Wednesday, October 9, 2013

Periodic Trends Of Alkali Metals


  • Ionization Energy:
Alkali metals have low ionization energy.
                     The first ionization energies of alkali metals are relatively low and decreases on moving down the group.

Reason:
   Atomic radius gets increases on moving down the group. so the outermost electron gets farther away from the nucleus and therefore the first ionization energy decreases.
   The second ionization energy of the alkali metals are high. The second most loosely held electrons is part of a fully filled electron shell and is thus difficult to remove.

  • Electropositive Character:
Electropositive character increases go down the group.
                    M      →     M+      +     1e-
Reason:
     The first ionization energy of alkali metals decreases down the group, it is easier to remove the outermost electron from the atom and the participate in chemical reaction thus increasing the electropositivity down the group. The alkali metals are high electropositive that they emit electrons when irradiated with light.This effect is known as photoelectric effect. Due to this property Cs and K are used in photoelectric cells.
  • Melting And Boiling Point:
Alkali metals have low melting and boiling point.
Reason:
     The weak interatomic bonds are attributed to their large atomic radii and the presence of one valance electron. The atoms increases in size going down the group. The nuclei of the ions are move further away from the delocalised electrons and hence the metallic bond becomes weaker. Therefore the melting and boiling point decreases going down the group.
  • Density:
Alkali metals have high density.

Reason:
     The trends for the densities of the alkali metals depends on their atomic weight and atomic radii. The densities of the alkali metals increases moving down the group with an exception at potassium. Lithium has low density due to the low atomic weight of the atom.
  • Oxidation And Reduction:
Oxidation:
     Alkali metals have only one electron in their outermost valence shell. So they easily lose one electron in their outermost shell and form a stable configuration of the nearest inert gas. They are monovalent elements showing an oxidation state of +1.
Reduction:
     Alkali metals have low ionization energy, they easily lose their valence electron. Therefore these elements behaves as good reducing agents
  • Atomic And Ionic Radii
            Atomic and Ionic radii of alkali metals are increases on moving down the group. The ionic radii of the alkali metals are much smaller than their atomic radii.



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