Homework Assignment #2 Key
Chapter 5
21. (a)
(b)
(c)
(d)
(e)
(f)
16 protons
41 protons
13 protons
29 protons
26 protons
26 protons
18 neutrons
52 neutrons
14 neutrons
34 neutrons
30 neutrons
29 neutrons
15 electrons
41 electrons
13 electrons
28 electrons
24 electrons
23 electrons
73. (a)
(b)
(c)
(d)
(e)
n=1
n=4
n=3
n=3
n=4
l
l
l
l
l
=
=
=
=
=
0
0
1
2
3
83. (a)
(b)
(c)
(d)
(e)
(f)
[Ne]3s1
[Ne]3s3 3p1
[Ar]4s2
[Kr]5s2
[Xe]6s2
[Ar]4s2 3d10 4p5
n=3
n=3
n=4
n=5
n=6
n=4
89. Pauli Exclusion Principle: No two electrons in the same atom may have identical sets of 4
quantum numbers.
(a) 1s2 –
?? this does not violate the principle (PEP) (2 different ms values)
?? this would violate the PEP (same ms values)
the former arrangement is implied.
(b) 1s2 2p7 -
??
?? ?? ???
2
1s
2p7
violates the PEP (3rd p orbital has 3 electrons, 2 with the same ms value)
this also violates the Aufbau principle – (filling the 2p orbitals before
filling the 2s orbitals
(c) 1s3 -
??? violates the PEP (orbital has 3 electrons, 2 with the same ms value)
95. (a) Na:
K:
1s2 s22 2p6 3s1
1s2 s22 2p6 3s2 3p6 4s1
or
or
[Ne]3s1
[Ar]4s1
(b) They are similar in that they have the same number of outer shell electrons (1) in the
same kind of orbital (s)
(c) They are different in that they have a different number of core electrons (10 vs. 18) and
that their outer electrons are in different shells (n = 3 vs. n = 4)
97. (a)
(b)
(c)
(d)
Ti
Bi
Si
Ra
Chapter 6
27. Ionization energy – the amount of energy required to remove the outermost electron
the first ionization energy is the removal of an electron from an atom
the second ionization energy is the removal of an electron from a cation
It is generally more difficult to remove an outer electron from a cation. The nuclear charge is the
same as the atom, but the # electrons has decreased; hence, the attraction to the nucleus is
greater.
33. using the general trends that you have been taught:
least negative (least affinity)
most negative (greatest affinity)
(a) Fr
Cs
Rb
K
Na
Li
(b) At
I
Br
Cl
F
(c) Li
Be
B
C
N
O
F
(d) K
Li
C
Cl
F
in actuality (consulting Table 6.2), Cl has a greater affinity than F, hence the positions of Cl
and F should be reversed in b) and d).
41. As one moves down a group, the number of filled shells of electrons increases, which results
in greater shielding of the outermost electrons from the nucleus by the inner shells filled with
electrons, and a lower effective nuclear charge on the outermost electrons. Hence, the atom
(or ion) is larger as one moves down the group.
45. Definitions such as electronegativity, electron affinity, ionization energy, etc., are
generalized descriptions of the behavior of the elements based upon scientists’ observations.
Statement (b) is better because it reflects the fact that electronegativity is our description of
the behavior of the element, not the cause.
Chapter 7
7. There are covalent bonds (electron pair sharing) between the N and the H atoms in the
ammonium cation. The entire ammonium cation is engaged in ionic bonding with the
chloride ion.
21. two cations that are isoelectronic with Kr:
two anions that are isoelectronic with Kr:
examples of compounds they could form:
Rb+, Sr2+
Br-, Se2RbBr, SrSe, Rb 2 Se, SrBr2
47. For some substances it is possible to draw more than one Lewis structure. In this case,
neither drawing fully represents the bonding in the structure. The structure is better
approximated as an average, or resonance hybrid, of the Lewis structures.
71. In covalent compounds, the strongest forces are the covalent bonds between the atoms within
a particular molecule. The intermolecular forces between covalent molecules are relatively
weak.
In ionic compounds, the forces between atoms are the ionic bonds between the ions, which
are very strong.
Melting disrupts the intermolecular forces between molecules in covalent compounds, and
the ionic bonds between ions in ionic compounds. To overcome an ionic bond takes a lot
more energy than it takes to overcome an intermolecular force.
73. We show only partial charges on the atoms of polar molecules because no atom takes an
electron completely from the other.
Uncollected problems: Chapter 8
11. Hybridized atomic orbitals are combinations of atomic orbitals (s, p, sometimes d) on the
same atom which give the right orientations (and energies) to correctly describe the bonding
within a molecule, particularly in terms of the geometry (shape). The theory of hybrid
orbitals is useful for explaining the bonding in cases when bonding arrangements or bond
angles are significantly different than the angles between non-hybridized atomic orbitals.
19. assume that A is the central atom.
(a) AB4 –
4 ‘things’ – sp3
(b) AB2 U3 5 ‘things’ – sp3 d
(c) AB3 U 4 ‘things’ – sp3
(d) ABU4 5 ‘things’ – sp3 d
(e) ABU3 4 ‘things’ – sp3