Quick Facts
| Property | Value |
|---|---|
| Symbol | Ca |
| Atomic Number | 20 |
| Atomic Mass | 40.078 u |
| Category | Alkaline Earth Metal |
| Period | 4 |
| Group | 2 |
| Block | s |
| Electron Configuration | [Ar] 4s² |
Physical Properties
| Property | Value |
|---|---|
| State at 20°C | Solid |
| Density | 1.55 g/cm³ |
| Melting Point | 842°C (1115 K) |
| Boiling Point | 1484°C (1757 K) |
| Appearance | Silvery-gray metal |
Atomic Properties
| Property | Value |
|---|---|
| Electron Configuration | [Ar] 4s² |
| Electronegativity | 1.00 (Pauling scale) |
| First Ionization Energy | 589.8 kJ/mol |
| Atomic Radius | 197 pm |
| Covalent Radius | 176 pm |
| Van der Waals Radius | 231 pm |
History and Discovery
Discovered by: Humphry Davy Year of Discovery: 1808 Location: London, England
Etymology
The name "calcium" comes from the Latin "calx" meaning "lime." Lime (calcium oxide) has been used since ancient times.
Discovery Story
Calcium compounds like lime (CaO) and gypsum (CaSO₄) have been known since antiquity. Humphry Davy isolated calcium metal in 1808 by electrolyzing a mixture of lime and mercuric oxide. He used similar techniques to those he employed for sodium and potassium.
Isotopes
| Isotope | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|
| ⁴⁰Ca | 96.94% | Stable | - |
| ⁴²Ca | 0.647% | Stable | - |
| ⁴³Ca | 0.135% | Stable | - |
| ⁴⁴Ca | 2.09% | Stable | - |
| ⁴⁶Ca | 0.004% | Stable | - |
| ⁴⁸Ca | 0.187% | 6.4 × 10¹⁹ years | β⁻β⁻ |
Occurrence
Natural Abundance
Calcium is the fifth most abundant element in Earth's crust (about 4.1%). It never occurs free in nature. Major sources include limestone (CaCO₃), gypsum (CaSO₄), and fluorite (CaF₂). Calcium is also abundant in seawater.
Extraction and Production
- Electrolysis: Of molten calcium chloride (Dow process)
- Aluminothermic Reduction: Of lime with aluminum
- Sources: Limestone quarrying
- Global production: about 25,000 tons of metal annually
Applications and Uses
Construction Materials
- Cement and concrete (calcium silicates)
- Mortar and plaster (calcium hydroxide)
- Limestone and marble for building
- Gypsum for drywall
Industrial Applications
- Steel production (desulfurization)
- Reducing agent for other metals
- Lead-calcium alloys for batteries
- Aluminum production (flux)
Chemical Applications
- Calcium carbide for acetylene production
- Bleaching powder (calcium hypochlorite)
- Water treatment
- Paper manufacturing
Other Uses
- Dietary supplements
- Antacids (calcium carbonate)
- Pyrotechnics (orange flame)
Biological Role
Calcium is essential for life. It is the most abundant metal in the human body, vital for bones, teeth, muscle function, and cell signaling.
In the Human Body
- About 1.5% of body mass (1 kg in adult)
- 99% in bones and teeth as hydroxyapatite
- Essential for muscle contraction
- Required for blood clotting
- Crucial for nerve transmission
- Daily requirement: 1,000-1,200 mg
Dietary Sources
Dairy products, leafy greens, fortified foods, fish with bones, and almonds are rich in calcium.
Safety and Hazards
Toxicity
Calcium compounds are generally safe. Excess intake can cause hypercalcemia. Metallic calcium reacts with moisture and can cause burns.
Handling Precautions
- Metal reacts with water (less violently than alkali metals)
- Can ignite in air when finely divided
- Store in dry conditions
- Quickite (CaO) is caustic and exothermic with water
Environmental Impact
Calcium is naturally abundant and environmentally benign. Limestone quarrying has local environmental impacts.
Interesting Facts
- The average adult body contains about 1 kilogram of calcium
- Calcium is the fifth most abundant element in the human body by mass
- Coral reefs, seashells, and eggshells are made of calcium carbonate
- Roman concrete used lime (calcium oxide) and lasted for millennia
- Calcium ions are crucial signaling molecules in nearly every cell type