Calcium
Calcium is a soft, grey alkaline earth metal that never turns up on its own in nature — it's simply too reactive, and instead spends its existence locked inside compounds like limestone, chalk, and gypsum. Those compounds have shaped human life since ancient times, long before anyone understood calcium as a distinct chemical element.
- Group · Period
- 2 · 4
- At room temp
- solid
- Melts at
- 1115 K
- Density
- 1.54 g/cm³
- Discovered
- Ancient
Uses
Calcium compounds are everywhere in construction and industry: limestone and gypsum are essential raw materials for cement, plaster, and mortar, and crushed limestone underpins much of the concrete used in modern buildings and roads. Calcium carbonate also serves as an antacid, neutralizing stomach acid, and as a common dietary supplement for bone health, alongside calcium-rich foods like dairy products and leafy greens. In steelmaking, calcium is added in small amounts to help remove impurities from molten metal.
Beyond industry, calcium is a fundamentally biological element — it’s the main structural mineral in bones and teeth, and calcium ions also trigger muscle contractions and play a central role in blood clotting.
History
Calcium compounds such as lime and gypsum have been used by humans since antiquity, from ancient plaster and mortar to early medicine, long before calcium was recognized as a distinct chemical element. It wasn’t until 1808 that English chemist Humphry Davy isolated metallic calcium for the first time, using electrolysis on a mixture of lime and mercury oxide — the same technique he’d used to isolate potassium and sodium the year before. Its name comes from “calx,” the Latin word for lime, reflecting the long-familiar compound that finally gave up its metal.
Fun facts
- Calcium is the fifth most abundant element in Earth's crust, mostly bound up in limestone, marble, and other carbonate rocks.
- About 99% of the calcium in the human body is stored in bones and teeth, where it provides structural strength.
- Because it reacts readily with air and water, calcium metal is never found free in nature — only its compounds occur naturally.
Frequently asked questions
If calcium compounds have been used since ancient times, why is the pure element a relatively recent discovery?
Because calcium is so reactive, it never occurs as a free metal in nature — ancient builders and chemists only ever encountered it locked inside compounds like lime and gypsum, which is why materials made from calcium go back millennia. Prying the pure metal out of those compounds requires a strong enough reaction, which is a much more modern chemical achievement.
Why is calcium so important for bones and teeth?
Bones and teeth are built largely from calcium phosphate, a hard mineral that gives them their rigidity. The body carefully regulates calcium levels in the blood, and if dietary calcium runs short, it will pull calcium out of bone to keep other vital functions running, which over time can weaken the skeleton.
Is calcium a metal?
Yes — it's classified as an alkaline earth metal, sharing the group with elements like magnesium and barium. It's relatively soft and light for a metal, and like its neighbors it reacts readily with water and air, which is part of why pure calcium metal is rarely seen outside a laboratory or industrial setting.
Compounds
4 notable compounds containing Ca
- CaCO3mineral
Calcium carbonate
An ionic carbonate salt found naturally as limestone, chalk, and marble, and as the structural material of seashells and coral.
Used for: Antacid tablets, cement and construction, calcium supplement
- CaCl2salt
Calcium chloride
A highly water-soluble ionic salt that releases heat as it dissolves and readily pulls moisture from the air. It forms colorless, brittle crystals when dry.
Used for: De-icing roads and sidewalks, food preservative, drying agent
- CaF2mineral
Calcium fluoride
An ionic salt found naturally as the mineral fluorite, which crystallizes in cubes and often fluoresces under ultraviolet light.
Used for: Source of fluorine and hydrofluoric acid, optical lenses, steel flux
- Ca3(PO4)2mineral
Calcium phosphate
An ionic salt that, in its hydroxyapatite form, makes up the mineral structure of bones and teeth.
Used for: Fertilizer, dietary supplement, food additive
Isotopes
25 known isotopes
Swipe to see all columns →
| Isotope | Natural abundance | Half-life | Decay mode | Mass excess | Binding energy / nucleon | Decay width |
|---|---|---|---|---|---|---|
| Ca-40 stable | 96.941% | Stable | — | -34,846.4 keV | 8,551.3 keV | — |
| Ca-42 stable | 0.647% | Stable | — | -38,547.29 keV | 8,616.56 keV | — |
| Ca-43 stable | 0.135% | Stable | — | -38,408.87 keV | 8,600.67 keV | — |
| Ca-44 stable | 2.086% | Stable | — | -41,468.73 keV | 8,658.18 keV | — |
| Ca-46 stable | 0.004% | Stable | — | -43,139.61 keV | 8,668.98 keV | — |
| Ca-48 | 0.187% | 2.9E19 Y | Double beta-minus decay (78%), Double beta-minus decay (74%), Beta-minus decay (22%) | -44,224.87 keV | 8,666.69 keV | 4.99 × 10-43 eV |
Show all 25 isotopes
| Ca-34 | — | 35 ns | Proton emission, Two-proton emission | 14,890 keV | 7,173 keV | 1.30 × 10-8 eV |
| Ca-35 | — | 25.7 ms | Electron capture / beta-plus decay (100%), ECP (95.9%), EC2P (4.1%) | 5,190 keV | 7,476 keV | 1.78 × 10-14 eV |
| Ca-36 | — | 101.2 ms | Electron capture / beta-plus decay (100%), ECP (51.2%) | -6,451.17 keV | 7,815.88 keV | 4.51 × 10-15 eV |
| Ca-37 | — | 181.1 ms | Electron capture / beta-plus decay (100%), ECP (82.1%) | -13,136.07 keV | 8,003.46 keV | 2.52 × 10-15 eV |
| Ca-38 | — | 443.76 ms | Electron capture / beta-plus decay (100%) | -22,058.5 keV | 8,240.04 keV | 1.03 × 10-15 eV |
| Ca-39 | — | 860.3 ms | Electron capture / beta-plus decay (100%) | -27,282.71 keV | 8,369.67 keV | 5.30 × 10-16 eV |
| Ca-41 | — | 9.94E+4 Y | Electron capture (100%) | -35,137.91 keV | 8,546.71 keV | 1.45 × 10-28 eV |
| Ca-45 | — | 162.61 d | Beta-minus decay (100%) | -40,812.23 keV | 8,630.55 keV | 3.25 × 10-23 eV |
| Ca-47 | — | 4.536 d | Beta-minus decay (100%) | -42,344.67 keV | 8,639.35 keV | 1.16 × 10-21 eV |
| Ca-49 | — | 8.718 m | Beta-minus decay (100%) | -41,300 keV | 8,594.85 keV | 8.72 × 10-19 eV |
| Ca-50 | — | 13.45 s | Beta-minus decay (100%) | -39,589.23 keV | 8,550.16 keV | 3.39 × 10-17 eV |
| Ca-51 | — | 10.0 s | Beta-minus decay (100%), Beta-minus, neutron emission | -36,332.31 keV | 8,476.91 keV | 4.56 × 10-17 eV |
| Ca-52 | — | 4.6 s | Beta-minus decay (100%), Beta-minus, neutron emission | -34,266.27 keV | 8,429.38 keV | 9.92 × 10-17 eV |
| Ca-53 | — | 461 ms | Beta-minus decay (100%), Beta-minus, neutron emission (40%) | -29,387.71 keV | 8,330.58 keV | 9.90 × 10-16 eV |
| Ca-54 | — | 107 ms | Beta-minus decay (100%), B-2N, Beta-minus, neutron emission | -25,160.59 keV | 8,247.5 keV | 4.26 × 10-15 eV |
| Ca-55 | — | 22 ms | Beta-minus decay (100%), B-2N, Beta-minus, neutron emission | -18,650.38 keV | 8,125.93 keV | 2.07 × 10-14 eV |
| Ca-56 | — | 11 ms | Beta-minus decay (100%), Beta-minus, neutron emission, B-3N | -13,510.39 keV | 8,033.17 keV | 4.15 × 10-14 eV |
| Ca-57 | — | 620 ns | B-2N, Beta-minus, neutron emission, Beta-minus decay | -6,560 keV | 7,912 keV | 7.36 × 10-10 eV |
| Ca-58 | — | 620 ns | Beta-minus, neutron emission, Beta-minus decay | -1,530 keV | 7,828 keV | 7.36 × 10-10 eV |