Name       : Calcium 
Symbol     : Ca
Atomic #   : 20
Atom weight: 40.08
Melting P. : 839
Boiling P. : 1484
Oxidation  : +2
Pronounced : KAL-si-em
From       : Latin calx, ancient name for lime
Identified : Sir Humphry Davy in 1807; Most compounds known in ancients
Appearance : Fairly hard, silvery-white metal
Note       : About 2% of human body is composed of calcium

[Properties]

  Calcium is the most familiar member of Group IIA elements, or alkaline-
earth metals. Prior to 1800s, chemists did not regard these elements -
magnesium (Mg) and calcium, for instance - as metals. The elements form
hydroxides quite readily, so they were classified as alkaline substances.
Furthermore, they were derived from common ores taken form the earth;
therefore, it seemed proper to refer to them as earth elements. We now
know that the Group-IIA elemetns are metals, but the older nomenclature
remains.
  Calcium has a lustrous, slightly grayish appearance when it is first
cut. Surfaces exposed to the air tarnish to show a duller finish. The
metal is a good conductor of electricity, although there is no practical
application for this property.
  Like the other metals on the left-hand side of the periodic table, 
calcium is a very active metal. It combines slowly with dry air to produce
a protective coating of an oxide and a nitride. This accounts for the
tarnish that soon dulls an otherwise shiny surface on the metal. The
compounds in this instance are quite effective at preventing further
corrosion of the metal.
  Calcium metal does not combine with water explosively as do many of
highly reactive metals, but it does bubble off hydrogen gas and produce 
calcium hydroxide.