periodic Table



• 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!



The Periodic Table

• The elements are highly organized within the Periodic Table.


The Periodic Table


• Each vertical column is called a “group.”


The Periodic Table


• Each vertical column is called a “group.”

• Each horizontal row is called a “period.”


The Periodic Table


The Periodic Table


The Periodic Table


The Periodic Table


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


Li F

Which is larger: a lithium atom or a fluorine atom?

A. A lithium atom

B. A fluorine atom


The Periodic TableCHECK YOUR ANSWER


As

S

Which is larger: an arsenic atom or a sulfur atom?

A. An arsenic atom

B. A sulfur atom


The Periodic TableCHECK YOUR NEIGHBOR


As

S

Which is larger: an arsenic atom or a sulfur atom?

A. An arsenic atom

B. A sulfur atom


The Periodic TableCHECK YOUR ANSWER


Physical and Conceptual Models

• Physical model replicates the object at a convenient scale




• Conceptual model describes a system




• Conceptual model describes a system

-An atom is best described by a conceptual model.


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.



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.



Spectral Lines of Various Elements



Atomic Excitation



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.


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


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.


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.



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.



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.



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.




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.


Identifying Atoms Using the SpectroscopeCHECK YOUR ANSWER


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.





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.



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



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.



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


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.


The Quantum HypothesisCHECK YOUR NEIGHBOR


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.


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.



Which of these has the greatest energy per photon?

A. Red light.

B. Green light.

C. Blue light.

D. All have the same.



Which of these has the greatest energy per photon?

A. Red light.

B. Green light.

C. Blue light.


Explanation:

In accord with E , the highest frequency light has the greatest energy per photon.

The Quantum HypothesisCHECK YOUR ANSWER


Which of these photons has the smallest energy?

A. Infrared.

B. Visible.

C. Ultraviolet.




Which of these photons has the smallest energy?

A. Infrared.

B. Visible.

C. Ultraviolet.


Explanation:

In accord with E , the lowest frequency radiation has the smallest energy per photon.




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.



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.


Which of the following is a quantum number?

A. 0.02

B. 0.2

C. 2

D. 2.5



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.




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.



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.


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.


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.


The Shell Model

Cutaway view of shells in the shell model of the atom


The Shell Model

Shell model showing the first three periods of the periodic table

Technology

12 lecture outline-2