Answer
(a) potassium bromide: KBr
(b) calcium hydride: CaH$_2$
(c) lithium nitride: Li$_3$N
(d) aluminum chloride: AlCl$_3$
Work Step by Step
(a) potassium bromide: KBr
charge on potassium ion = 1+
charge on sulfur ion = 1-
The charges must be balanced in a compound.
1 potassium ion = 1(1+) = 1+ charge
1 bromide ion = 1(1-) = 1- charge
(1+) + (1-) = 0
The charges balance out, so you need one atom of potassium for every one atom of bromine to make a compound.
(b) calcium hydride: CaH$_2$
charge on calcium ion = 2+
charge on hydride ion = 1-
The charges must be balanced in a compound.
1 calcium ion = 1(2+) = 2+ charge
2 hydride ions = 2(1-) = 2- charge
(2+) + (2-) = 0
The charges balance out, so you need one atom of calcium for every two atoms of hydrogen to make a compound.
(c) lithium nitride: Li$_3$N
charge on lithium ion = 1+
charge on nitride ion = 3-
The charges must be balanced in a compound.
3 lithium ions = 3(1+) = 3+ charge
1 nitride ion = 1(3-) = 3- charge
(3+) + (3-) = 0
The charges balance out, so you need three atoms of lithium for every one atom of nitrogen to make a compound.
(d) aluminum chloride: AlCl$_3$
charge on aluminum ion = 3+
charge on chloride ion = 1-
The charges must be balanced in a compound.
1 aluminum ion = 1(3+) = 3+ charge
3 chloride ions = 3(1-) = 3- charge
(3+) + (3-) = 0
The charges balance out, so you need one atom of aluminum for every three atoms of chlorine to make a compound.
