Chemistry Reference
In-Depth Information
the spin quantum number, indicates the spin of the
electron on its axis. The limits on the quantum numbers
(Table 4.1) must be memorized. The Pauli exclusion prin-
ciple states that no two electrons in an atom can have the
same set of four quantum numbers. (Section 4.3)
The rule governs the order of increasing en-
ergy of the electrons in the atom. Subshells are filled with
electrons in the order of increasing with due re-
gard for the limitations on the quantum numbers and for
the Pauli exclusion principle. In each case, the “last” elec-
tron can be added to the configuration of the element be-
fore, using a procedure known as the build-up principle.
(Section 4.4)
Electrons in a given shell of an atom all have the
same
n
value. Electrons in a given subshell of an atom all
have the same
n
value and the same value. Electrons in
a given orbital of an atom all have the same
n
value, the
same value, and the same value. By convention,
subshells are designated using lowercase letters that cor-
respond to the various values, and the electronic config-
uration of an atom is written using superscripts for the
numbers of electrons occupying the subshells (for exam-
ple, indicates that two electrons occupy the 1
s
sub-
shell). (Section 4.5)
Electrons in the various orbitals occupy portions of
space having specified shapes (see Figure 4.8). (These are
m
s
,
important when the shapes of molecules are considered in
Section 13.4.) (Section 4.6)
Energy level diagrams portray electrons' occupation
of the orbitals in an atom. Such diagrams are useful for
understanding Hund's rule and atoms' magnetic proper-
ties. Hund's rule states that in partially filled subshells,
the electrons occupy orbitals singly and have the same
spins as far as possible. If all the electrons in a substance
are paired (two electrons in each occupied orbital), the
substance will be repelled slightly from a magnetic field.
However, if at least one electron in each formula unit is
unpaired, the substance will be drawn into a magnetic
field. (Section 4.7)
The properties of the elements stem from their elec-
tronic configurations, and the properties place them in
their locations in the periodic table. In each group, the
elements have a characteristic outermost electronic config-
uration. The existence of the transition and inner transi-
tion elements stems from adding electrons to inner shells
after outer shells have been started. Because the periodic
table reflects the electronic structures of the atoms, it can
be used as a memory device when writing electronic
configurations. The ability to write and understand such
configurations is a very important skill. (Section 4.8)
n
/
n
/
,
/
/
m
/
/
1
s
2
Items for Special Attention
The frequency of light is a number per second, so its unit is
the reciprocal of seconds: 1/s or
values?” The number of
m
/
values is the number of orbitals
■
s
1
.
The units of
h
are
in the subshell.
joules
times
seconds.
We can think of electrons in shells as being similar to small
children on a ladder: They can never be between levels and
are most stable at the lowest energy level possible.
■
When electrons undergo transitions to higher shells, en-
ergy is
absorbed
by the atom; when electrons undergo
transitions to lower shells, energy is
emitted
by the atom.
■
The
p
,
d
, and
f
orbitals have more than one lobe each. Do
not mistake each lobe for a separate orbital.
■
There is a difference between the questions “How many
values are possible?” and “What are the possible
m
/
■
m
/
Answers to Snapshot Reviews
(6.63
10
34
J
#
s) (3.00
10
8
m/s)
1.73
10
8
m
1
2
1
2
.
hc
l
B. or ( does not depend on the value of any
other quantum number.)
C. Seven (
m
s
4.1 A.
E
3,
2,
1, 0, 1, 2, 3
)
1.15
10
17
J
4.4 A. (a) X (lower
n
/
), (b) X (equal
n
/
,
B. (a) The energy decreases.
(b) The wavelength increases.
4.2 A. It was the first postulate of discrete energy levels in
atoms, a critical breakthrough.
B. Four. (4 £ 3 £ 2 £ 1; 4 £ 3 £ 1; 4 £ 2 £ 1;
4 £ 1)
4.3 A. Any positive integer. (The integers 1 through 7 are the
most important.)
lower
n
), and
(c) Y (lower
n
/
)
1
s
2
2
s
2
2
p
4
1
s
2
2
s
2
2
p
6
3
s
2
3
p
4
4.5 A. (a) O:
; (b) S:
1
s
2
2
s
2
2
p
6
3
s
2
3
p
6
4
s
2
3
d
5
B. Mn:
4.6 A. (a) The
y
-axis, (b) the
z
-axis, and (c) the
x
- and y-axes
4.7 A. (a) Three, (b) Two
4.8 A. [Rn] 7
s
2
6
d
1
5
f
14
