Hydrogen bonds form between a hydrogen atom covalently bonded to an electronegative atom such as nitrogen, oxygen or fluorine and another electronegative atom with a lone pair of electrons such as nitrogen, oxygen or fluorine. In water, the electronegative oxygen atoms from two water molecules can engage in hydrogen bonding (the H of one water molecule and the O of the other). This leads to a three-dimensional network of water molecules that give it its unique properties, such as high surface tension and high specific heat capacity.