Barometer

An instrument that measures atmospheric pressure.

Base

A substance that yields hydroxide ions (OH^-) when dissolved in water.

Base Ionization Constant

The equilibrium constant for the base ionization.

Battery

An electrochemical cell, or a series of combined electrochemical cells, that can be used as a source of direct electric current at a constant voltage.

Beta Rays

(b) - Electrons.

Bimolecular Reaction

An elementary step that involves two molecules.

Binary Compounds

Compounds formed from just two elements.

Boiling Point

The temperature at which the vapor pressure of a liquid is equal to the external atmospheric pressure.

Bond Dissociation Energy

The enthalpy change required to break a bond in a mole of gaseous molecules.

Bond Length

The distance between the centers of two bonded atoms in a molecule.

Bond Order

The difference between the numbers of electrons in bonding molecular orbitals and antibonding molecular orbitals, divided by two.

Bonding Molecular Orbital

A molecular orbital that is of lower energy and greater stability than the atomic orbitals from which it was formed.

Born-Haber Cycle

The cycle that relates lattice energies of ionic compounds to ionization energies, electron affinities, heats of sublimation and formation, and bond dissociation energies.

Boundary Surface Diagram

Diagram of the region containing a substantial amount of the electron density (about 90 percent) in an orbital.

Boyle’s Law

The volume of a fixed amount of gas maintained at constant temperature is inversely proportional to the gas pressure.

Breeder Reactor

A nuclear reactor that produces more fissionable materials than it uses.

British Thermal Unit

(Btu) - The amount of energy required to raise 1 pound of water by 1° Fahrenheit.

Brønsted Acid

A substance capable of donating a proton.

Brønsted Base

A substance capable of accepting a proton.

Buffer Solution

A solution of a weak acid or base and its salt; both components must be present. The solution has the ability to resist changes in pH upon the addition of small amounts of either acid or base.