activity.
pi bond A bond between p orbitals.
pile A general term for a nuclear reactor; specifically, a graphite-moderated
reactor in which uranium fuel is distributed throughout a “pile” of graphite
blocks.
pitchblende A massive variety of uraninite that contains a small amount of
radium.
plasma Very hot ionized gases.
polar covalent bond A bond in which electrons are closer to one atom than to
another. See also polar molecule.
polar dot structure Representation of the arrangements of electrons around the
atoms of a molecule in which the polar characteristics are shown by placing the
electrons closer to the more electronegative atom.
polar molecule A molecule that has differently charged areas because of unequal
sharing of electrons.
polyatomic ion A group of chemically united atoms that react as a unit and have
an electric charge.
polymerization The process of combining several molecules to form one large
molecule (polymer). (a) Additional polymerization: The addition of
unsaturated molecules to each other. (b) Condensation polymerization: The
reaction of two molecules by loss of a molecule of water.
positron A positively charged particle of electricity with about the same weight
as the electron.
potential energy Energy due to the position of a body or to the configuration of
its particles.
precipitate An insoluble compound formed in the chemical reaction between two
or more substances in solution.
proteins Large, complex organic molecules, with nitrogen an essential part, found
in plants and animals.
proton A subatomic particle found in the nucleus that has a positive charge.
qualitative analysis A term applied to the methods and procedures used to
determine any or all of the constituent parts of a substance.
quantitative analysis A term applied to the methods and procedures used to
determine the definite quantity or percentage of any or all of the constituent
parts of a substance.
quenching Cooling a hot piece of metal rapidly, as in water or oil.
radiation The emission of particles and rays from a radioactive source; usually
alpha and beta particles and gamma rays.