Textbook 2A.23

[Chelsea Greene 1L]

I was wondering how to go about starting these problems:
On the basis of the expected charges on the monatomic ions, give the chemical formula of each of the following compounds:
a) magnesium arsenide
b) indium (III) sulfide ---- what does the (III) mean in this problem?
c) aluminum hydride
d) hydrogen telluride
e) bismuth (III) fluoride

[Sophie Vikram 1L]

I would assume that these problems are just nomenclature. You are going from the name to the formula so, magnesium arsenide would be:

Mg2+ As+/- 3
we need charges to be neutral so we will have 3Mg2+ and 2As3- to have +6/-6

So our formula will be Mg3As2

I would recommend looking at Nomenclature Fundamentals in the book if you get confused with suffixes and prefixes.

A general rule of thumb is that the suffix -ide means that a nonmetal is forming an anion

The (III) refers to the charge of the transition metal because the transition metals often depend on their anion to determine charge. indium (III) refers to Indium3+