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why does hydration entalpies of alkali metals decrease with increase in ionic size?

why does hydration entalpies of alkali metals decrease with increase in ionic size?

Grade:11

1 Answers

Arun
25750 Points
6 years ago

The size of the hydration enthalpy is governed by the amount of attraction between the ions and the water molecules.

  • The attractions are stronger the smaller the ion. For example, hydration enthalpies fall as you go down a group in the Periodic Table. The small lithium ion has by far the highest hydration enthalpy in Group1, and the small fluoride ion has by far the highest hydration enthalpy in Group 7. In both groups, hydration enthalpy falls as the ions get bigger.
  • The attractions are stronger the more highly charged the ion. For example, the hydration enthalpies of Group 2 ions (like Mg2+) are much higher than those of Group 1 ions (like Na+).

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