20Ca40.08
Calcium
Alkaline Earth Metal
Solid at STP
Period 4Group 2Block SDiscovered Ancient
[Ar]4s2
Calcium is a chemical element with symbol Ca and atomic number 20. Calcium is a soft gray alkaline earth metal, fifth-most-abundant element by mass in the Earth's crust. The ion Ca2+ is also the fifth-most-abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride, magnesium, and sulfate.
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Atomic Properties
| Atomic Number | 20 |
| Atomic Mass | 40.08 u |
| Electron Configuration | [Ar]4s2 |
| Oxidation States | +2 |
| Electronegativity | 1 (Pauling) |
| Atomic Radius | 231 pm |
| Ionization Energy | 6.113 eV |
| Block | S |
Physical Properties
| Standard State | Solid |
| Melting Point | 1115 K (841.9 °C) |
| Boiling Point | 1757 K (1483.8 °C) |
| Density | 1.54 g/cm³ |
| Molar Heat | 25.929 J/(mol·K) |
| CPK Color | #3DFF00 |
Classification
| Category | Alkaline Earth Metal |
| Group Block | Alkaline earth metal |
| Period | 4 |
| Group | 2 |
| Block | S |
Discovery
| Year Discovered | Ancient |
| Discovered By | Humphry Davy |
| Electron Shells | 2, 8, 8, 2 |