question_answer 78)

  Among the elements B, Al, C and Si: (i) Which element has the highest first ionisation enthalpy? (ii) Which element has the most metallic character? Justify your answer in each case.

Answer:

  (i) Carbon has the highest first ionisation enthalpy among the elements B, Al, C and Si. The first ionisation enthalpy of C is more than B on account of higher nuclear charge. B and Al belong to the same group and B has higher value than Al as it is smaller in size. Similarly C and Si belong to the same group and C has higher value than Si as it is smaller in size. The order of first ionisation enthalpy among these elements is : Al < Si < B < C (ii) Aluminium is the most metallic element among the elements B, Al, C and Si. Metallic nature decreases in a period but increases in a group from top to bottom.