Chemistry Reference
In-Depth Information
5.
[MgO]—Magnesium, an alkaline earth metal with two valence electrons,
has an oxidation number of +2. Oxygen, a nonmetal with six valence
electrons, has an oxidation number of -2. They combine in a 1:1 ratio
because +2 + -2 = 0.
6.
[K
2
S]—Potassium is an alkali metal with an oxidation number of +1. Sulfur,
a nonmetal with six valence electrons, has an oxidation number of -2. They
combine in a 2:1 ratio because 2(+1) + (-2) = 0.
7.
[(NH
4
)
2
SO
4
]—Ammonium (NH
4
+
) is a polyatomic ion with a charge of +1.
Sulfate (SO
4
2-
) is a polyatomic ion with a charge of -2. These ions combine
in a 2:1 ratio because 2(+1) + (-2) = 0. Because we need two of the
ammonium ions, we must enclose the polyatomic ion in parentheses and put
a subscript of 2 on the outside.
8.
[Ba(OH)
2
]—Barium is an alkaline earth metal with two valence electrons
and an oxidation number of +2. The hydroxide ion (OH
-
) has an oxidation
number of -1, so the two ions combine in a ratio of 1:2 because
(+2) + 2(-1) = 0.
Lesson 5-3 Review
1.
[lithium carbonate]—Carbonate (CO
3
2-
) is a polyatomic ion, and we never
change the name of polyatomic ions. Lithium is the positive ion, and we
never change the name of the positive ion. Adding the names of the ions
together gives us our answer.
2.
[calcium bromide]—Calcium is the positive ion, and we don't change its
name. Br is bromine, but we change the ending of its name to “ide” when it
forms a negative monatomic ion.
3.
[strontium sulfide]—Sr is the elemental symbol for strontium, our cation. S
is the elemental symbol for sulfur. We change the ending of the names of
monatomic negative ions to “ide,” hence our answer.
4.
[copper (I) oxide]—Copper is one of the elements with multiple oxidation
states, so we must indicate the oxidation number of copper in the name of
the compound. Because copper combines with oxygen in a 2:1 ratio in
Cu
2
O, and the oxidation number of oxygen is -2, the oxidation number of
copper must be +1 because 2(+1) + (-2) = 0.
5.
[nitrogen (IV) oxide]—Nitrogen shows more than one possible oxidation
number, so we must indicate the oxidation number of nitrogen in our
formula name. Oxygen has an oxidation number of -2, and there are 2
atoms of oxygen balancing out one atom of nitrogen in the formula NO
2
.
Therefore, nitrogen must be showing an oxidation state of +4. Remember:
(+4) + 2(-2) = 0.
