What is the maximum number of hydrogen bonds that can be formed by one molecule of water?
Hydrogen bonds are an attraction between a hydrogen atom in one molecule and the lone pair on a highly electronegative atom in a different molecule. This strongly electronegative atom is typically nitrogen, oxygen, or fluorine. Hydrogen bonding is a special type of dipole–dipole interaction, as the hydrogen will have a partial positive charge and the electronegative atom with the lone pair will have a partial negative charge. The negative charge is actually quite large because the highly electronegative atom attracts a lot of electron density. This makes hydrogen bonding a very strong intermolecular force. Water is a classic example of a molecule that forms hydrogen bonds. Hydrogen bonds form between the hydrogen atom of one water molecule and the lone pair on the oxygen atom of another molecule.
In this question, we need to determine the maximum number of hydrogen bonds that can be formed by one molecule of water. So far, we’ve drawn this water molecule with one hydrogen bond. Another hydrogen bond can be formed using the other lone pair on the oxygen atom. Each hydrogen atom in the molecule can also form a hydrogen bond. So each water molecule can form a maximum of four hydrogen bonds.