Calcium (Ca)

Calcium properties

Atomic number

20

Atomic mass

40.078 u

Category

Alkaline earth metal

Group

2

Period

4

Block

s-block

State at room temp.

Solid

Electronegativity

1

Melting point

1,115 K (841.8 °C)

Boiling point

1,757 K (1,483.8 °C)

Density

1.54 g/cm³

Valence electrons

2

Common charges

+2

Oxidation states

+2

Atomic radius

231 pm

Ionization energy

6.113 eV

Electron affinity

—

Radioactive

No, has stable isotopes

Discovered

1808

Calcium electron configuration

The electron configuration of Calcium (Ca) is [Ar] 4s2. Its 20 electrons are arranged in shells as 2, 8, 8, 2.

Protons, neutrons and electrons in Calcium

A neutral Calcium atom has 20 protons and 20 electrons. Most Calcium atoms have about 20 neutrons: the atomic mass rounded to 40, minus the atomic number 20.

Neutrons are approximate: atoms of the same element can have different numbers of neutrons (isotopes). Atomic number and mass

How many valence electrons does Calcium have?

2

Calcium has 2 valence electrons in its outermost shell, shell 4. These are the electrons involved in chemical bonding.

See every element: Periodic table with valence electrons

Calcium orbital diagram

Each box is an orbital that holds up to two electrons with opposite spins (↑↓). The inner shells are the same as the noble gas in brackets. How to write electron configurations

Molar mass of Calcium

40.078 g/mol

One mole of Calcium atoms (6.022 × 10²³ atoms) has a mass of 40.078 grams. Use this value to convert between grams and moles.

Compounds containing Calcium

Calcium facts

• Calcium is the most abundant metal in the human body, and about 99% of it is stored in bones and teeth.
• Limestone, chalk and marble are all forms of calcium carbonate, and much limestone formed from the shells and skeletons of ancient sea creatures.
• Calcium (Ca) has atomic number 20 and is a solid at room temperature. It was discovered in 1808.

Position in the periodic table

Calcium is element 20, in period 4 and group 2 of the periodic table, in the s-block.

All alkaline earth metals

Uses of Calcium

Calcium compounds are the basis of the construction industry: limestone is heated to make lime and cement, and gypsum (calcium sulfate) is used in plaster and drywall. In steelmaking, lime removes impurities such as phosphorus and silica as slag. Calcium carbonate is used in antacids, calcium supplements and as a filler in paper and plastics, and calcium metal is used to extract other metals from their compounds.

Who discovered Calcium?

Humphry Davy isolated calcium in 1808 in London, by electrolysis of a mixture of lime and mercury(II) oxide. Lime itself, a calcium compound, had been used in building since ancient times.

Where does the name come from?

Calcium comes from the Latin calx (genitive calcis), meaning 'lime', the calcium compound made by heating limestone. Humphry Davy named the metal in 1808 after isolating it from lime.

Discovery timeline