Question

Oxygen has 1st electrongainenthalpy _144 and 2nd is +780 why

Answer 1

Answer: Yes

Explanation: Oxygen has a valency of 2. That means it needs Two more electrons to completely fill its orbitals/shells. For the first electron, electron gain enthalpy is negative and second electron gain enthalpy is positive because 1. after getting the second electron, it will attain stable configuration

2. When the second electron will come, it will feel strong electrostatic repulsion due to which for getting the electron inside, we need to supply energy

Hope it helps!!!!

You can also study the case of Magnesium and Beryllium Ionisation Enthalpy for a better view.