The particles move at random because they have overcome the intermolecular forces of attraction. When a gas is raised to extreme temperatures, over 5000 o C, they have so much kinetic energy that their collisions will break electrons out of the atoms, and a change in physical state occurs. Ionic compounds have strong electric charges holding the ions together and exist as solids. Nonpolar molecular compounds of low molecular mass tend to be gases. Greater molecular mass and greater polarity both tend to make substances more dense, producing either liquid or solid.
Weak forces involve the attraction of the electrons of one atom for the protons of another atom.
When these forces interact between molecules, they are known as van der Waals forces . The hydrogen electron is attracted toward the eight protons of oxygen. The shape of the water molecule causes one side of the molecule to have a slightly positive charge and the other side of the molecule to have a slightly negative charge. Water molecules are attracted to each other because of their polar characteristics. The negative side of one molecule is attracted to the positive side of another molecule.