- Oxygen is one of the most electronegative elements on the periodic table. Electronegativity is the ability to attract electrons to the element. When hydrogen bonds with oxygen, hydrogen's lone electron is given to oxygen. This make the hydrogen positively charged, since it has no electron, and oxygen negatively charged since it has more electrons. These charges are greater in water because of oxygen's higher electronegativity.
- The water molecule is polar, with the oxygen end of the molecule negative and the hydrogen atoms both positive. It is this polarity that helps water molecules stick together. When two water molecules come together, the oxygen atom of one molecule is attracted to the hydrogen atoms of the other molecule. One water molecule can form four hydrogen bonds with other water molecules. The bonds that are formed are only 1/10 as strong as a covalent bond, however, the bonds are strong enough that it takes more energy to break the hydrogen bonds compared to other intermolecular forces.
- Water has a boiling point of 100 degrees Celsius. This temperature is much higher than other hydrogen bonding elements such as HCl, which boils at -80 degrees Celsius. HCl does not form strong hydrogen bonds like water does. The energy, or heat, that is required to make water boil is higher because the hydrogen bonds must be broken to change into water vapor. This is very important to all life on Earth. If water had a lower boiling point, there would be little to no liquid water on the planet.
- Hydrogen bonds are strong, but not as strong as covalent or ionic bonds between elements. This allows the bonds to break and reform repeatedly. The breaking and reformation of bonds is exactly what happens when water dissolves a substance. For example, NaCl, table salt, dissolves in water. Sodium, Na, and chlorine, Cl, are separated from another by the water. Sodium, which is slightly positive, is surrounded by the oxygen atoms of water and the chlorine atoms, which are negative, are surrounded by the hydrogen atoms present in the water molecules. This separation and surrounding of the Na and Cl atoms results in the molecule dissolving in water. Any molecule that is polar can be dissolved by water.
- Ice floats on liquid water. Water is one of the few molecules where this occurs. The reason for this is because of the hydrogen bonds. Liquid water is very dense. This is a result of the hydrogen bonds pulling water molecules together. When ice forms, the structures bonds are held in place in a lattice structure. This structure has large holes in it. The molecules are more widely spaced in ice, making it less dense than liquid water. This reduction in density is the reason why ice floats in liquid water.