Element: Calcium
General data
| Element name | Calcium |
|---|---|
| Chemical symbol | Ca |
| Atomic number Z | 20 |
| Year discovered | known since antiquity |
| Standard state (25°C) | Solid |
| Category | Alkaline earth metal |
| Block | s |
| Atomic mass | 40.078 |
| CPK color | #3DFF00 |
Physical properties
| Melting point | 1115 K (842 °C) |
|---|---|
| Boiling point | 1757 K (1484 °C) |
| Density | 1.54 g/cm³ |
Energy properties
| First ionization energy | 6.113 eV |
|---|---|
| Electron affinity | no data |
Atomic structure
| Protons | 20 (Atomic number) |
|---|---|
| Neutrons (Ca-40, most abundant isotope) | 20 |
| Electrons | 20 |
| Electron configuration | [Ar] 4s² |
| Oxidation states | +2 |
| Electronegativity (Pauling) | 1 |
| Atomic radius (van der Waals) | 231 pm |
Ionization energies - NIST ASD (20 states)
| State | Charge | Ioniz. energy (eV) | Type |
|---|---|---|---|
| Ca I | 0+ | 6.113154921 ± 0.0000000005 | measured |
| Ca II | 1+ | 11.871719 ± 0.000004 | measured |
| Ca III | 2+ | 50.91316 ± 0.00025 | measured |
| Ca IV | 3+ | 67.2732 ± 0.0021 | semi-empirical |
| Ca V | 4+ | 84.34 ± 0.08 | semi-empirical |
| Ca VI | 5+ | 108.78 ± 0.25 | semi-empirical |
| Ca VII | 6+ | 127.21 ± 0.25 | semi-empirical |
| Ca VIII | 7+ | 147.24 ± 0.12 | measured |
| Ca IX | 8+ | 188.54 ± 0.06 | semi-empirical |
| Ca X | 9+ | 211.275 ± 0.004 | semi-empirical |
| Ca XI | 10+ | 591.6 ± 0.12 | semi-empirical |
| Ca XII | 11+ | 658.2 ± 0.9 | semi-empirical |
| Ca XIII | 12+ | 728.6 ± 1.1 | semi-empirical |
| Ca XIV | 13+ | 817.2 ± 0.6 | semi-empirical |
| Ca XV | 14+ | 894 ± 0.4 | semi-empirical |
| Ca XVI | 15+ | 973.7 ± 0.3 | semi-empirical |
| Ca XVII | 16+ | 1086.8 ± 0.4 | semi-empirical |
| Ca XVIII | 17+ | 1157.726 ± 0.007 | calculated |
| Ca XIX | 18+ | 5128.8576 ± 0.0003 | calculated |
| Ca XX | 19+ | 5469.86358 ± 0.00006 | calculated |
Value type as given by NIST ASD: measured - from evaluated experimental data; calculated - from ab initio calculations (mostly highly ionised atoms that have not been measured; for the simplest ones, e.g. H I, the calculation is more accurate than measurement); semi-empirical - from interpolation, extrapolation or another semi-empirical method.
Photos
Isotopes (26)
| A | N | Half-life | Decay |
|---|---|---|---|
| Ca-35 | 15 | 25.7 ms | EC/β⁺ |
| Ca-36 | 16 | 100.8 ms | EC/β⁺ |
| Ca-37 | 17 | 181.0 ms | EC/β⁺ |
| Ca-38 | 18 | 443.8 ms | EC/β⁺ |
| Ca-39 | 19 | 860.3 ms | EC/β⁺ |
| Ca-40 | 20 | stable | - |
| Ca-41 | 21 | 99400 a | EC |
| Ca-42 | 22 | stable | - |
| Ca-43 | 23 | stable | - |
| Ca-44 | 24 | stable | - |
| Ca-45 | 25 | 162.61 d | β⁻ |
| Ca-46 | 26 | stable | - |
| Ca-47 | 27 | 4.536 d | β⁻ |
| Ca-48 | 28 | 5.6×10¹⁹ a | 2β⁻ |
| Ca-49 | 29 | 8.718 min | β⁻ |
| Ca-50 | 30 | 13.45 s | β⁻ |
| Ca-51 | 31 | 10.0 s | β⁻ |
| Ca-52 | 32 | 4.6 s | β⁻ |
| Ca-53 | 33 | 460 ms | β⁻ |
| Ca-54 | 34 | 90 ms | β⁻ |
| Ca-55 | 35 | 22 ms | β⁻ |
| Ca-56 | 36 | 11 ms | β⁻ |
| Ca-57 | 37 | unknown | β⁻ |
| Ca-58 | 38 | unknown | β⁻ |
| Ca-59 | 39 | unknown | β⁻ |
| Ca-60 | 40 | unknown | β⁻ |
Data sources
- PubChem Periodic Table API - Retrieved on 29 June 2026 - licence: CC0
- IUPAC CIAAW - Abridged Standard Atomic Weights 2024 - Table version: 2024 - licence: Public domain
- NNDC Wallet Cards 2023 - Data as of 15 October 2024 - licence: Public domain
- NIST Atomic Spectra Database (ASD) - Retrieved on 29 June 2026 - licence: © U.S. Secretary of Commerce
- Images of Elements - Retrieved on 29 June 2026 - licence: CC BY 3.0