Why Is Milk White?: & 200 Other Curious Chemistry Questions (2013)
8. Chemistry in the World
What does water have to do with chemistry?
Most of chemistry deals with water, and water has been called the “universal solvent.” Both of these things have to do with water’s ability to form hydrogen bonds.
These bonds are the reason sodium chloride can dissolve easily in water. In a molecule of water, the oxygen atom attracts the electrons from the hydrogens so strongly that they stay around the oxygen atom most of the time and only sometimes swing back around to the hydrogen atoms. This makes the oxygen atom slightly negative and leaves the hydrogen atoms slightly positive. The positive hydrogen atoms on the water molecule attract the negative chloride ions in the salt. The negative oxygen atom in the water molecule attracts the positive sodium ion in the salt. This attraction competes with the attraction of the sodium and chlorine for each other and has the effect of weakening their attraction. If there is enough heat energy to jostle the atoms around, the salt will dissolve in the water.
More generally, a hydrogen bond is the attraction of the positive hydrogen nucleus to negative ions or negative parts of other molecules. Hydrogen bonds also make the water molecules attract one another, so water is a liquid at room temperature. Without hydrogen bonds, it would be a gas, like it is when it is hot enough that the motion of the molecules overcomes the hydrogen bonds.
Hydrogen bonds are what make ice take up more room than liquid water, so ice floats. When water freezes, hydrogen bonds lock the molecules into place, and the shape of the water molecule forces them into hexagons that take up more room than the randomly moving water molecules in liquid water. Hydrogen bonds are also very important in shaping proteins in living things, and water affects how the proteins work.