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Chapter 10
The amazing
colors in
these
fireworks
explosions
are the result
of electrons
transferring
between
energy levels
in atoms.
Chapter Outline
10.1 A Brief History
10.2 Electromagnetic
Radiation
10.3 The Bohr Atom
10.5 Atomic Structures of the
First 18 Elements
10.6 Electron Structures and
the Periodic Table
10.4 Energy Levels of
Electrons
Copyright 2012 John Wiley & Sons, Inc
10-2
Objectives for Today



Historical models of the atom
Electromagnetic radiation & the atom
Electron configurations
10-3
Democritus
• Greek natural philosopher
• Concept of “Atomos”
4
Dalton’s Atomic Theory
In Dalton’s atomic theory, atoms
• are tiny particles of matter.
• of an element are similar and different
from other elements.
• of two or more different elements
combine to form compounds.
• are rearranged to form new
combinations in a chemical reaction.
5
Rutherford’s Gold Foil Experiment
Copyright © 2009 by Pearson Education, Inc.
6
Rutherford’s Gold Foil Experiment
In Rutherford’s gold foil experiment,
positively charged particles were aimed at
atoms of gold.
Most went straight through the atoms.
A few were deflected.
Conclusion:
There must be a small, dense, positively
charged nucleus in the atom that deflects
positive particles that come close.
7
Atoms
• Tiny…about 10-10 m
– If the atoms in your body were 1 in. in diameter,
you’d bump your head on the moon.
• Huge number of atoms in even a small
sample of an element
– 1/2 carat diamond has 5  1021 atoms…if lined up,
would stretch to the sun.
Electromagnetic Radiation
Frequency tells how many waves pass a particular
point per second.
Speed tells how fast a wave moves through space.
Figure 10.1 The wavelength of this wave is shown
by λ. It can be measured from peak to peak or
trough to trough.
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10-9
The Electromagnetic Spectrum
Visible light is only a small part of the
electromagnetic spectrum.
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10-10
Your Turn!
• The number of waves that pass a particular
point per second is known as
a. Frequency
b. Wavelength
c. Amplitude
d. Speed
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10-11
Your Turn!
• The color of visible light is determined by its
a. Speed
b. Wavelength
c. Amplitude
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10-12
Bohr Model (1912-1913)
• Danish physicist Niels Bohr
proposed that electrons in
an atom are organized into
discrete energy levels.
• He pictured the negative
electrons in orbits around
the positive nucleus.
• His evidence: the line
spectra of the elements.
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10-13
Line Spectrum
• Atoms absorb energy to give off light..
• Prisms or diffraction gratings separate the
light into a line spectrum for the element.
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10-14
Line Spectrum
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10-15
Why so many lines?
Absorbed
energy
5
4
3
Released
energy
2
Each line in the spectrum corresponds to
electrons moving from a higher energy
level to a lower energy level.
1
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10-16
Your Turn!
• The lowest possible energy level for an
electron is known as
a. Low state
b. Ground state
c. Basement state
d. Excited state
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10-17
Bohr Model
• Was based on electrons having fixed energy
levels and therefore quantized amounts of
energy.
• Accounted for spectral lines.
• Worked very well for hydrogen but did not
work well for heavier atoms.
• Another model is needed that describes the
behavior of electrons as waves.
Copyright 2012 John Wiley & Sons, Inc
10-18
Ways to deal with Complexity and
Uncertainty
• Analogies In order to communicate something of
the nature of the electron, scientists often use
analogies. For example, in some ways, electrons are
like vibrating guitar strings.
• Probabilities In order to accommodate the
uncertainty of the electron’s position and motion,
we refer to where the electron probably is within
the atom instead of where it definitely is.
Guitar String Waveform
Allowed
Vibrations
for a
Guitar
String
Wave Character of the
Electron
• Just as the intensity of the movement of a
guitar string can vary, so can the intensity of the
negative charge of the electron vary at different
positions outside the nucleus.
• The variation in the intensity of the electron
charge can be described in terms of a threedimensional standing wave like the standing
wave of the guitar string.
Wave Character of the
Electron
• Although both the electron and the guitar
string can have an infinite number of
possible waveforms, only certain waveforms
are possible.
• We can focus our attention on the waveform
of varying charge intensity without having to
think about the actual physical nature of the
electron.
Waveform for 1s Electron
The Wave-Mechanical Model
• This mathematical model
of the atom describes the
energy of the electron
with some certainty, but
the actual location of the
electron is uncertain.
• An orbital is the region in
space where there is a
high probability of finding
an electron with a given
energy.
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1s Orbital
Particle Interpretation of 1s
Orbital
Energy Levels of Electrons
• Electrons in atoms are
organized into discrete
principal energy levels (n,
where n is an integer).
• Lowest energy level is n = 1,
then n = 2, etc.
• As n increases, the energy
of the electron increases,
and the electron is on
average further from the
nucleus.
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10-28
Sublevels
Energy levels are subdivided
into sublevels.
n = 1 has the sublevel 1s.
n = 2 has the sublevels 2s
and 2p.
Each sublevel is made up of
orbitals of the same type
and energy.
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10-29
Electron Spin
Each electron in an atom appears to be spinning
on its axis.
Pauli exclusion principle states that an atomic
orbital can hold a maximum of two electrons,
which must have opposite spin.
What is the maximum number of electrons in
any orbital?
2
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10-30
Electron Spin
Pauli Exclusion Principle
• No two electrons in an atom can be the same
in all ways.
• There are four ways that electrons can be the
same:
 Electrons can be in the same principal energy
level.
 They can be in the same sublevel.
 They can be in the same orbital.
 They can have the same spin.
Some Allowed
Waveforms
s Sublevels
• Every principal energy level has
an s sublevel that contains a
single s orbital. (1s, 2s, 3s, etc.)
• There is a 90% probability of
finding the electron within a
spherical region surrounding
the nucleus.
• Each s orbital holds 2 electrons
with opposite spin.
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p Sublevels
• Every principal energy level starting at n = 2 has a
p sublevel (2p, 3p, etc.) that contains 3 equal
energy p orbitals. The orbitals only differ by their
orientation in 3-D space.
Copyright 2012 John Wiley & Sons, Inc
10-35
Your Turn!
• What is the maximum number of electrons in
a 2p orbital?
A 2p sublevel holds 6 electrons, 2
a. 2
electrons per orbital.
b. 4
c. 6
d. 8
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d Sublevels
• Every principal energy level starting at n = 3
has a d sublevel (3d, 4d, etc.) that contains 5
equal energy d orbitals. These orbitals have
more complex shapes and are higher in
energy than the s and p orbitals.
Copyright 2012 John Wiley & Sons, Inc
10-37
Your Turn!
• What is the maximum number of electrons in
a 3d sublevel?
A 3d sublevel has 5 orbitals, so it holds
a. 2
10 electrons, 2 electrons per orbital.
b. 4
c. 6
d. 10
Copyright 2012 John Wiley & Sons, Inc
10-38
Objectives for Today



Historical models of the atom
Electromagnetic radiation & the atom
Electron configurations
10-39
Objectives for Today


Atomic configurations
The Periodic Table
40
Principal Energy Levels
Principal Energy levels
• are assigned numbers n = 1,
2, 3, 4, and so on.
• increase in energy as the
value of n increases.
• are like the rungs of a ladder
with the lower energy levels
nearer the nucleus.
41
Summary of Electronic Configurations
Principal Energy Levels (n) have a maximum number of
electrons equal to 2n2.
Principal Energy level
n=1
n=2
n=3
Maximum number of electrons
2(1)2 = 2(1) = 2
2(2)2 = 2(4) = 8
2(3)2 = 2(9) = 18
The number of subshells is the same as n
42
Summary of Electronic Configurations
• Each subshell is composed of orbitals
• The number of orbitals depends on the
subshell
• Maximum of 2 electrons per orbital
Subshell
Number of Orbitals
Electrons
s
1
2
p
3
6
Copyright 2012 John Wiley & Sons, Inc
d
5
10
f
7
14
10-43
Orbitals
An orbital
• is a three-dimensional space around a nucleus, where
an electron is most likely to be found.
• has a shape that represents electron density (not a
path the electron follows).
• can hold up to 2 electrons.
44
Orbitals
An s orbital
•has a spherical shape around the nucleus.
•is found in each energy level.
A p orbital
• has a two-lobed shape.
• is one of three p orbitals in each energy level from n = 2.
Three p orbitals make up a p subshell
45
Orbitals
46
Electron Level Arrangement
In the electron level arrangement for the first 18
elements
• electrons are placed in energy levels (1, 2, 3, etc.),
beginning with the lowest energy level
• there is a maximum number in each energy level.
Energy level
Number of electrons
1
2 (up to He)
2
8 (up to Ne)
3
8 (up to Ar)
4
2 (up to Ca)
47
Rules for Distributing Electrons
1. No more than two electrons can occupy one
orbital.
2. Electrons occupy the lowest energy orbitals
available. s < p < d < f for a given value of n
3. Each orbital in a sublevel is occupied by a
single electron before a second electron
enters. (Hunds Rule)
Copyright 2012 John Wiley & Sons, Inc
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Your Turn!
• In the fourth principal energy level (n = 4),
which sublevel contains electrons with the
greatest energy?
a. 4s
b. 4p
c. 4d
d. 4f
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10-49
Your Turn!
• How many orbitals are found in a 5p sublevel?
a. 1
b. 3
c. 5
d. 7
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10-50
Your Turn!
• What is the maximum number of electrons
that can occupy the third principal energy
level (n = 3)?
a. 2
b. 6
c. 8
d. 18
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10-51
An atom consists
• of a nucleus that
contains protons
and neutrons.
• of electrons in a
large, empty space
around the
nucleus.
Copyright © 2009 by Pearson Education, Inc.
52
Different Expressions of Atomic Structure
• One way to indicate atomic structure shows
the structure of the nucleus and the number
of electrons in each energy level.
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Electron Configuration
• Another useful atomic structure shows the
distribution of electrons in the atom.
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Orbital Diagrams
• Electron configurations can also be shown
with orbital diagrams. Each box represents an
orbital.
• Up and down arrows represent electrons of
opposite spin.
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10-55
Atomic Structure
• 3Li
1s22s1
1s
1s
2s
• 5B
• 6C
•
• 7N
•
• 8O
•
1s22s2
4Be
2s
1s22s22p1
1s
2s
2p
1s
2s
2p
1s22s22p2
1s
2s
2p
1s22s22p2
1s
2s
2p
1s22s22p2
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Atomic Structure
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10-57
Atomic Structure
Remember to sum the superscripts in the electron
configuration. They should add up to the atomic number for the
element.
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Valence Electrons
• The valence electrons include all of the
electrons in the highest principal quantum
number (the outermost energy level).
• These electrons are the electrons that are
involved in bonding.
• Phosphorus: 1s2 2s2 2p6 3s2 3p3
• Phosphorus has 5 valence electrons.
Copyright 2012 John Wiley & Sons, Inc
10-59
Your Turn!
• Atoms of which element have the following
electron configuration?
•
1s2 2s2 2p6 3s23p6
a. Cl
b. Ca
c. Ar
d. S
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10-60
Periodic Table
61
Groups and Periods
Copyright © 2009 by Pearson Education, Inc.
62
Groups and Periods
On the periodic table,
• elements are arranged according to similar properties.
• groups contain elements with similar properties in vertical
columns.
• periods are horizontal rows of elements.
63
The Periodic Table
• Each horizontal row in the periodic table is
called a period.
• The number of each period corresponds to
the outermost energy level of the element.
• For example, Ar is in period 3 and its
outermost energy level is 3.
• 1s2 2s2 2p6 3s23p6
• Argon has 8 electrons in energy level 3.
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The Periodic Table
• Groups or Families contain elements whose
properties are similar.
• Representative Elements – A Groups
• Alkali Metals –1A
• Alkaline Earth Metals – 2A
• Halogens – 7A
• Noble Gases – 8A
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Other Groups to Know
• Transition Metals – B Groups
• Inner Transition Metals
– Lanthanides (Rare Earth) – Atomic Nos. 58 -71
– Actinides – Atomic Nos. 90 – 103
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Your Turn!
• Which element is a transition element?
a. sodium
b. fluorine
c. copper
d. lead
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10-67
Your Turn!
• Chlorine is a member of what family of
elements?
a. Noble gases
b. Alkali metals
c. Halogens
d. Chalcogens
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10-68
Valence Electrons and Groups
In the following groups, the group number is the number
of valence electrons.
Elements within a group have the same valence electron
configuration.
10-69
Your Turn!
• In which category of the periodic table does
each element contain valence electrons in the
second principal energy level?
a. The alkaline earth elements
b. The alkali metals
c. Group 2A
d. Period 2
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10-70
Your Turn!
• On the periodic table, elements in the same
group contain the same number of
a. Protons
b. Electrons
c. Principal energy levels in their ground state
d. Valence electrons in their ground state
Copyright 2012 John Wiley & Sons, Inc
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Electron Configurations
and the Periodic Table
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10-72
Electron Configurations
and the Periodic Table
1. The number of the period corresponds with the
highest occupied energy level.
2. The group numbers for the representative
elements are equal to the total number of valence
electrons.
3. The elements within a group have the same
number of valence electrons.
4. The elements within each of the s, p, d, f blocks
are filling s, p, d, f orbitals.
5. There are discrepancies within the transition
elements.
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10-73
Order of Electron Energies
Order of Electron Energies
Abbreviated Electron Configurations
Use the symbol of the nearest preceding noble
gas to represent the electron configuration of
the core electrons.
Phosphorus: 1s2 2s2 2p6 3s2 3p3
Core
Electrons
[Ne] 3s2 3p3
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Valence
Electrons
10-76
Your Turn!
• The electron configuration, [Ar] 4s1, is the
ground state electron configuration of
a. Potassium
b. Phosphorous
c. Fluorine
d. Sodium
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10-77
Your Turn!
• The electron configuration, [Ne] 3s2 3p1, is the
ground state electron configuration of
a. Sodium
b. Aluminum
c. Argon
d. Sulfur
Copyright 2012 John Wiley & Sons, Inc
10-78
Objectives for Today


Atomic configurations
The Periodic Table
79