Atomic No Of Calcium

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  1. Atomic No Of Calcium Phosphate
  2. Atomic No Of Calcium
  3. Atomic No Of Calcium Nitrate
  4. Atomic No Of Calcium Acetate

The official atomic number of calcium is 20, it’s symbol is ‘Ca’, it’s atomic mass is 0.0004 u and it’s atomic configuration is Ar 4s2. That’s all the basics of calcium, and to go even deeper: it was discovered in 1808 by Humphrey Davy and it’s melting point is 842 degrees celcius (1547 degrees Fahrenheit). The atomic mass is useful in chemistry when it is paired with the mole concept: the atomic mass of an element, measured in amu, is the same as the mass in grams of one mole of an element. Thus, since the atomic mass of iron is 55.847 amu, one mole of iron atoms would weigh 55.847 grams.

Calcium is an alkaline earth metal and has been known since prehistoric times. It was discovered in 1787 by Antoine Lavoisier and was isolated in pure form in 1808. Calcium is important nutrient for the human body.

Discovery and History

The history of calcium dates to 7000 BC, when calcium in the form of lime was used as plasters for making statues and as building material. The name calcium is derived from the word “calx” that is Latin for lime. Another form of calcium, calcium sulphate that is termed as gypsum have been found to be used in the construction of Great Egyptian Pyramid of Giza. Later in 1787, lime was considered as an oxide of a novel chemical element by Antoine Lavoisier. Calcium was first isolated by Sir Humphry Davy in 1808 in England. He electrolyzed a mixture of lime and mercuric oxide [1]. A few other scientists, Magnus Pontin and Jöns Jacob Berzelius also produce a calcium amalgam after performing electrolysis on a mixture of lime and mercury oxide.


Periodic Table ClassificationGroup 2
Period 4
State at 20CSolid
Electron Configuration[Ar] 4s2
Electron Number20
Proton Number20
Electron Shell 2, 8, 8, 2
Density1.55 at 20°C
Atomic number20
Atomic Mass40.08 g.mol -1
Electronegativity according to Pauling1.00


Calcium is very reactive and does not occur in free form. It occur in earth’s crust in the forms of carbonate, sulfate, fluoride, silicate and borate. The calcium carbonate occurs in marble, chalk, limestone and calcite. Calcium sulfate (CaSO4) occurs in anhydrite and gypsum, calcium fluoride in fluorspar or fluorite (CaF2) and calcium phosphate occurs in apatite. Calcium also occurs in numerous silicates and alumino silicates. Almost all natural waters, including seawater, contain either or both calcium carbonate and calcium sulfate. Many organisms concentrate calcium compounds in their shells or skeletons. For example calcium carbonate is formed in the shells of oysters and in the skeletons of coral. [2]

Physical characteristics

Its physical and chemical properties are most similar to strontium and barium. It is the fifth most abundant element in Earth’s crust and the third most abundant metal, after iron and aluminum. The atomic number of calcium is 20, and atomic weight is 40.078. The density of calcium is 1.55 grams per cubic centimeter. Its melting point is 842 °C and boiling point is 1494 °C. Calcium is harder than lead but can be cut with a knife with effort. Calcium is a poorer conductor of electricity than copper or aluminum (by volume), but it is a better conductor by mass due to its very low density. [3] It reacts with atmospheric oxygen, which makes its unfavorable to be used in the most applications, but its usage is space is being considered such in space. [4]

Chemical characteristics

The chemistry of calcium is similar to heavy alkaline earth metal. The metal reacts slowly with oxygen, water vapor, and nitrogen of the air to form a yellow coating of the oxide, hydroxide, and nitride. It burns in air or pure oxygen to form the oxide and reacts rapidly with warm water to produce hydrogen gas and calcium hydroxide. On heating, calcium reacts with hydrogen, halogens, boron, sulfur, carbon, and phosphorus. Although it compares with sodium as a reducing agent, calcium is more expensive and less reactive than the latter. In many deoxidizing, reducing, and degasifying applications, however, calcium is preferred because of its lower volatility and is used to prepare chromium, thorium, uranium, zirconium, and other metals from their oxides. [5] Calcium metal dissolves directly in liquid ammonia to give a dark blue solution. [6] Due to the large size of the Ca2+ ion, high coordination numbers are common.

Uses and Significance

  • Calcium carbonate is taken as an antacid is effective for treating indigestion.
  • Giving calcium gluconate intravenously (by IV) can reverse hyperkalemia, a condition in which there is too much potassium in the blood.
  • Taking calcium by mouth is effective for treating and preventing hypocalcemia. It is also given intravenously (by IV) for treating very low levels of calcium in the body.
  • Taking calcium carbonate or calcium acetate by mouth is effective for controlling high phosphate levels in the blood, that is present in people with kidney failure.
  • Taking calcium by mouth is effective for preventing bone loss and treating osteoporosis.
  • Calcium is a co-factor for many enzymes which makes it’s a vital component of the biological system.
  • Calcium affects the smooth muscle that surrounds blood vessels and cause it to relax. There are various ionic channels in the membrane of living cells that are controlled by level of calcium in the body.
  • It is important to note that calcium is not easily absorbed without the presence of vitamin D.


There are six natural isotopes of calcium, including; Ca-40 is most abundant (97 percent of natural abundance), Ca-44 (2 percent of natural abundance); Ca-42 (0.6 percent of natural abundance); Ca-48 is most stable (0.2 percent of natural abundance); Ca-43 (0.1 percent of natural abundance); Ca-46 (0.004 percent of natural abundance). It is the first element to have low density and have six natural isotopes.


3. Ropp, Richard C. (31 December 2012). Encyclopedia of the Alkaline Earth Compounds. pp. 12–5. ISBN 978-0-444-59553-9.
4. Hluchan and Pomerantz, p. 484
6. Greenwood and Earnshaw, pp. 112–3

Other Periodic Table Elements

  • Erbium

    Erbium was discovered in 1843. Its pink colored Er3+ ions have fluorescent properties useful in…

  • Holmium

    Holmium was discovered in 1878. It has highest magnetic moment that is why it is…

  • Francium

    Francium was discovered in 1939. It is very unstable alkali metal and considered the second…


  • Atomic number and Mass number
  • Isotopes


An atom is the smallest particle of an element which can take part in chemical reaction. Atom consists of three fundamental particles i.e. proton, neutron and electron. Atoms of same elements are similar in properties whereas atoms of different elements are different in properties. Example:- ‘H’ represent the atom of hydrogen.

Proton is positively charged and electron is negatively charged particle. In an atom, number of protons = number of electrons. Hence, the net charge present in an atom is zero i.e. a free atom is chargeless.

Atomic number and Mass number

Atomic no. of potassium
Atomic number :
  • Atomic number is the number of protons present in an atom.
  • The modern periodic table is arranged in order of increasing atomic number.
Mass number and Atomic mass :
  • Mass number is the sum of the number of protons and the number of neutrons present in an atom. It is a whole number.

Mass no. of an atom = No. of protons + No. of neutrons

Atomic No Of Calcium Phosphate

  • Atomic mass is the average mass of the all of the isotopes of that element. It is a decimal number.
  • For example: Hydrogen has three isotopes – 1H1, 1H2 and 1H3 having mass number 1, 2 and 3 respectively. Naturally occurring hydrogen contains about 99.985% of protium, 0.014% of deuterium and 0.001 % of tritium. Therefore the atomic mass of hydrogen is 1.00784 amu.
  • The atomic mass of an element element is measured in atomic mass unit (amu, also known as Daltons ‘ D’or unified atomic mass unit ‘u’).
  • 1amu = 1.66 x 10-24 grams. 1gm = 6.022 x 1023 amu ( i.e. Avogadro’s number).


  • Atomic number = Number of protons = Number of electrons = 13
  • Mass number = No. of protons + No. of neutrons
  • No. of neutrons = Mass number – No. of protons = 27-13 = 14.
Atomic mass of first 20 elements
Atomic numberElementAtomic mass


Atoms of the same element having same atomic number but different mass number (atomic mass/weight) are called isotopes. For example:

Isotopes of hydrogen :

There are three isotopes of hydrogen:

  1. Protium or ordinary hydrogen
  2. Deuterium or heavy hydrogen
  3. Tritium or radioactive hydrogen.
Name ProtiumDeuteriumTritium
Symbol1H or H2H or D3H or T
No. of protons(P)111
No. of neutrons(n)012
No. of electrons(e)111
Atomic no.(Z)111
Mass no.(A)123

Naturally occurring hydrogen contains about 99.985% of protium, 0.014% of deuterium and 0.001 % of tritium.

Isotopes have different physical properties since they differ in their mass number.

They have same chemical properties since their electronic configuration is same. However, they differ in the rate of chemical reaction. For example, D2 reacts with Cl2 about 13 times slower than H2 does. The different in rate of reaction due to difference in mass of the atoms of the same element is called isotope effect.

Some other examples of isotopic elements :

Atomic No Of Calcium

ElementsIsotopesMost abundant isotope
Carbon6C12, 6C13, 6C146C12
Nitrogen7N14, 7N157N14
Oxygen8O16, 8O17, 8O188O16
Sulphur16S32, 16S33, 16S34, 16S3616S32
Chlorine17Cl35, 17S3717Cl35


Atoms of different elements having different atomic number but same mass number are called isobars. For example :

18Ar40, 19K40 and 20Ca40

Atomic No Of Calcium Nitrate


Atoms of different elements having different atomic number and mass number but same number of neutrons are called isotones. For example :

6C14, 7N15 and 8O16

Objective questions and their answers


1. Which of the following is known as heavy hydrogen?

a. Protium c. Tritium

b. Deuterium d. Para hydrogen

2. Which of the following is known as radioactive hydrogen?

a. Protium c. Tritium

b. Deuterium d. Para hydrogen

3. Least abundant isotope of hydrogen is:

a. Protium c. Tritium

b. Deuterium d. Heavy hydrogen

4. Diamond and graphite are :

a. Isotopes c. Isotones

b. Isobars d. Allotropes

Atomic no of calcium nitrate

5. 6C14 and 8O16 are :

a. Isotopes c. Isotones

b. Isobars d. Allotropes

6. 6C14 and 7N14 are :

a. Isotopes c. Isotones

b. Isobars d. Allotropes

7. All particles residing inside the nucleus of an atom are termed as:

a. Protons c. Electrons

b. Neutrons d. Nucleons

8. What makes the atomic mass fractional ?

a.Prerence of isotopes

b. Number of unpaired electrons

c. Spherical shape

d. Quantum number.

9. Which of the following are not isotopes:

a. 1H1 and 1H3

b. 18K40 and 20Ca40

Atomic No Of Calcium Acetate

c. 6C14 and 7N14

d. Both b and c.

10. Charge present in the nucleus of an atom is :

a. Positive c. Chargeless

b. Negative d. Both +Ve and -Ve

11. Molecular weight of heavy water is :

a. 16 c. 20

b. 18 d. 22

Answers :

1. b 2. c 3. c

4. d [Note : different forms of same element having different properties are called allotropes]

5. c 6. b 7. d

8. a 9. d 10. a

11. c Note :Heavy waterDeuterium oxide (D2O) is called heavy water. It’s molecular weight is 20 and boiling paint is 101.50C and melting point is 3.80C.


  • Sthapit, M.K., Pradhananga, R.R., Foundations of Chemistry, Vol 1 and 2, Fourth edition, Taleju Prakashan, 2005.