The strength and specificity of interactions between biological molecules depend on the medium in which they reside. The major biological solvent is water, although fat deposits readily dissolve hydrophobic molecules such as some pesticides and various drugs. Because of the large electronegativity of oxygen relative to hydrogen, the oxygen atom attracts electrons from the two hydrogen atoms, making them more negative and leaving the hydrogen atoms with a net positive charge. Thus, water molecules are highly polarized, and they associate with one another through hydrogen bonds. The angle between the two O—H bonds in water is not 180Degree; hence the molecule is bent, and hydrogen bonds form in which each water molecule interacts with several neighbors in a three-dimensional network. Without these interactions, water with a molecular weight of 18 would be a gas at normal atmospheric temperatures and pressures, like dinitrogen of molecular weight 28.