Chemistry Reference
In-Depth Information
Practice Problem 16.8
What are three possible oxidation states of
copper?
1
Constant
1 or
0
Vary in
steps of 2
Vary in steps of 1
0 or positive
The rules given previously do not predict all of the oxidation numbers of
the elements in their compounds, and there is no certainty that the oxidation
numbers predicted by these rules will be those of the element in its most sta-
ble or most important compounds. Other oxidation states can be deduced by the
location of the element in the periodic table. In their compounds, the alkali met-
als, alkaline earth metals, and group IIIB metals have constant oxidation states.
The main group elements to the right of the transition group elements have oxi-
dation numbers that usually vary in steps of 2. The transition group elements
have oxidation numbers that may vary in steps of 1, and only a few of these
elements have oxidation numbers equal to The oxidation numbers of the
lanthanides are mostly The elements in the first half of the actinide series
have oxidation numbers that increase from to but the elements of the
last half of that series have oxidation numbers equal to
Mostly
3
3 to
6 Mostly
3
Figure 16.2
Periodic
Variation of Oxidation Number
1.
3.
3
6,
3.
These generaliza-
tions are illustrated in Figure 16.2.
EXAMPLE 16.9
What are the possible positive oxidation numbers of sulfur?
Solution
The maximum oxidation number of sulfur, equal to its group number, is
Because the oxidation numbers vary mostly in steps of 2 in this portion of the
periodic table, we can deduce (correctly) that sulfur also has and as
oxidation numbers. Examples of compounds in which sulfur has these three oxi-
dation numbers are
6.
4
2
SF
6
,
SF
4
,
and
SF
2
.
Practice Problem 16.9
What are four positive oxidation numbers of
bromine?
ENRICHMENT
M
etals with high oxidation numbers tend to
act somewhat like nonmetals. For example, many
transition metals form oxoanions, such as perman-
ganate ion, chromate ion, and dichromate ion, in
which the metal is covalently bonded to oxygen. The
ability to form covalent bonds to oxygen is evidence
of these metals' more covalent nature. (In their low ox-
idation states, most metals typically exist in ionic
compounds as monatomic cations.) Titanium(IV)
chloride is an example of a compound in which the
metal has a high oxidation number. It is a liquid at
room temperature, and the liquid does not conduct
electricity well. These characteristics are typical of co-
valent compounds. Because this is a binary covalent
compound, it may be named titanium tetrachloride,
using the prefix in Table 6.1, but modern practice
prefers the Stock system name. It is easy enough to
write the formula for the compound from either name,
and either name is acceptable.
