Question

why first electron gain enthalpy is -ve ans second electron gain enthalpy is +ve explain.

Answer 1

First electron enthalpy is negative because the energy is released when an electron is added to an atom. This converts the atom into a monovalent anion. Now, if another electron is added to this anion, they'll repel each other because both of them have negative charge and some energy will be absorbed. Therefore, second and further successive electron gain enthalpy are positive (because the energy is absorbed.)

Answer 2

Answer:

When the first electron is added to the gaseous atom , it forms a uni - negative ion and enthalpy . ... Thus , when an electron is added to O atom , the energy is released , so the first electron gain enthalpy is negative .