Chemistry - A Molecular Science

is a +1 in Cl-F and Cl

O. The electrons in molecules and ions are usually paired, so 2

chlorine typically loses an odd number of electrons to attain oxidation states of +1, +3, +5, and +7 as it does in the ions ClO

1-, ClO

1- 2

, ClO

1- 3

, and ClO

1- 4

. The oxidation states of all of

the elements of Group 7A range from -1 to +7. Similarly, the oxidation states of Group 6A elements can vary from -2 to +6 and those of Group 5A from -3 to +5.

Neither atom in a bond between identical el

ements is more electronegative, so the

bonding electrons cannot be assigned to one element. Instead, half of the electrons in each bond are assigned to each atom in the bond. The result is that

the oxidation states of the

atoms in an element are all zero

. Thus, chlorine has an oxidation state of zero in Cl
. 2

The following guidelines are useful in predicting common oxidation states:

(^) •
The main group metals most often are in their
highest oxidation state (group number). This is
true because the valence electrons of main group metals are high in energy (metals have low ionization energies) and are readily transferred
to nonmetals. The exceptions are the late
metals: Sn, Tl, Pb, and Bi, which can lose only their p subshells or their entire valence shells.
(^) •
The most oxidation states formed by the transition metals are +2 and +3, but the following can be found in +1 oxidation states: Cu, Ag, Hg,
and Au. Higher oxidation states can be achieved
when the metal is surrounded by oxygen. For example, V
O 2
, CrO 5
2- 4
, and MnO
1-. 4
Metals are •
rarely
assigned negative oxidation states. This is expected because their unfilled
orbital energies are quite high, which makes it unlikely that they will bond with an atom with a higher energy electron.
Many atoms have the same oxidation state in almost all of their compounds. Thus, to determine the oxidation state of an atom in a molecule or ion, you must first assign oxidation states to those atoms that tend to a
ttain the same oxidation state in all of their
compounds.
Use the following rules to determine co
mmon oxidation states. Apply them in
the order given; that is, a rule at the top of
the list takes precedence over any rule below it.
Rule 1 The oxidation state of each atom
in an elemental substance is zero.
Rule 2 Fluorine is -1. Rule 3 Group 1A metals are +1, Group 2A metals are +2, and Groups 3A (except Tl*) and
3B are +3 in their compounds.
Rule 4 Hydrogen is +1. Rule 5 Oxygen is -2. Rule 6 Halogens are -1 except when bound to a more electronegative halogen.

• Tl can also form a +1 ion by emptying only its 6p sublevel, while
  the other Group 3 elements empty their entire valence shell.
  Rule 1
  restates our earlier conclusion that the electrons in a bond between identical
  atoms must be shared and cannot be assigned to
  one element. Some examples are Li, F
  (^2)
  and P

. 4
Rule 2

states that the most electronegative element (F) is always assigned the

Chapter 4 The Ionic Bond

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