Element identity
Atomic number, symbol, relative atomic mass display and periodic position are established reference data.
Atomic / electronic model
Ground-state electron configuration and atomic reference values are compiled/evaluated data; orbital graphics are teaching probability models, not photographs.
Material / molecular structure
The displayed ordinary structure is based on established material or molecular science; simplified viewers are labelled as teaching schematics where exact crystallographic coordinates are not rendered.
Temperature / phase path
Transition values are reference/evaluated values for the stated teaching path; pressure, purity and allotropy can matter.
Geography
Real pins use reviewed place/dataset context. Conceptual layers are used when country pins would imply false occurrence, unsafe inventory or an incomplete global distribution.
The lens describes evidence status, not confidence theatre. “Unknown” is kept unknown, and teaching schematics are not presented as direct measurements.
Calcium (Ca)
Calcium is a reactive alkaline-earth metal whose two outer 4s electrons connect Group 2 position to Ca²⁺ chemistry. In nature it is overwhelmingly found in compounds—from limestone and gypsum to the mineral phase of bones and teeth.
Calcium atomic number, mass, protons, electrons and valence electrons
Calcium: quick answers
How many protons, neutrons and electrons does calcium have?
Calcium’s atomic number is 20, so every calcium atom has 20 protons, and a neutral atom also has 20 electrons. Its most common natural isotope, calcium-40, has 20 neutrons (other isotopes have different neutron counts).
What is the symbol for calcium?
The chemical symbol for calcium is Ca.
Is calcium a solid, liquid or gas at room temperature?
Calcium is a solid at room temperature (about 25 °C).
What family (group) is calcium in?
Calcium is an alkaline earth metal, in group 2, period 4 of the periodic table.
How many valence electrons does calcium have?
Calcium has 2 valence electrons, the electrons in its outer shell, which matches its position in group 2.
What is the electron configuration of calcium?
The ground-state electron configuration of calcium is [Ar] 4s².
From atomic number to chemistry
Read these as a chain of causes, not as isolated facts. Each step links to the concept hub if you want the underlying idea explained.
Twenty protons define calcium; a neutral calcium atom also has 20 electrons.
Two outer 4s electrons connect calcium to Group 2 chemistry.
Calcium sits with the alkaline-earth metals and commonly forms Ca²⁺.
Loss of the two outer 4s electrons leaves an argon-like closed-shell ion.
Calcium group, period and position in the periodic table
Calcium is the Group 2 member of Period 4. Potassium is immediately to its left and scandium to its right; magnesium and strontium are its nearest Group 2 neighbors.
Calcium Visual Lab
Decode the tile, compare neutral Ca with Ca²⁺, rotate a calcium-40 teaching nucleus and FCC crystal, inspect orbital-shape approximations, then connect calcium to familiar materials and biology.
Every mark points to one exact feature
Use the numbered tile as a compact reading key: identity, configuration, crystal and physical state are explained again in the interactive sections below.
Calcium in one minute
Two outer electrons. [Ar] 4s² explains the strong tendency to form Ca²⁺.
Compounds dominate nature. Limestone, gypsum and silicate minerals contain calcium.
Biological structure. Calcium phosphates help build bones and teeth.
FCC metal. Calcium’s ordinary metallic crystal is face-centred cubic.
Several stable isotopes. ⁴⁰Ca dominates natural calcium, but five other stable isotopes occur.
2 · 8 · 8 · 2 electrons
Losing both 4s electrons leaves an 18-electron argon-like configuration.
[Ar] 4s²
They are the outer electrons most readily removed in simple calcium chemistry.
Where do I meet calcium?
Clickable cards connect Ca²⁺ chemistry to minerals, biology and materials.
Why can reactive calcium build stable bones and limestone?
Metallic Ca and Ca²⁺ are not the same material
Elemental calcium metal readily reacts, but in calcium carbonate or calcium phosphate the calcium is already present as Ca²⁺ inside a stable ionic/covalent solid framework.
Chemistry turns an ion into a structural resource
In bones and teeth, calcium is incorporated mainly into calcium-phosphate mineral phases rather than existing as free metal. Biology controls where and how the mineral is deposited.
RSC / biological mineral contextWhere is calcium found?
Calcium is widespread in Earth’s crust and natural waters, almost always chemically combined. The modes below are conceptual occurrence layers, not a mine-ranking map.
Calcium among the alkaline-earth metals
Calcium follows the recurring Group 2 outer-electron pattern, but moving down the group changes atomic size and the energy needed to remove those outer electrons.
| Atomic no. | 12 |
|---|---|
| Outer pattern | 3s² |
| Common ion | Mg²⁺ |
| Atomic no. | 20 |
|---|---|
| Outer pattern | 4s² |
| Common ion | Ca²⁺ |
| Atomic no. | 38 |
|---|---|
| Outer pattern | 5s² |
| Common ion | Sr²⁺ |
Calcium atomic, physical, thermal, electrical, chemical and isotope data
Calcium keeps the Magnesium-family depth while preserving its important α-FCC → β-BCC solid transition.
| Atomic number | 20 | NIST / RSC reference | Evaluated |
|---|---|---|---|
| Relative atomic mass | 40.078 | Natural isotope-weighted value | Evaluated |
| Electron configuration | [Ar] 4s² | Neutral ground-state atom | Evaluated |
| 1st ionization energy | ≈589.8 kJ/mol | NIST atomic reference | Evaluated |
| Electronegativity | 1.00 | Pauling scale | Evaluated |
| State at 20 °C | Solid metal | Ordinary-condition reference | Measured |
|---|---|---|---|
| Density | ≈1.55 g/cm³ | Near room temperature | Evaluated |
| Low-temperature crystal | α-Ca · FCC | Below the solid-solid transition | Measured |
| High-temperature solid | β-Ca · BCC | Above the α→β transition and below melting | Measured |
| α→β transition | ≈721 K on heating | NIST-reviewed experimental recommendation | Evaluated |
|---|---|---|---|
| Melting point | 1115 K | RSC element reference | Evaluated |
| Boiling point | 1757 K | RSC element reference | Evaluated |
| Phase-path warning | Pressure shifts boundaries | Solid-state transition is separate from melting | Reviewed |
| Electrical behavior | Metallic conductor | Bulk calcium metal; exact values depend on condition | Measured |
|---|---|---|---|
| Materials distinction | Ca metal ≠ Ca²⁺ compounds | Limestone, gypsum and bone mineral are compound systems | Reviewed |
| Engineering values | Condition-dependent | Use material-specific data for design calculations | Reviewed |
| Common oxidation state | +2 | Characteristic Group 2 chemistry | Evaluated |
|---|---|---|---|
| Common simple ion | Ca²⁺ | Loss of two 4s electrons | Evaluated |
| Representative minerals | Calcite / aragonite · gypsum · apatite | Examples of calcium-bearing compounds | Reviewed |
| ⁴⁰Ca | 96.941% | Stable · RSC displayed abundance | Evaluated |
|---|---|---|---|
| ⁴²Ca | 0.647% | Stable | Evaluated |
| ⁴³Ca | 0.135% | Stable | Evaluated |
| ⁴⁴Ca | 2.086% | Stable | Evaluated |
| ⁴⁶Ca / ⁴⁸Ca | 0.004% / 0.187% | Naturally occurring very low-abundance isotopes | Evaluated |
Calcium changes crystal structure before it melts
At approximately standard pressure, calcium has an α solid region below about 721 K and a β solid region from about 721 K to the 1115 K melting point. The liquid then persists to the 1757 K boiling reference.
The ≈721 K α/β boundary follows the NIST-reviewed experimental recommendation; melting and boiling use the RSC element reference. Pressure can shift phase boundaries.
From lime and limestone to elemental calcium
Lime chemistry came first
Calcium-rich limestone and lime were used long before the element was isolated.
Humphry Davy
Davy isolated calcium during the early era of electrochemical element discovery.
Name from calx
The name traces to the Latin word associated with lime.
Compounds dominate
Construction, agriculture, water chemistry and biology all depend heavily on calcium compounds.
How calcium metal is produced
Industrial calcium metal can be made by electrochemical or metallurgical routes from calcium compounds. This is a process overview, not a laboratory procedure.
Start with calcium minerals
Natural feedstocks contain calcium in stable compounds.
Prepare a suitable calcium salt
Purification and conversion create a feed appropriate to the chosen industrial route.
Reduce Ca²⁺
Electrical or metallurgical energy converts calcium ions to metal.
Protect the reactive metal
The product is handled to limit uncontrolled reaction with air or moisture.
Why calcium matters
Bones + teeth
Calcium-phosphate mineral phases provide structural strength in vertebrate hard tissues.
Cement + lime
Calcium compounds are fundamental to cement, mortar and many construction materials.
Agriculture
Calcium compounds are used to manage soils and provide plant nutrients.
Cell signaling
Controlled Ca²⁺ concentrations act as signals in cells, muscles and nerves.
Metallurgy
Calcium metal is used in specialized reducing, deoxidizing and alloying roles.
Water chemistry
Dissolved Ca²⁺ contributes to water hardness and carbonate equilibria.
Six naturally occurring stable calcium isotopes
Abundances shown from the RSC element reference; values are rounded as displayed there.
Three-question calcium check
What simple ion does calcium commonly form?
Which isotope dominates natural calcium?
Why is calcium usually found in compounds?
Calcium questions: quick answer first, then the mechanism
Why does calcium usually form Ca²⁺?
Short answer: Two outer 4s electrons can be removed to expose an argon-like core.
The first two ionizations remove the outer-shell pair. A third would break into the closed-shell core and is much more energetically costly.
Why are bones and limestone stable if calcium metal is reactive?
Short answer: They contain calcium already bound as Ca²⁺ in stable compounds.
Elemental reactivity and compound stability are different questions. In carbonates and phosphates, electrostatic attraction and extended solid structures stabilize the ionic material.
Is the 40.078 atomic mass the mass number of one calcium atom?
Short answer: No.
40.078 is a relative atomic-mass value reflecting natural isotopic composition. Individual isotopes have integer mass numbers such as 40 or 44.
Scientific sources for Calcium
Questions to ask next about Calcium
A good element lesson should lead to the next useful question, not end after a list of facts.
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