Transition metal
Any of the elements in the B Groups of the periodic table, all of which have partially filled d
sublevels.
Triple point
The pressure and temperature at which the solid, liquid, and vapor phases of a particular substance
coexist in equilibrium. See Phase equilibrium.
Unit cell
A three-dimensional representation of the repeating units in a crystalline solid.
Unsaturated compound
A compound with double or triple bonds.
Unsaturated solution
A solution into which more solute may be dissolved.
Valence electron
An electron in the highest occupied energy level of an atom, whose tendency to be held or lost
determines the chemical properties of the atom.
Van der Waals forces
The weak forces that contribute to intermolecular bonding, including hydrogen bonding, dipole-
dipole interactions, and dispersion forces.
Vapor pressure
The pressure exerted by a vapor when it is in equilibrium with the liquid or solid phase of the same
substance; the partial pressure of the substance in the atmosphere above the liquid or solid.