Periodic Trends and Chemical Reactivity | Class XI

 

  • As we have seen, the ionization enthalpy of the extreme left element in a period is the least and the electron gain enthalpy of the element on the extreme right is the highest negative (excluding noble gases). This results in high chemical reactivity at the two extremes and the lowest in the centre.
  • Thus, Alkali metals (at extreme left) has maximum tendency to form cation (by loss of an electron) and halogens (at extreme right) has maximum tendency to form anion (by gain of an electron).
  • Thus metallic character is maximum at the left and non-metallic character is maximum at the right within a period.
  • The oxides formed by the elements at the left of the periodic table are basic (e.g., Na2O) while oxides formed by the elements at the right of the periodic table are acidic (e.g., Cl2O7). However, oxides of elements in the centre are either amphoteric (e.g., Al2O3, Ab2O3) or neutral (e.g., CO, NO, N2O).
  • In transition metals, change in atomic radii is much smaller than representative elements. Their ionization enthalpies are between s-and p-block elements. Therefore, they are less electropositive than group 1 and 2 metals.
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