Here's why:

* Electron Configuration: Fluorine's electron configuration is 1s² 2s² 2p⁵.

* Valence Shell: The outermost shell (in this case, the second shell) is considered the valence shell.

* Valence Electrons: The electrons in the valence shell are the valence electrons, which are involved in chemical bonding. In fluorine, there are 2 electrons in the 2s subshell and 5 electrons in the 2p subshell, totaling 7 valence electrons.