C 2 H 5 OH ethanol Elements that can exist by themselves as a single atom are called monoatomic elements.
Some elements exist as two atoms on their own.
They exist as molecular compounds and are called diatomic elements. There are two elements, sulfur and phosphorus, that are called polyatomic elements because they exist as molecular compounds made up of more than two atoms. The formula for water is written after the formula for the ionic compound with a number coeffecient indicating the number present. Usually there is a point separating the ionic compound formula and the formula for water. ZnCl 2 .