11th Class Chemistry Classification of Elements and Periodicity in Properties

  • question_answer 89)   Explain the following : (a) Electronegativity of elements increase on moving from left to right in the periodic table. (b) Ionisation enthalpy decrease in a group from top to bottom.


      (a) Electronegativity of elements increases on moving from left to right in the periodic table as non-metallic character increases, the tendency to accept electron increases and the atomic radius decreases, i.e., effective nuclear charge increases. (b) In a normal group, the ionisation enthalpy decreases from top to bottom. On moving the group, the atomic size increases gradually due to addition of one new principal energy shell at each succeeding element. On account of this, the force of attraction towards the outermost electron decreases and hence the ionisation enthalpy value decreases.

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