Periodic Table
20
Ca
40.078
Calcium
Alkaline EarthBrick-red flame; bones & teeth; lime chemistry (CaO, Ca(OH)₂).
Electronic Configuration
[Ar] 4s²or1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
Electron shells
2e⁻n=1
8e⁻n=2
8e⁻n=3
2e⁻n=4
Properties
Atomic number
20
Atomic mass
40.078 u
Category
Alkaline Earth
Block / Group / Period
s · 2 · 4
Valence electrons
2
Oxidation states
+2
Electronegativity
1
Atomic radius
194 pm
Ionization energy
590 kJ/mol
Electron affinity
2 kJ/mol
Melting point
1115 K / 842 °C
Boiling point
1757 K / 1484 °C
Density
1.55 g/cm³
State at 25 °C
solid
JEE / NEET notes
- Lime water Ca(OH)₂ + CO₂ → milky CaCO₃ (CO₂ test).
- Plaster of Paris: CaSO₄·½H₂O; gypsum heated to 120°C.
- Bleaching powder Ca(OCl)Cl.
Flame test
Brick red
Ores & extraction
Ores: Limestone (CaCO₃), Gypsum (CaSO₄·2H₂O), Fluorspar (CaF₂)
Uses
Cement & lime · Plaster of Paris · Bleaching powder · Steel making
Important compounds
CaOCa(OH)₂CaCO₃CaSO₄·½H₂O
Personal Notes
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