Solid, liquid and gas are the most common states of matter on Earth. Solid is the state in which matter maintains a fixed volume and shape as intermolecular attractions keep the molecules in fixed spatial relationships. Liquid is the state in which matter maintains a fixed volume but adapts to the shape of its container as intermolecular attractions keep molecules in proximity, but do not keep the molecules in fixed relationships. Gas is the state in which matter expands to occupy whatever volume is available as molecules are comparatively separated and intermolecular attractions have relatively little effect on their respective motions.
Plasma is a highly ionized state that occurs at high temperatures. The intermolecular forces created by ionic attractions and repulsions result in distinct properties of plasma, described as a fourth state of matter.
van der Waals forces are the intermolecular forces that cause molecules to cohere in liquid and solid states of matter, and are responsible for surface tension and capillary action.
The gas laws are predicted by the kinetic theory which relates temperature to average kinetic energy. Kinetic theory explains the pressure‐volume law (Boyle's law), pressure‐temperature law (Gay–Lussac's law), temperature–volume law (Charles' law), Dalton's law of partial pressures and Graham's law of effusion. Van der Waals equation of state for a real gas corrects for deviation from ideal behavior.
Crystalline solids have highly ordered arrangement of particles within them, which can be described in terms of repeating three dimensional arrays of points called lattices. Amorphous solids lack the internal structure of crystalline solids. Information about crystalline structures is obtained from X‐ray diffraction patterns.
Crystals can be divided into four different types: ionic, molecular, covalent and metallic. Their properties depend on the kinds of particles within the lattice and on the attractions between the particles.