Calcium (Ca)
Element 20 · Alkaline earth metal · Solid at 25 °C · Group 2, Period 4
Calcium builds bones, teeth, seashells, and limestone, and calcium compounds set into the cement and concrete of the built world.
On the periodic table, calcium sits in group 2 — the alkaline earth metals — in period 4. It is one of 6 elements classified as an alkaline earth metal, and at room temperature (25 °C) it is a solid.
The alkaline earth metals carry two outer electrons and form 2+ ions in almost all of their chemistry. They are harder, denser, and less violently reactive than their alkali-metal neighbors in group 1, but still too reactive to occur uncombined in nature. Their compounds are everywhere — in limestone, bones, fireworks, and lightweight alloys.
Properties of calcium
| Atomic number (Z) | 20 |
|---|---|
| Symbol | Ca |
| Atomic mass | 40.078 |
| Category | Alkaline earth metal |
| Group | 2 |
| Period | 4 |
| Block | s-block |
| Metal / nonmetal | Metal |
| State at 25 °C | Solid |
| Electron configuration | [Ar] 4s2 |
| Electronegativity (Pauling) | 1 |
| Melting point | 842 °C (1,115.15 K / 1,547.6 °F) |
| Boiling point | 1,484 °C (1,757.15 K / 2,703.2 °F) |
| Density | 1.55 g/cm³ |
Position in the periodic table
Calcium shares group 2 — the alkaline earth metals with Beryllium (Be), Magnesium (Mg), Strontium (Sr), Barium (Ba), Radium (Ra). Elements in the same group have the same number of outer electrons, so they tend to behave alike chemically — comparing them is one of the fastest ways to see periodic trends in action.
Physical properties
Calcium melts at 842 °C (1,115.15 K / 1,547.6 °F) and boils at 1,484 °C (1,757.15 K / 2,703.2 °F), giving it a liquid range of about 642 °C at standard pressure.
Its density is 1.55 g/cm³.
See also: the interactive periodic table, how to read the periodic table, the element families tour.