Water, of course, has a chemical formula H2O: one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom. The reason that water forms a liquid is that oxygen is relatively electronegative. Oxygen attracts electrons much more strongly than hydrogen, resulting in a net positive charge on the hydrogen atoms, and a net negative charge on the oxygen atom. The presence of a charge on each of these atoms gives each water molecule a net dipole moment. Electrical attraction between water molecules due to this dipole pulls individual molecules closer together, making it more difficult to separate the molecules and therefore forming a liquid at room temperatures and raising the boiling point. This attraction is known as hydrogen bonding. This bond is strong enough to create many of the peculiar properties of water, such as liquid cohesion, formation of a meniscus in a container, etc. (Wikipedia, 2010).

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