Examples

Examples

a. CuO
b. CaCl₂
c. Iron(III) sulfate
d. Aluminum sulfide

Solutions

a. Copper(II) oxide

This is the correct name because copper is a
transition metal, which means it requires a Roman
Numeral (for identification of its charge).
We know it is two(II) because there is one copper atom
to every oxygen atom, and oxygen's most common charge is -2.
The ending on oxygen changes to ide because it has gained two
electrons(e-), becoming an anion.

b. Calcium chloride

This is the correct name because calcium is a
representative element and does not require a
Roman Numeral (the charge is known by locating
calcium in the IIA column). The chlorine name
becomes chloride as it gained an e-, becoming an anion.

c. Fe₂(SO₄)₃

This is the correct formula because the symbol for
for Iron is Fe and the symbols for sulfate
(a polyatomic ion) is SO₄. The subscripts on each
species is a result of the necessary ration to
achieve a neutral compound. Since Fe has a +3 charge
communicated by the Roman Numeral III, and the sulfate
is a polyatomic ion with a charge of -2, the two
species must be placed in a ratio of two irons (Fe)
to three sulfates (SO₄).

d. Al₂S₃

This is the correct formula because the symbol for
Aluminum is Al and the symbol for sulfide is S,
(this is the anion of sulfur the element). The subscripts
are explained because the most common charge for Al is +3
and the most common charge for S is -2. The ratio of two Al
to three S is the lowest ratio that yields a neutral compound.