Bohr model A model of the atom proposed by
Niels Bohr in 1913 that showed electrons in fixed
orbits around the nucleus but acting in some ways like
waves.
boiling point The temperature at which the vapor
pressure of a liquid is equal to the external atmospheric
pressure. A normal boiling point is considered to be the
boiling point at normal atmospheric pressure (101.325
kPa).
boiling-point elevation The increase in the boiling
point of a liquid due to the presence of a solute. The
extent of the increase is based on concentration and
molecular weight.
Boltzmann distribution A formula for calculating
the populations of different energy states at a given
temperature. Higher energy quantum levels have a
lower probability of being occupied.bomb calorimeter A rigid device used to measure
the heat transfer (released or absorbed) during a chemi-
cal reaction under conditions of constant volume.bond There is a chemical bond between two atoms
or groups of atoms when the forces acting between
them are such as to lead to the formation of an aggre-
gate with sufficient stability to make it convenient for
the chemist to consider it as an independent “molecular
species.” In the context of this encyclopedia, the term
refers usually to the COVALENT BOND.
See also AGOSTIC; COORDINATION; HYDROGEN
BOND; MULTICENTER BOND.bond dissociation SeeHETEROLYSIS; HOMOLYSIS.bond-dissociation energy The energy required to
break a given BONDin a compound. For example: CH 4
→H 3 C + H, symbolized as D(CH 3 –H).
See also BOND ENERGY; HETEROLYTIC BOND-
DISSOCIATION ENERGY.bond energy Atoms in a molecule are held together
by covalent bonds, and to break these bonds, atoms
need bond energy. The source of energy to break thebond energy 31Boiling point. When a substance changes from liquid to gas at a
fixed temperature
Bond + double covalent bond in oxygen. A bond is what holds
atoms together in a molecule.