“What exactly keeps groups molecules together?”
Have you ever wondered why even through objects are made of molecules moving around in space, they seem to be able to keep their form? Well, let’s think about it. First of all, let’s view everything from a microscopic standpoint. When molecules are close to one another, they have a tendency to form associations with one another resulting from a phenomena called intermolecular forces. The forces (in increasing order of strength) include london dispersion (in which all molecules experience), dipole-dipole interaction (when two or more electrically charged molecules come in close proximity within one another), and hydrogen bonding (when a hydrogen atom of one molecule comes into close proximity of an oxygen[O], nitrogen[N], or fluorine[F] of another). What I find personally amazing is how billions of these forces over time will manifest into the everyday material objects that we experience everyday!