* Valence Shell: The outermost electron shell of an atom.

* Fluorine: Has an atomic number of 9, meaning it has 9 protons and 9 electrons.

* Electron Configuration: Fluorine's electron configuration is 2, 7. This means it has 2 electrons in the first shell and 7 electrons in the second (valence) shell.

* Octet Rule: Atoms tend to gain, lose, or share electrons to achieve a full outer shell with 8 electrons (except for hydrogen and helium, which only need 2).

Since fluorine has 7 electrons in its valence shell, it can accommodate 1 more electron to achieve a stable octet.