The important properties of ordinary water can be understood as different manifestations of one fact. Each water molecule is electrically unsymmetrical, or polar: it has a positive end and a negative end. This is because the oxygen atom exerts a stronger pull than the hydrogen atoms on the electrons they share, and because the hydrogen atoms project from one side of the oxygen to form a kind of V shape: so there’s an oxygen end and a hydrogen end to the water molecule, and the oxygen end is more negative than the hydrogen end. This polarity means that the negative oxygen on one water molecule feels an electrical attraction to the positive hydrogens on other water molecules. When this attraction brings the two molecules closer to each other and holds them there, it’s called a hydrogen bond. The molecules in ice and liquid water are participating in from one to four hydrogen bonds at any given moment. However, the motion of the molecules in the liquid is forceful enough to overcome the strength of hydrogen bonds and break them: so the hydrogen bonds in liquid water are fleeting, and are constantly being formed and broken.