2 O. Oxygen's other four valence electrons, in two pairs, are not bonded to any other atoms, thus these are referred to as unshared pairs of electrons . Oxygen shares electrons with hydrogen, but pulls just a little harder on the electrons. The electrons are just a little closer to the oxygen than the hydrogens, so this is called a polar covalent bond . This is called hydrogen bonding . Actually, hydrogen bonding can happen with other molecules besides water as we will see later.
Water is a key ingredient in all life.
Water has many unique properties due, in great part, to its hydrogen bonding. Water sticks to itself. It forms droplets. It acts like it has a film on top. Water can absorb a lot of heat without changing temperature very much.