# Which electron configuration represents an element with the highest first ionization energy?

##### 1 Answer
Jan 21, 2017

Helium wins in this category: $1 {s}^{2}$

#### Explanation:

Think of ionization energy as the separation between the energy of the electron in its ground state in the atom, and the same electron being removed from the atom - having its energy raised to zero.

This means that the electron in the lowest energy level within its atom would require the most energy to ionize. While both hydrogen and helium have a $1 s$ electron as the outermost electron, helium requires much more energy to ionize because of the double charge on its nucleus (compared to hydrogen).