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20 Ca Calcium 40.078

Alkaline-earth metal

Calcium 钙

[Ar] 4s²

  • Period 4
  • Group 2
  • Block s
  • Solid

Electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s²

Orbital diagram (valence)

4s ↑↓
Electrons per shell
2, 8, 8, 2
Unpaired electrons
0
Zeff (Slater)
2.85

Properties

Atomic weight
40.078
Electronegativity (Pauling)
1
First ionization energy
589.8 kJ/mol
Electron affinity
no data
Covalent radius
176 pm
van der Waals radius
231 pm
Melting point
1115 K
Boiling point
1757 K
Density
1.54 g/cm³
Melting / boiling point
841.9 °C / 1483.8 °C
Common oxidation states
+2
Discovered
Known since antiquity

Natural isotopes

Mass number AAbundance
40Ca96.94 %
42Ca0.6470 %
43Ca0.1350 %
44Ca2.09 %
46Ca0.004 %

Isotope masses: AME2020; abundances: IUPAC/CIAAW representative values.

Emission spectrum

Calcium flame · brick red

Explore in the spectroscope lab

Successive ionization energies

1: 6.11 eV2: 11.87 eV3: 50.91 eV4: 67.27 eV5: 84.34 eV6: 108.78 eV7: 127.21 eV8: 147.24 eV9: 188.54 eV10: 211.28 eV11: 591.60 eV12: 658.20 eV13: 728.60 eV14: 817.20 eV15: 894.00 eV16: 973.70 eV17: 1086.80 eV18: 1157.73 eV19: 5128.86 eV20: 5469.86 eV135791113151719n-th electron removed101001000Ionization energy / eV (log)

The big jumps appear where core electrons start to be removed. Ionization energies from the NIST Atomic Spectra Database.

Calcium in the course

The lessons that discuss this element most (ranked by mentions).

Lab experiments with Calcium

Standard reduction potentials

CaX2+(aq)+2 eX−→Ca(s)\ce{Ca^2+(aq)} + \ce{2e-} \mathrel{\ce{->}} \ce{Ca(s)}−2.868 V
All potentials

Crystal structures

  • CaFX2\ce{CaF2} Fluorite lattice parameter a = 546.3 pm
View in the crystal atlas

Periodic trend

H: 1312 kJ/molHe: 2372 kJ/molLi: 520.2 kJ/molBe: 899.5 kJ/molB: 800.6 kJ/molC: 1086 kJ/molN: 1402 kJ/molO: 1314 kJ/molF: 1681 kJ/molNe: 2081 kJ/molNa: 495.8 kJ/molMg: 737.7 kJ/molAl: 577.6 kJ/molSi: 786.5 kJ/molP: 1012 kJ/molS: 999.6 kJ/molCl: 1251 kJ/molAr: 1521 kJ/molK: 418.8 kJ/molCa: 589.8 kJ/molSc: 633 kJ/molTi: 658.8 kJ/molV: 650.9 kJ/molCr: 652.9 kJ/molMn: 717.3 kJ/molFe: 762.4 kJ/molCo: 760.4 kJ/molNi: 737.1 kJ/molCu: 745.4 kJ/molZn: 906.4 kJ/molGa: 578.8 kJ/molGe: 762.2 kJ/molAs: 947 kJ/molSe: 940.9 kJ/molBr: 1140 kJ/molKr: 1351 kJ/molRb: 403 kJ/molSr: 549.5 kJ/molY: 599.8 kJ/molZr: 640.1 kJ/molNb: 652.1 kJ/molMo: 684.3 kJ/molTc: 702.4 kJ/molRu: 710.2 kJ/molRh: 719.7 kJ/molPd: 804.4 kJ/molAg: 731 kJ/molCd: 867.8 kJ/molIn: 558.3 kJ/molSn: 708.6 kJ/molSb: 833.6 kJ/molTe: 869.3 kJ/molI: 1008 kJ/molXe: 1170 kJ/molCs: 375.7 kJ/molBa: 502.9 kJ/mol 0510152025303540455055Atomic number Z05001000150020002500First ionization energy / kJ/mol

Group 2

Data: PubChem periodic table (public domain); atomic weights are IUPAC abridged standard values; covalent radii from Cordero et al. (2008).