Animation showing hydrogen bonding between molecules of water. Each water molecule is colour-coded to show its polarity. Each of its two hydrogen atoms has a slight positive charge (blue), while the central oxygen atom has a slight negative charge (red). The attractive forces between these opposite charges form temporary bonds called hydrogen bonds (black lines). At the temperature of liquid water, these bonds form and break constantly due to the motion of the molecules. Each water molecule can form four hydrogen bonds, one from each hydrogen and two from its oxygen atom, as the oxygen has two lone pairs of electrons. This means that all the charges in water balance out, and there is a strong attractive force between all the molecules. This phenomenon gives water many of its unique properties, such as its high boiling point and viscosity. Compare this situation with that of the similar compounds ammonia and methane, in clips K004 4147 and K004 4144.