Sometimes, electrons will feel most comfortable when they are orbiting two nuclei, so the nuclei effectively share their charges in a covalent bond. This is how atoms of hydrogen and oxygen combine to form water molecules. But the molecule they form is lopsided, with two smallish hydrogen atoms glomming on to one side of a larger oxygen atom. That odd shape distributes negative and positive charges unevenly over the molecule’s surface and confuses hydrogen atoms, which often get attracted to the oxygen atoms in neighboring molecules. That attraction explains why water molecules can stick
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