12. Atoms & the Periodic Table

8/22/2019 12. Atoms & the Periodic Table

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© 2012 Pearson Education, Inc.

Conceptual

PhysicalScience5th Edition

Chapter 12:

ATOMS AND THEPERIODIC 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 theatom?

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.


CHECK YOUR NEIGHBOR




Which of the following are incorrect statements about theatom?

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.


CHECK 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.


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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 nucleusof 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 listedin the periodic table.

Neutrons:

• accompany protons in the nucleus

• have about the same mass as protons but nocharge, 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





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

I t d At i M




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.


CHECK YOUR NEIGHBOR

I t d At i M




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.


CHECK YOUR ANSWER

I t d At i M




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.



CHECK YOUR NEIGHBOR

I t d At i M




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.


CHECK YOUR ANSWER




The Periodic Table

• The Periodic Table is a listing of all the

known elements.




The Periodic Table


known elements.

• It is NOT something to be memorized.




The Periodic Table


known elements.


• Instead, we learn how to READ the

Periodic Table.




The Periodic Table


known elements.


• Instead, we learn how to READ the

Periodic Table.

• A chemist uses the Periodic Table muchlike a writer uses a dictionary. NEITHER

need be memorized!







The Periodic Table

• The elements are highly organized within

the Periodic Table.




The Periodic Table


the Periodic Table.

• Each vertical column is called a ―group.‖




The Periodic Table


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

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 Table

CHECK YOUR NEIGHBOR

The Periodic Table




Li F

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

A. A lithium atom

B. A fluorine atom


The Periodic Table

CHECK YOUR ANSWER

The Periodic Table




As

S

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

A. An arsenic atom

B. A sulfur atom


The Periodic Table

CHECK YOUR NEIGHBOR

The Periodic Table




As

S

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

A. An arsenic atom

B. A sulfur atom


The Periodic Table

CHECK YOUR ANSWER




Physical and Conceptual Models

• Physical model replicates the object at a

convenient scale






convenient scale

• Conceptual model describes a system






convenient scale

• 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 elementswhen 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.





Spectroscope

Atomic spectrum

is 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 amathematical formula.

• Johannes Rydberg noted that the sum of thefrequencies of two lines often equals the frequency of a third line.





Spectroscope

Spectral Lines of Various Elements





Spectroscope

Atomic Excitation





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.

Identifying Atoms Using the Spectroscope




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.

y g g p p

CHECK 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.

y g g p p

CHECK YOUR NEIGHBOR





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.

y g g p p

CHECK YOUR NEIGHBOR





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.

y g g

CHECK YOUR NEIGHBOR





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.


CHECK YOUR NEIGHBOR





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.


CHECK 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.



CHECK YOUR NEIGHBOR





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.

CHECK YOUR ANSWER







The Quantum Hypothesis

Quantum Hypothesis

Max Planck, German physicist, hypothesized—

warm bodies emit radiant energy in discrete bundlescalled 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 quantumcalled 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, dependingon 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 thefrequency 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.


CHECK YOUR NEIGHBOR





In the relationship E , the symbol stands for thefrequency 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.

CHECK YOUR NEIGHBOR

The Quantum HypothesisCHECK YOUR NEIGHBOR




Which of these has the greatest energy per photon? A. Red light.

B. Green light.

C. Blue light.

D. All have the same.

CHECK YOUR NEIGHBOR

The Quantum HypothesisCHECK YOUR ANSWER




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 greatestenergy per photon.

CHECK YOUR ANSWER





Which of these photons has the smallest energy? A. Infrared.

B. Visible.

C. Ultraviolet.


CHECK YOUR NEIGHBOR





Which of these photons has the smallest energy? A. Infrared.

B. Visible.

C. Ultraviolet.


Explanation:

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

CHECK YOUR ANSWER





Using the quantum hypothesis:

• Danish physicist Niels Bohr explained the

formation of atomic spectra as follows:

—The potential energy of an electron depends on itsdistance from the nucleus.

—When an atom absorbs a photon of light, it

absorbs energy. Then a low-potential-energyelectron 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

CHECK YOUR NEIGHBOR





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.

CHECK YOUR ANSWER





Bohr’s model explains why atoms don’t

collapse:

• Electrons can lose only specific amounts of

energy equivalent to transitions betweenlevels.

• 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 emittedphoton 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 inon 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

Documents

12. Atoms & the Periodic Table