http://www.ck12.org Chapter 27. Glossary
27.18 R
radiation
The emission of energy through space in the form of particles and/or waves.
radioactive dating
A process by which the approximate age of an object is determined through the use of certain radioactive
nuclides.
radioactive decay
A reaction in which a nucleus spontaneously disintegrates into a slightly lighter nucleus, accompanied by the
emission of particles, energy, or both.
radioactive tracer
Radioactive atoms that are incorporated into substances so that the movement of these substances can be
tracked by a radiation detector.
radioactivity
The spontaneous breakdown of an atom’s nucleus by emission of particles and/or radiation.
radioisotope
An isotope of an element that is unstable and undergoes radioactive decay.
rate-determining step
The slowest step in the sequence of steps in a reaction mechanism.
rate law
An expression showing the relationship of the reaction rate to the concentrations of each reactant.
reactant
Substance that is present at the start of a chemical reaction.
reaction mechanism
The sequence of elementary steps that together comprise an entire chemical reaction.
reaction rate
The change in concentration of a reactant or product with time.
real gas
A gas that does not behave according to the assumptions of the kinetic-molecular theory.
recrystallization
The process of dissolved solute returning to the solid state.
redox reaction
Another term for an oxidation-reduction reaction—a reaction that involves a transfer of electrons.
reducing agent
A substance that causes reduction by losing electrons.
reduction
The full or partial gain of electrons or the loss of oxygen.
reduction potential
A measure of the tendency of a given half-reaction to occur as a reduction in an electrochemical cell.
rem
The amount of ionizing radiation that does as much damage to human tissue as is done by 1 roentgen of
high-voltage x-rays.
representative element
Ans-block element.
representative particle
The smallest unit in which a substance naturally exists, usually an atom, ion, molecule, or formula unit.
resonance