matter
In some ways, a collection of gas molecules represents the simplest form of matter. Because the individual molecules are so far apart, they have only fleeting interactions with one another. In contrast, molecules that have clustered together to form a liquid or solid are constantly exerting forces on each other. In fact, it is only because of these attractive forces that molecular solids and liquids exist at all. In this lesson, we will look at some of the ways in which molecules and ions attract one another to form solids and liquids.