 Did you ever wonder why some things are liquid at room temperature while other things are solids or gases? The state of matter, solid liquid gas, is determined by the type of molecule and how those molecules are attracted to one another. So in this section, what we're going to look at is the geometries of the compounds. And then we're going to look at the difference in their physical properties. For example, this is a model of a diamond. And you can see that these carbon atoms, not only are they attracted by covalent bonds from atom to atom, but they're attached to near neighbors. And so you can see the way these are together makes it very strong. Graphite is made of the same material as diamond. The carbons are attached to carbons, but look at the links between this carbon bond and this carbon bond. So when you write with a pencil, Ed, you're actually breaking this bond right here and leaving behind a few layers of graphite. We're going to classify compounds by what forces hold them together. For example, ionic or covalent. And then we're going to determine the type of intermolecular forces. And then from those intermolecular forces, we're going to be able to predict some physical properties like melting point, boiling point, volatility, conductivity, and solubility.