chapter 9 lecture conceptual integrated science second edition © 2013 pearson education, inc. atoms...

Chapter 9 Lecture

ConceptualIntegrated Science

Second Edition

© 2013 Pearson Education, Inc.

Atoms and the Periodic Table


This lecture will help you understand:

• Atoms Are Ancient and Empty• The Elements• Protons and Neutrons• Isotopes and Atomic Mass• The Periodic Table• 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.

• The origin of most atoms goes back to the birth of the universe.

– mostly empty space.

• Elements heavier than hydrogen and much of the helium were produced in the interiors of stars.


Atoms Are Ancient and EmptyCHECK YOUR NEIGHBORWhich of these statements about the atom are incorrect?

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.

Explain your answer to your neighbor.


Atoms Are Ancient and EmptyCHECK YOUR ANSWER

Which of these statements about the atom areincorrect?

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.


The Elements

• An element is a material made of only one kind of atom. For example, pure gold is an element because it is made of only gold atoms.

• An atom is 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: – Atoms make up all matter around us.– To date, 115 distinct kinds of atoms are

known—90 are found in nature, and the rest are synthesized.

• An element is any material that consists of only one type of atom.


Protons and Neutrons

• Protons– carry a positive charge—the same quantity of

charge as electrons.– are about 1800 times as massive as

electrons.– have the same number of protons in the

nucleus as electrons that surround the nucleus of an electrically neutral atom.



• Electrons– are identical.– repel the electrons of neighboring atoms.– have electrical repulsion that prevents atomic

closeness.



• The 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 they are electrically neutral.

• Both protons and neutrons are nucleons.


Isotopes and Atomic Mass

• Isotopes– are atoms of the same element that contain the same

number of protons but different numbers of neutrons in the nucleus.

– are identified by mass number, which is the total number of protons and neutrons in the nucleus.

– differ only in mass, not electric charge; therefore, isotopes share many characteristics.

• Total number of neutrons in isotope:Mass number atomic number


Isotopes and Atomic Mass

• Atomic mass is– the total mass of the atom(s) [protons,

neutrons, and electrons].– listed in the periodic table in atomic mass

units.

• One atomic mass unit is equal to1.661 10–24 gram or 1.661 10–27 kg.


Isotopes and Atomic MassCHECK YOUR NEIGHBORThe 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 aboveD. none of the above



Isotopes and Atomic MassCHECK YOUR ANSWERThe 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 aboveD. 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 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.

D. none of the above



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.


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.


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 as a

writer uses a dictionary. NEITHER needs be memorized!


The Periodic Table


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.


The Periodic Table


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

A. A lithium atomB. A fluorine atomC. 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 atomB. A fluorine atomC. There is no way to tell without memorizing the periodic

table.

The Periodic TableCHECK YOUR ANSWER

Li F


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

A. An arsenic atomB. A sulfur atomC. There is no way to tell without memorizing the periodic table.


The Periodic TableCHECK YOUR NEIGHBOR

As

S


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

A. An arsenic atomB. A sulfur atomC. There is no way to tell without memorizing the periodic table.

The Periodic TableCHECK YOUR ANSWER

As

S


• A physical model replicates an object at a convenient scale.

• A conceptual model describes a system.– An atom is best described by a conceptual

model.

Physical and Conceptual Models


• A spectroscope– is an instrument that separates and spreads

light into its component frequencies.– allows the analysis of light emitted by

elements when they are made to glow. It identifies each element by its characteristic pattern.

– Each element emits a distinctive glow when energized and displays a distinctive spectrum.

Identifying Atoms Using the Spectroscope


• An atomic spectrum is an element's fingerprint—a pattern of discrete (distinct) frequencies of light.

• Discoveries of the 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



• There are three transitions in an atom. The sum of the energies (and frequencies) for jumps A and B equals the energy (and frequency) for jump C.



Identifying Atoms Using the SpectroscopeCHECK YOUR NEIGHBOREach 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 ANSWEREach 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 NEIGHBORThe 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 ANSWERThe 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

When an atom is excited, its

A. electrons are boosted to higher energylevels.

B. atoms are charged with light energy.

C. atoms are made to shake, rattle, and roll.




Identifying Atoms Using the SpectroscopeCHECK YOUR ANSWER

When an atom is excited, its

A. electrons are boosted to higher energylevels.

B. atoms are charged with light energy.

C. atoms are made to shake, rattle, and roll.



Identifying Atoms Using the SpectroscopeCHECK YOUR NEIGHBORThe 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 aboveD. none of the above



Identifying Atoms Using the SpectroscopeCHECK YOUR ANSWERThe 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 aboveD. none of the above

Explanation:This answer follows from the fact that two energy transitions in an atom sum to equal another energy transition. See the next slide.


The Quantum Hypothesis

• Max Planck, a German physicist, hypothesized that warm bodies emit radiant energy in discrete bundles called quanta. The energy in each energy bundle is proportional to the frequency of the 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, with 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 and a particle, depending on the experiment.

• The amount of energy in a photon is directly proportional to the frequency of light:

E


The Quantum HypothesisCHECK YOUR NEIGHBORIn 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 ANSWERIn 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

Which of these has the most energy per photon?

A. Red light

B. Green light

C. Blue light

D. All have the same.



The Quantum HypothesisCHECK YOUR ANSWER

Which of these has the most energy per photon?

A. Red light

B. Green light

C. Blue light


Explanation:

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


The Quantum HypothesisCHECK YOUR NEIGHBOR

Which of these photons has the least energy?

A. Infrared

B. Visible

C. Ultraviolet





Which of these photons has the least energy?

A. Infrared

B. Visible

C. Ultraviolet


Explanation:

In accord with E , the lowest frequency radiation has the least 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 the quantum hypothesis (continued):– 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. The 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 of two wavelengths, and so on.


Electron Waves

• For a fixed circumference, only an integral number of standing waves can occur, and likewise for 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

chapter 9 lecture conceptual integrated science second edition © 2013 pearson education, inc. atoms...

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