| Electromagnetic Radiation (or Electromagnetic Waves):
A wave that travels though space at the speed of light, consisting of an electrical field that periodically grows and dies, alternating with a magnetic field that periodically dies and grows. Electromagnetic waves carry energy and momentum, which may be imparted when it interacts with matter.
In order of increasing frequency, the electromagnetic spectrum includes radio waves, microwaves, terahertz radiation, infrared radiation, visible light, ultraviolet radiation, x-rays and gamma rays.
Electron:
A negatively-charged sub-atomic particle. It is an indivisible,elementary particle, and is usually to be found orbiting thenucleus of an atom. Electrons in an atom (which exist in the same quantity as the number of protons in the nucleus of the particular atom, so that the overall electric charge is zero) are constrained to occupy certain discrete orbital positions or “shells” around the nucleus. Interactions between the electrons of different atoms play an essential role in chemical bonding and phenomena such as electricity, magnetism and thermal conductivity. The discovery of electrons is credited to the British physicist J. J. Thomson in 1897.
Element:
A substance that cannot be reduced any further by chemical means. It is a pure chemical substance composed of atomswith the same atomic number (i.e. the same number of protonsin its nucleus). There are 92 naturally occurring elements on Earth, and all chemical matter consists of these elements (although a further 25 have been discovered as products of artificial nuclear reactions). Elements with atomic numbers 83 or higher are inherently unstable, and undergo radioactive decay. The list of elements is usually shown in the form of a Periodic Table, in order of their atomic number (see box at right, or click ther source link for a more detailed interactive Periodic Table).
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