Glossary: General Chemistry

1. colloid: after kolla, the Greek word for glue, following the terminology of Thomas Graham.

2. covalent bonds: Most polymers contain atoms held in a molecular structure by covalent bonds. These bonds are formed through the sharing of electrons, electrically charged particles within an atom. Sharing electrons reduces the energy level of the individual atoms. These bonds are maintained until other chemical reactions encourage atom combinations which yield lower energies.

3. hydrogen bond: a very strong attractive force between a hydrogen atom of one molecule and an atom of either nitrogen, oxygen, or fluorine of another molecule. The hydrogen atom is generally bonded to a nitrogen, oxygen, or fluorine atom.

4. hydrophilic and hydrophobic: liking or disliking water and, therefore, soluble or not soluble in water, respectively. Hydrophilic interactions are complicated and controversial. However, naively we know that water consists of dipolar molecules, and we therefore expect that charged or polar molecules can gain some polarization energy in water. On the other had, organic molecules with low polarizability and no dipoles will disrupt the preferred structure of nearby water molecules and increase their engergy. Oils, therefore, separate from water and will not dissolve.

5. molecular weight (molar mass): the total weight of all the atoms in a molecule. The weight of each atom is simply its total number of protons and neutrons in the atom. Thus, the molecular weight of a molecule is the total number of protons and neutrons in all the atoms in that molecule. Obviously, the more atoms there are in a molecule, the higher its molecular weight will be. A water molecule has a molecular weight of 18. A sugar (sucrose) molecule has a molecular weight of 342. Macromolecules have molecular weights in the thousands or even millions. A good sample of nylon normally has an average molecular weight of around 18,000.

6. molecule: group of atoms bound together by covalent bonds.