Question

which of the following is the ground - state electron configuration of the f⁻ ion?
a 1s² 2s²2p⁴
b 1s² 2s²2p⁵
c 1s² 2s²2p⁶
d 1s² 2s²2p⁶ 3s²3p⁶

Explanation:

Fluorine (F) has an atomic number of 9. The neutral F atom has 9 electrons with electron - configuration $1s^{2}2s^{2}2p^{5}$. The $F^{-}$ ion has gained one extra electron. So the total number of electrons in $F^{-}$ is 10. The electron - configuration of an atom or ion is written by filling the orbitals in order of increasing energy (1s before 2s, 2s before 2p etc.). After gaining an electron, the extra electron goes into the 2p orbital, making the electron - configuration of $F^{-}$ as $1s^{2}2s^{2}2p^{6}$.

Answer:

C. $1s^{2}2s^{2}2p^{6}$