The element calcium has atomic number 20 in the Periodic Table of Elements, which means it has 20 protons in its nucleus. It is group IIA. Its symbol is Ca and its atomic weight is 40.078. It is an alkaline earth metal. It was discovered by Sir Humphrey Davy in 1808. Calcium is what one-third of the weight of the human body is made of. It is also necessary for plant growth.
Calcium is the fifth most abundant element in the Earth’s crust. It is used to make cement and prepare cheese. It is also a reduction agent in the preparing of other metals. Calcium is a silvery white color. It reacts slowly with water. The reaction of calcium and water forms calcium hydroxide and hydrogen gas. It is very reactive toward the halogens (fluorine, chlorine, bromine and iodine). Calcium dissolves in even dilute hydrochloric acid.
Calcium has a density of 1.55 g/cm^3, which is the lightest of the alkaline earth metals. Although calcium has a higher electrical resistivity than aluminum or copper, it is a better conductor of electricity because of its lower density. It is a fairly large element with an atomic radius of 0.99 angstroms (an angstrom is one ten millionth of a millimeter). It is a solid at room temperature. Its melting point is 842 degrees Celsius. Its boiling point is 1484 degrees Celsius.
A good way to estimate the size of an element is the size increases from top to bottom and decreases from left to right until about three fourths of the way, where it approximately slowly increases until the last row. This last row has some of the largest elements (neon, argon, krypton and xenon), although helium and radon are small.
Calcium is essential for strong bones. It is also important for the nerves, heart and muscles to function properly. Vitamin D is important to help calcium perform properly. The principal inorganic substance in teeth and bones is calcium hydroxyl phosphate. Sources of calcium are milk, fish, milk products and green leafy vegetables. Two percent of the body is calcium. Vitamin D is needed to help the absorption of calcium. Taking calcium carbonate tablets can aid in the digestion of food.
Calcium was used by the ancients as lime. The Romans called limestone (calcium carbonate) calx. It is eight percent of the composition of the crust of the moon. Calcium can be found on the Earth as calcium carbonate, which is found in limestone, chalk, marble, dolomite, eggshells, pearls, coral, stalactites, stalagmites and the shells of some marine animals. Calcium carbonate dissolves in water to form calcium bicarbonate.