How many atoms are there in a molecule of H2O?

A molecule of water, or H2O, consists of two hydrogen atoms and one oxygen atom. To determine the total number of atoms in a molecule of water, you simply add the number of hydrogen atoms to the number of oxygen atoms. In this case, with two hydrogen atoms and one oxygen atom, the calculation is 2 (hydrogen) + 1 (oxygen) = 3 total atoms.

This understanding is foundational in chemistry, especially when studying the composition of compounds. The molecular formula H2O explicitly indicates that for every molecule of water, there are two hydrogen atoms bonded to one oxygen atom, illustrating the essential ratios that define water's structure.