Chemistry Reference
In-Depth Information
Table 13.2
Electron Affinities of Some Elements (kilojoules per mole)
H
72.6
K
48.2
Te
189.8
He
21
Ca
156
I
294.8
Li
59.7
Cr
64
Xe
40
Be
240
Ni
111
Cs
45.5
B
23
Cu
122.9
Ba
52
C
122.3
Ga
36
Ta
80
N
0.0
Ge
116
W
50
O
141.1
As
77
Re
14
F
321.5
Se
194.5
Pt
204.9
Ne
29
Br
323.9
Au
222.4
Na
52.8
Kr
39
Tl
50
Mg
230
Rb
46.8
Pb
101
Al
44
Sr
168
Bi
101
Si
119
Mo
96
Po
173
P
74
Ag
125.5
At
270
S
200.0
In
34
Rn
40
Cl
348
Sn
120
Fr
43.9
Ar
35
Sb
101
If we combine the ionization energy of sodium with the electron affinity of
chlorine, we deduce that an overall energy input is required for the reaction
Cl(g) £ Na
(g)
Cl
(g)
Na(g)
because 496 kJ is
required
to remove the electrons from a mole of gaseous
sodium atoms and only 348 kJ is
produced
when these electrons are added
to a mole of gaseous chlorine atoms. This conclusion emphasizes that we
are talking about
gaseous
atoms and ions. (When the energy to form a solid
lattice of NaCl from the ions, and other factors, are taken into account [Chap-
ter 14], the process of combining metallic sodium and gaseous chlorine mol-
ecules produces energy.)
Snapshot Review
❒
Ionization energy and electron affinity both refer to the energetics of
reaction of atoms and ions
in the gas phase.
❒
Ionization energy increases toward the right and toward the top of the
periodic table.
ChemSkill Builder 11.2
A. Arrange each of the following sets in order of increasing ionization
energy: (a) Sr
Mg
Ca, (b) As
F
S, and (c) Sb
S
Se
13.3
Electronegativity and Bond Polarity
Electronegativity
(Section 5.1) is a semiquantitative measure of the electron-
attracting ability of an atom. The larger the electronegativity, the greater is the
pull on the electrons. In general, electronegativity increases to the right and
