Protons and neutrons together form the nucleus of an atom while the electrons are
circling around this nucleus at a relatively great distance. Electrons are negatively
charged, protons equally but positive. The chargeless neutrons within the nucleus are
preventing the protons to repel each other like equally charged poles of a magnet
would do. The number of protons within the nucleus determines the nature of an atom
and more than a hundred different atoms are known today. These atoms (also called
elements) are depicted with a letter or a combination of letters such as C for carbon,
Cu for copper, W for tungsten and Hg for mercury. The smallest element is that of
hydrogen (H) with only one proton and one electron. The nucleus of a carbon atom
has six protons while copper has twenty-nine, tungsten seventy-four and mercury
eighty. Normally the number of electrons circling the nucleus equals the number of
protons within the nucleus, keeping the resulting charge of the atom to be zero
(remember: electrons are negatively charged, protons equal but positively).
Within solids there is interference between the outer electrons of adjacent atoms and
that binds the individual atoms together a fixed grid. At higher temperatures the
movements within the atoms increases however and the binding force keeping the
grid together decreases, causing the material to melt or vaporise. The strength of the
binding force depends on temperature and is different for each element. Copper
already melts at a temperature of 1083 degrees Celsius while pure tungsten only
melts at about 3400 degrees Celsius. Tungsten and Kanthal, an electric conductive
alloy with a high melting point, were commonly used as sources of light and infrared
radiation in incandescent (heat) lamps. Mercury is a metal that is liquid at room
temperature and it vaporises at a temperature as low as 357 degrees Celsius.
Mercury vapour was commonly used as the source of ultraviolet radiation in