Transcript PP Chapter 9 Text

Hewitt/Lyons/Suchocki/Yeh
Conceptual Integrated
Science
Chapter 9
THE ATOM
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
This lecture will help you
understand:
•
•
•
•
•
•
•
•
•
The Elements
The Periodic Table
Atoms Are Ancient, Tiny, and Empty
Protons and Neutrons
Isotopes and Atomic Mass
Atomic Spectra
The Quantum Hypothesis
Electron Waves
Probability Clouds and Atomic Orbitals
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
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
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
The Periodic Table
Periodic table:
• list of chemical elements
• designates each element by its atomic
symbol—first letter is capitalized
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Atoms Are Ancient, Tiny, and Empty
Atoms are
• ancient
—origin of most atoms goes back to birth of universe
• tiny
—first and lightest atom making up 90% of the
universe is hydrogen, H, followed by He
—in perpetual motion
—so small that when you inhale, you breathe atoms
that were once part of every person who ever lived
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Atoms Are Ancient, Tiny, and Empty
Atoms are
• tiny
—can’t be seen with visible light—smaller than the wavelength
of visible light
—made up of subatomic particles, protons and neutrons, in a
central nucleus surrounded by electrons
• mostly empty space
Elements heavier than hydrogen and much of the helium were
produced in the interiors of stars.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Atoms Are Ancient, Tiny, and Empty
CHECK YOUR NEIGHBOR
Which of the following are incorrect statements about the
atom?
A.
B.
C.
D.
Atoms are smaller than the wavelength of visible light.
Atoms are mostly empty space, just as the solar system is mostly
empty space.
Atoms are perpetually moving.
Atoms are manufactured in plants, and in humans during
pregnancy.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Atoms Are Ancient, Tiny, and Empty
CHECK YOUR ANSWER
Which of the following are incorrect statements about the
atom?
A.
B.
C.
D.
Atoms are smaller than the wavelength of visible light.
Atoms are mostly empty space, just as the solar system is mostly
empty space.
Atoms are perpetually moving.
Atoms are manufactured in plants, and in humans during
pregnancy.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
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
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Protons and Neutrons
Electrons:
• are identical
• repel electrons of neighboring atoms
• have electrical repulsion that prevents atomic
closeness
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
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.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
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
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
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
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Isotopes and Atomic Mass
CHECK YOUR NEIGHBOR
The atomic number of an element matches the number of
A.
B.
C.
D.
protons in the nucleus of an atom.
electrons in a neutral atom.
both of the above.
none of the above.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Isotopes and Atomic Mass
CHECK YOUR ANSWER
The atomic number of an element matches the number of
A.
B.
C.
D.
protons in the nucleus of an atom.
electrons in a neutral atom.
both of the above.
none of the above.
Comment:
When the atomic number doesn’t match the number of electrons,
the atom is an ion.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Isotopes and Atomic Mass
CHECK YOUR NEIGHBOR
A nucleus with an atomic number of 44 and a mass number
of 100 must have
A.
B.
C.
D.
44 neutrons.
56 neutrons.
100 neutrons.
none of the above.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Isotopes and Atomic Mass
CHECK YOUR ANSWER
A nucleus with an atomic number of 44 and a mass number
of 100 must have
A.
B.
C.
D.
44 neutrons.
56 neutrons.
100 neutrons.
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.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Atomic Spectra
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.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Atomic Spectra
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 a
mathematical formula.
• Johannes Rydberg noted that the sum of the
frequencies of two lines often equals the frequency of
a third line.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Atomic Spectra
Spectral Lines of Various Elements
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Atomic Spectra
Atomic Excitation
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Atomic Spectra
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.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Atomic Spectra
CHECK YOUR NEIGHBOR
Each spectral line in an atomic spectrum represents
A.
B.
C.
D.
a specific frequency of light emitted by an element.
one of the many colors of an element.
a pattern characteristic of the element.
all of the above.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Atomic Spectra
CHECK YOUR ANSWER
Each spectral line in an atomic spectrum represents
A.
B.
C.
D.
a specific frequency of light emitted by an element.
one of the many colors of an element.
a pattern characteristic of the element.
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.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Atomic Spectra
CHECK YOUR NEIGHBOR
The hydrogen spectrum consists of many spectral lines.
How can this simple element have so many lines?
A.
B.
C.
D.
One electron can be boosted to many different energy levels.
The electron can move at a variety of speeds.
The electron can vibrate at a variety of frequencies.
Many standing electron waves can fit in the shell of the hydrogen
atom.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Atomic Spectra
CHECK YOUR ANSWER
The hydrogen spectrum consists of many spectral lines.
How can this simple element have so many lines?
A.
B.
C.
D.
One electron can be boosted to many different energy levels.
The electron can move at a variety of speeds.
The electron can vibrate at a variety of frequencies.
Many standing electron waves can fit in the shell of the hydrogen
atom.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Atomic Spectra
CHECK YOUR NEIGHBOR
When an atom is excited, its
A.
B.
C.
D.
electrons are boosted to higher energy levels.
atoms are charged with light energy.
atoms are made to shake, rattle, and roll.
none of the above.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Atomic Spectra
CHECK YOUR ANSWER
When an atom is excited, its
A.
B.
C.
D.
electrons are boosted to higher energy levels.
atoms are charged with light energy.
atoms are made to shake, rattle, and roll.
none of the above.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Atomic Spectra
CHECK YOUR NEIGHBOR
The frequencies of light emitted by an atom often add up to
equal
A.
B.
C.
D.
a higher frequency of light emitted by the same atom.
a lower frequency of light emitted by the same atom.
both of the above.
none of the above.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Atomic Spectra
CHECK YOUR ANSWER
The frequencies of light emitted by an atom often add up to
equal
A.
B.
C.
D.
a higher frequency of light emitted by the same atom.
a lower frequency of light emitted by the same atom.
both of the above.
none of the above.
Explanation:
This follows from two energy transitions in an atom summing to
equal another energy transition. See Figure 9.20.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
The Quantum Hypothesis
Quantum Hypothesis
Max 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.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
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
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
The Quantum Hypothesis
CHECK YOUR NEIGHBOR
In the relationship E  , the symbol  stands for the
frequency of emitted light, and E stands for the
A.
B.
C.
D.
potential energy of the electron emitting the light.
energy of the photon.
kinetic energy of the photon.
all of the above.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
The Quantum Hypothesis
CHECK YOUR ANSWER
In the relationship E  , the symbol  stands for the
frequency of emitted light, and E stands for the
A.
B.
C.
D.
potential energy of the electron emitting the light.
energy of the photon.
kinetic energy of the photon.
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.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
The Quantum Hypothesis
CHECK YOUR NEIGHBOR
Which of these has the greatest energy per photon?
A.
B.
C.
D.
Red light.
Green light.
Blue light.
All have the same.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
The Quantum Hypothesis
CHECK YOUR ANSWER
Which of these has the greatest energy per photon?
A.
B.
C.
D.
Red light.
Green light.
Blue light.
All have the same.
Explanation:
In accord with E  , the highest frequency light has the greatest
energy per photon.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
The Quantum Hypothesis
CHECK YOUR NEIGHBOR
Which of these photons has the smallest energy?
A.
B.
C.
D.
Infrared.
Visible.
Ultraviolet.
All have the same.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
The Quantum Hypothesis
CHECK YOUR ANSWER
Which of these photons has the smallest energy?
A.
B.
C.
D.
Infrared.
Visible.
Ultraviolet.
All have the same.
Explanation:
In accord with E  , the lowest frequency radiation has the
smallest energy per photon.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
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-potentialenergy electron.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
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.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
The Quantum Hypothesis
CHECK YOUR NEIGHBOR
Which of the following is a quantum number?
A.
B.
C.
D.
0.02
0.2
2
2.5
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
The Quantum Hypothesis
CHECK YOUR ANSWER
Which of the following is a quantum number?
A.
B.
C.
D.
0.02
0.2
2
2.5
Explanation:
Quantum numbers are integers only.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
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.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
The Quantum Hypothesis
Planetary model of the atom:
Photons are emitted by atoms as electrons
move from higher-energy outer levels to lowerenergy 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.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
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.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
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.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Probability Clouds and Atomic Orbitals
Three-dimensional electron waves:
• They comprise a probability cloud.
• They are more intense in some regions than
in others.
• Erwin Schrödinger, Austrian scientist,
formulated an equation from which intensities
of electron waves in an atom can be
calculated.
• The Schrödinger wave equation describes the
probability of finding the electron at various
locations in the atom.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Probability Clouds and Atomic Orbitals
The densest regions correspond to where
the electron’s wave intensity is greatest.
The probability cloud is a close
approximation to the actual shape of an
electron’s three-dimensional wave.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Probability Clouds and Atomic Orbitals
Atomic orbitals:
• They are simply a volume of space within
which an electron may reside.
• Each orbital represents a different region in
which an electron of a given energy is most
likely to be found.
• They are classified by letters s, p, d, and f and
come in a variety of shapes.
• Electron energies are quantized, and the
sizes of atomic orbitals are quantized.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Probability Clouds and Atomic Orbitals
s, p, d, and f Orbitals
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Probability Clouds and Atomic Orbitals
Cutaway view of shells in the shell model of the
atom
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley
Probability Clouds and Atomic Orbitals
Shell model showing the first three periods of the
periodic table
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley