Calcium Element Properties
Complete reference for Calcium (Ca, element 20): atomic data, electron configuration, isotopes, physical constants, and unit converter.
Calcium
Alkaline Earth Metal — Period 4, Group 2
Atomic Identity
Periodic Table Locator — Period 4 Neighborhood (s-block)
Calcium (Z=20) sits between potassium (alkali metal) and scandium (transition metal) in Period 4. It is directly below magnesium (Z=12) and above strontium (Z=38) in Group 2.
Electron Configuration
No unpaired electrons — all orbitals filled
Key Isotopes of Calcium
| Isotope | Symbol | Protons | Neutrons | Mass (u) | Natural Abundance | Stability |
|---|---|---|---|---|---|---|
| Calcium-40 | ⁴⁰Ca | 20 | 20 | 39.9625909 | 96.941% | Stable |
| Calcium-41 | ⁴¹Ca | 20 | 21 | 40.9622779 | Trace/Cosmo. |
Unstable
Electron capture, t½ = 99,400 yr |
| Calcium-42 | ⁴²Ca | 20 | 22 | 41.9586176 | 0.647% | Stable |
| Calcium-43 | ⁴³Ca | 20 | 23 | 42.9587662 | 0.135% | Stable |
| Calcium-44 | ⁴⁴Ca | 20 | 24 | 43.9554816 | 2.086% | Stable |
| Calcium-46 | ⁴⁶Ca | 20 | 26 | 45.9536890 | 0.004% | Stable |
| Calcium-47 | ⁴⁷Ca | 20 | 27 | 46.9545414 | Radioactive |
Unstable
β⁻ decay, t½ = 4.536 d |
| Calcium-48 | ⁴⁸Ca | 20 | 28 | 47.9525228 | 0.187% |
Unstable
ββ decay, t½ ≫ 4×10¹⁹ yr |
Calcium-40 accounts for ~97% of natural calcium. Ca-41 (cosmogenic) is used to date bone ages. Ca-47 is a medical tracer for calcium metabolism studies. Ca-48 is a near-doubly-magic nucleus used in nuclear physics research and neutrinoless double-beta decay experiments.
Physical Properties
Chemical Properties
Ground State Quantum Numbers
Notable Emission Lines
Calcium produces a characteristic brick-red to orange flame in a flame test. The 422.67 nm resonance line is widely used in atomic absorption spectroscopy (AAS) for calcium analysis.
Property Unit Converter
Convert common Calcium property values between units. Enter a value and select the conversion.
Common Calcium Compounds
| Compound | Formula | Common Name | Key Uses |
|---|---|---|---|
| Calcium carbonate | CaCO₃ | Limestone / chalk / marble | Cement, glass, antacid (Tums), toothpaste, paper filler |
| Calcium oxide | CaO | Quicklime | Cement production, steel slag treatment, water treatment |
| Calcium hydroxide | Ca(OH)₂ | Slaked lime / limewater | Mortar, plaster, soil pH adjustment, water softening |
| Calcium sulfate | CaSO₄·2H₂O | Gypsum | Drywall (plasterboard), plaster of Paris, soil conditioner |
| Calcium phosphate | Ca₃(PO₄)₂ | Tricalcium phosphate | Bone and teeth mineral, fertilizer, food supplement |
| Calcium chloride | CaCl₂ | Calcium chloride | De-icing roads, food additive (E509), desiccant, concrete accelerant |
| Calcium fluoride | CaF₂ | Fluorite / fluorspar | Optical lenses, UV windows, HF production, steel flux |
| Calcium silicate | Ca₂SiO₄ | Belite | Portland cement clinker, fireproofing, calcium silicate board |
Key Facts About Calcium
Most Abundant Mineral in the Body
Calcium is the most abundant mineral in the human body by mass — about 1 kg in an average adult. Approximately 99% is stored as hydroxyapatite in bones and teeth. The remaining 1% in blood and cells governs muscle contraction, nerve transmission, hormone release, and blood clotting via intracellular Ca²⁺ signaling.
Foundation of Cement and Concrete
Limestone (CaCO₃) is the primary raw material for Portland cement, the most widely used construction material on Earth. Heating limestone produces quicklime (CaO), which reacts with water to form slaked lime Ca(OH)₂. When combined with silicates in cement clinker, calcium silicate hydrate phases form the binding matrix of concrete.
Fifth Most Abundant in Earth's Crust
At ~3.6% of Earth's crust by mass, calcium is the fifth most abundant element overall (after oxygen, silicon, aluminum, and iron) and the most abundant alkaline earth metal. It occurs naturally as calcite, aragonite (both CaCO₃), gypsum (CaSO₄·2H₂O), fluorite (CaF₂), and dolomite (CaMg(CO₃)₂).
Strongly Reducing Metal
With a standard electrode potential of −2.868 V, calcium is a powerful reducing agent — more reactive than magnesium but less than sodium. It reduces most metal oxides and halides at high temperature, making it useful for producing refractory metals such as thorium, uranium, and chromium by thermite-style metallothermic reduction.
Brick-Red Flame Test
Calcium gives a distinctive brick-red (orange-red) flame in the flame test, a simple but reliable qualitative test used to identify Ca²⁺ ions. The color arises from the 616 nm and 622 nm emission lines of electronically excited calcium atoms. This property is also exploited in red signal flares and some firework formulations.
Isolated by Electrolysis
Calcium was first isolated in 1808 by Humphry Davy using electrolysis of a calcium mercury amalgam, the same year he isolated strontium, barium, and magnesium. The name comes from the Latin calx, meaning lime — the material (calcium oxide) known and used since antiquity for mortar and plaster.
Summary
Complete reference for Calcium (Ca, element 20): atomic data, electron configuration, isotopes, physical constants, and unit converter.
How it works
- Browse the atomic identity section for symbol, atomic number, and standard atomic weight.
- Check the electron configuration panel for orbital notation and quantum numbers.
- Review the isotopes table for stable and notable radioactive isotopes with natural abundances.
- Consult the physical and chemical properties panels for melting point, density, ionization energies, and more.
- Use the interactive unit converter to convert calcium property values between common units.
- Explore the mini periodic table locator to visualize where calcium sits among neighboring elements.
Use cases
- Look up calcium constants for chemistry homework or exams.
- Verify atomic data when writing lab reports or research papers.
- Reference isotope data for nuclear chemistry or geochronology (calcium-41, calcium-48) research.
- Convert melting and boiling points between Celsius, Fahrenheit, and Kelvin.
- Teach or learn alkaline earth metal properties using calcium as an example.
- Confirm electron configuration before writing molecular orbital or Lewis dot diagrams.
- Research calcium compounds for pharmaceutical, construction, or materials science work.
- Quick-reference ionization energies for electrochemistry or spectroscopy calculations.