Class 12 Chemistry P Block Elements Physical properties of group 17

Physical properties of group 17

  1. 1. Electronic configuration-The general electronic configuration for this group is ns2np5
  • Fluorine (F) [He]2s2,2p5
  • Chlorine (Cl) [Ne]3s2,3p5
  • Bromine(Br)[Ar]3d104s24p5
  • Iodine (I)[Kr]4d10,5s2,5p4
  • Astatine (At) [Xe]4f14,5d10,6s2,6p4
  1. Atomic size: It increases down the group as every time a new shell is added as we move down. If we compare size of group 17 elements with group 16 then we see that group 17 is smaller due to increased nuclear charge.
  2. Ionization energy: If we compare ionization energy of group 17 and group 16 we see that group 17 has higher energy than group 16 because of smaller size of group 17 elements.


  1. Electron gain enthalpy:
  • Along period it is more negative because of attraction towards electron as of increased nuclear charge.
  • Down the group electron gain enthalpy keeps on becoming less negative because nuclear charge decreases and size.
  • So, the group 17 has highest electron gain enthalpy due to smallest size in periodic table.
  • Please note that: Fluorine has less electron gain enthalpy than chlorine because due to small size of oxygen the incoming electron suffers repulsion therefore, electron gain enthalpy is less negative as compared to chlorine.
  1. Electro negativity: Group 17 elements are more electro negative than group 16 because of small size of group 17 elements. This group has highest electro negativity in whole periodic table.

Fluorine is most electronegative in periodic table. Down the group electronegativity decreases as the size increases.


  1. Melting point and boiling points: It increases down the group as size and mass increases the Vander wall force also increases therefore melting and boiling point increases.
  2. 7. Color: All halogens are colored like:

Fluorine: Dull yellow in color.

Chlorine: Greenish yellow.

Bromine: Reddish brown.

Iodine: Violet.

  1. Oxidation states: They show variable oxidation states like:

Fluorine: -1

Chlorine: -1, +1, +3, +7

Bromine : -1, +1, +3, +5, +7

Iodine:  -1, +1, +3, +5, +7

  • Higher oxidation states of halogens are used when they are combining with small size highly electronegative ions.
  • All halogens are very reactive and reactivity decreases down the group.
  • All act as Lewis acids as they accept electron.
  • Fluorine is the strong oxidizing agent among all.

Anomalous behavior of Fluorine:

  • Smallest size.
  • Highest electronegativity.
  • No vacant d orbital.

Low F-F bond dissociation energy.

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