Most bonds are made when a positive atom or molecule (one that is missing an electron in its outer shell) accepts an electron from a negative atom or molecule. Hydrogen is a positive ion because it only has one electron in its outer shell instead of a pair. Oxygen has paired electrons, but because it is highly electronegative one of the outer electrons is held closer to the nucleus, creating a partial negative charge. This partial negative charge attracts the electron in the outer shell of hydrogen and creates a bond. This type of bond accounts for the high surface tension in water.