Answer:
Covalent compounds are named by first looking at how many atoms the first element in a molecule has. We'll use H2O as an example (although it is commonly known as water). Since the H contributes two atoms to the molecule it has the prefix di-. If it had one it would be mono-, three, tri-, etc. The second element also follows that same rule, however, the ending is changed as well. In the case of oxygen, the -ygen is taken off and replaced by -ide. Therefore, the molecule H2O is also known as dihydrogen oxide.