Allotropes
Some elements exist in different forms in the same physical state. The chemical properties are same but the physical properties are different. The best example is carbon. There are two allotropes; diamond and graphite. Diamond is hard and colourless, graphite is flakey and black. Other elements which exist in different allotropic forms are sulphur, phosphorus and tin.

Allotropy
The ability of certain elements to exist in more than one physical form. Carbon, sulphur, and phosphorus are the most common examples. Allotropy is more common in groups 14, 15 and 16 of the periodic table than in other groups.

Alnico (trademark)
The term used for any of a group of very hard brittle alloys which are used to make powerful permanent magnets of high coercive force. They
have nickel, aluminium, cobalt, and copper in various proportions. Iron, titanium, and niobium can also be present.

Alpha decay
A radioactive transformation in which an alpha particle is emitted by a nuclide.

Alpha emission
Ejection of alpha particles from the atomic nucleus.