Summary

The Condensed States of Matter

Substances are liquids or solids if the attractive forces between ttheir particles are strong enough to overcome their motion (their kinetic energy). These forces are, in order of increasing strength, dispersion forces (London forces), dipole-dipole interaction, and hydrogen bonds. In addition to these forces, the particles in solids may be bonded to one another by ionic bonds, network covalent bonds, or metallic bonds.

A liquid has a vapor pressure that increases with temperature. When the vapor pressure of a liquid equals atmospheric pressure, the liquid boils. When the pressure of the atmosphere is 1 atm, the temperature at which a liquid boils is its normal boiling point.

Vapor pressure in the solid state is less than that in the liquid state. When the vapor pressures are equal the solid melts. Within a solid, the particles are joined by rigid bonds that define the crystal lattice of the solid.

Each substance has a specific heat for each physical state in which it occurs. Specific heat measures the rate of change of kinetic energy within the sample. Each substance also has a heat of fusion and a heat of vaporization that measure the strength of the attractive forces between the particles. The energy necessary to cause a change in temperature and/or a change in state can be calculated.