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Chapter 1
Copyright © 2017 Pearson Education, Inc.
Solutions to Problems
1.
The atomic number
=
the number of protons.
The mass number
=
the number of protons
+
the number of neutrons.
All isotopes have the same atomic number; in the case of oxygen, it is 8. Therefore:
The isotope of oxygen with a mass number of 16 has 8 protons and 8 neutrons.
The isotope of oxygen with a mass number of 17 has 8 protons and 9 neutrons.
The isotope of oxygen with a mass number of 18 has 8 protons and 10 neutrons.
2.
The number of protons an element has never changes. The number of electrons depends on the charge on
the element.
a. 1.
11
2.
18
3.
17
b. 1.
10
2.
18
3.
18
3.
(percentage of naturally occurring
35
Cl
*
atomic mass of
35
Cl
)
+
(percentage of naturally occurring
37
Cl
*
atomic mass of
37
Cl
)
1
.7577
*
34.969
2
+
1
.2423
*
36.966
2
1
26.496
+
8.957
2
=
35.45
4.
All four atoms have 2 core electrons in their filled first shell. (Notice that because the four atoms in the
question are in the same row of the periodic table, they have the same number of core electrons.) The elec-
trons that are not in a filled shell are valence electrons.
a.
3
b.
5
c.
6
d.
7
5.
a.
Use the aufbau principle (electrons go into available orbitals with the lowest energy) and the Pauli exclusion
principle (no more than two electrons are in each atomic orbital). The relative energies of the orbitals:
1
s
6
2
s
6
2
p
6
3
s
6
3
p
6
4
s
6
3
d
6
4
p
6
5
s
6
4
d
6
5
p
Remember that each shell has one
s
atomic orbital and three degenerate
p
atomic orbitals. The third
and fourth shells also have five degenerate
d
atomic orbitals.
Cl 1
s
2
2
s
2
2
p
6
3
s
2
3
p
5
Br 1
s
2
2
s
2
2
p
6
3
s
2
3
p
6
3
d
10
4
s
2
4
p
5
I 1
s
2
2
s
2
2
p
6
3
s
2
3
p
6
3
d
10
4
s
2
4
p
6
4
d
10
5
s
2
5
p
5
b.
They each have 7 electrons in their outer shell; in each case, 2 are in an
s
orbital and 5 are in
p
orbitals.
Notice that because the 3 elements all are in the same column of the periodic table, they have the same
number of valence electrons.
6.
The atomic numbers can be found in the periodic table on the last page of the text. Notice that elements
in the same column of the periodic table have the same number of valence electrons and that their valence
electrons are in similar orbitals.
a.
carbon (atomic number
=
6; 2 core, 4 valence):
1
s
2
2
s
2
2
p
2
silicon (atomic number
=
14; 10 core, 4 valence):
1
s
2
2
s
2
2
p
6
3
s
2
3
p
2