Energy radiated or transmitted as rays, waves, in the form of particles (e.g. light).

The branch of chemistry that studies the chemical changes resulting from the absorption of high-energy, ionizing radiation,  e.g. alpha particles, electrons, gamma ray, protons etc.

An atom, molecule, or ion with unpaired electrons that is likely to take part in chemical reactions.

The property possessed by some elements, e.g. uranium, of spontaneously emitting radiation (usually alpha or beta rays and sometimes also gamma rays) by the disintegration of the nuclei of atoms. Radioactivity was first discovered in 1896 by the French scientist Henri Becquerel, when he was working on phosphorescent materials.

A bow-shaped display in the sky of the colours of the visible light spectrum, caused by the refraction and reflection of the sun's rays through rain or mist.

A thin line or narrow beam of light or other radiant energy.

Substances initially present in a chemical reaction that are consumed during the reaction to make products.

Field within Physical Chemistry studying why chemical reactions occur, how to predict their behavior, and how to control them. Reaction Dynamics is mainly concerned with individual chemical events on atomic length scales and over very brief time periods.

The sequence of steps during which a chemical reaction occurs. A mechanism describes in detail what exactly takes place at each stage of a chemical transformation.

The environment where the reaction is taking place. It may be liquid, solid, heterogeneous etc.

A substance used in a chemical reaction to detect, measure, examine, or produce other substances. 

The change in direction of a wave, such as a light or sound wave, away from a boundary the wave encounters. Reflected waves remain in their original medium rather than entering the medium they encounter.

Rickets, also called osteomalacia, is an abnormal bone formation in children primarly resulting from inadequate calcium in their bones.

Abbreviation that stands for RiboNucleic Acid. One of the two main types of nucleic acid (the other being DNA), which functions in protein synthesis in all living cells. RNA is mainly involved in translating into proteins the genetic information that is carried in DeoxyriboNucleic Acid (i.e. the DNA).