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A basic diagram of the element calcium, an atom comprised of 20 protons, 20 neutrons, and 20 electrons.

In chemistry, calcium (TR:40) (LH:12) (TL:52), symbol Ca, the 20th element (Z:20) of the periodic table, is an atom, with a mass of 40.08 amu, comprised of 20 protons, 20 neutrons, and 20 electrons; with an electron configuration of: [Ar] 4s2.


See main: Elemental composition of humans; Thims periodic table

The following is an early estimate of the percent calcium in humans:

“The human body contains carbon 13.5%, hydrogen 9.1%, oxygen 72%, nitrogen 2.5%, phosphorus 1.15%, sodium 0.1 %, calcium 1.3%, magnesium 0.001%, iron 0.01%, and traces of silicon and fluorine.”
— Carl Kelsey (1916), The Physical Basis of Society (pg. 7) [1]

Presently, it is known that in humans, sodium is the 5th most dominant element, by mass composition (1.4% mass), of the 26-elements in the standard human molecular formula.[2]

End matter


  1. Kelsey, Carl. (1916). The Physical Basis of Society (pg. 7). D. Appleton and Company.
  2. Thims, Libb. (2008). The Human Molecule (GB) (Amz) (Iss) (elemental composition table, pgs. 52-55). LuLu.

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