Video Transcript
What is the correct way to write two water molecules using chemical formulas?
A chemical formula is an expression of chemical symbols and numerical subscripts that represents the composition of one unit of a compound. One molecule of water is composed of two atoms of hydrogen and one atom of oxygen. To express this information as a chemical formula, we need to use the chemical symbols of the elements and numerical subscripts to indicate the number of atoms of each element.
The chemical symbol of hydrogen is capital H. So, in the chemical formula, we’ll write a capital H followed by a subscript two, which indicates that one molecule of water contains two atoms of hydrogen. The chemical symbol of oxygen is capital O. So, we’ll add a capital O to the chemical formula. There’s one atom of oxygen in a molecule of water, but subscript values of one are not explicitly written in chemical formulas. So, the chemical formula of one molecule of water is H2O.
But the question asks us to write a chemical formula for two water molecules. We can do this by placing a two in front of the chemical formula for one molecule of water. A number written in front of a chemical formula is called a coefficient. This value indicates the number of discrete units, in this case the number of water molecules. Therefore, the correct way to write two water molecules using chemical formulas is two H2O.
