Question

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.

Answer 1

b) repulsion of electrons increase. they need less energy to leave

Answer 2

a) In general, the electronegativity increases over a period from “left to right” (e.g., Li to F in the second period). It is because of decrease the atomic size and increases “effective nuclear charge”. As a result of “increase” effective nuclear charge, then nuclear attraction power increases on the outer shell electrons along period. Therefore, increases the electronegativity.

b) When the enthalpy of ionization moves down in a group gradually decreases. Decreasing the ionization enthalpy in a group can be explained by the following factors. When move down in a group

i) Increase the nuclear charge

ii) Increasing the atomic size

iii) Increase shielding effect

Increase in all these effects least increase nuclear attractions. As a result, when we move “down” the group, the electron becomes less which decreases the strength in the nucleus. Therefore, ionization enthalpies in one group are gradually decreasing.