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Compare Chlorine vs Astatine

Comparing Chlorine (Cl) and Astatine (At). Atomic numbers 17 and 85 with atomic masses 35.446 u and 210 u, classified as nonmetal and metalloid. Below: a side-by-side comparison of their physical, atomic, electron-configuration and historical properties, including density, melting and boiling points, ionization energies, oxidation states and discovery history.

vs
Cl
Chlorine
#17
At
Astatine
#85

Periodic properties of the elements

ChlorineAstatine
SymbolClAt
Atomic number1785
Group1717
Period36
Blockpp
Element categoryNonmetalMetalloid

Physical properties

ChlorineAstatine
Phase at STPGasSolid
Density3.2 g/cm36.35 g/cm3
Atomic weight35.446 u210 u
Melting point171.6 K
-101.55 °C
-150.79 °F		575 K
301.85 °C
575.33 °F
Boiling point239.11 K
-34.04 °C
-29.272 °F		610 K
336.85 °C
638.33 °F

Atomic properties

ChlorineAstatine
Electronegativity (Pauling Scale)3.162.2
Electron affinity348.575 kJ/mol233 kJ/mol
Oxidation states−1, +1, +2, +3, +4, +5, +6, +7
(a strongly acidic oxide)		−1, +1, +3, +5, +7
()
Ionization energies
  1. 1251.2 kJ/mol
  2. 2298 kJ/mol
  3. 3822 kJ/mol
  4. 5158.6 kJ/mol
  5. 6542 kJ/mol
  6. 9362 kJ/mol
  7. 11018 kJ/mol
  8. 33604 kJ/mol
  9. 38600 kJ/mol
  10. 43961 kJ/mol
  11. 51068 kJ/mol
  12. 57119 kJ/mol
  13. 63363 kJ/mol
  14. 72341 kJ/mol
  15. 78095 kJ/mol
  16. 352994 kJ/mol
  17. 380760 kJ/mol
  1. 899.003 kJ/mol

Electron configuration

ChlorineAstatine
Shorthand configuration[Ne] 3s2 3p5 [Xe] 4f14 5d10 6s2 6p5
Full configuration1s2 2s2 2p6 3s2 3p5 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p5
Electrons per shell2, 8, 72, 8, 18, 32, 18, 7

History

ChlorineAstatine
DiscoveryCarl Wilhelm Scheele (1774)Dale R. Corson, Kenneth Ross MacKenzie, Emilio Segrè (1940)
First isolationCarl Wilhelm Scheele (1774)
Named bySir Humphry Davy (1810)
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