Here's why:

* Atomic Number: Fluorine's atomic number is 9, meaning it has 9 protons and 9 electrons in a neutral atom.

* Electron Configuration: The electron configuration of fluorine is 1s² 2s² 2p⁵.

* Valence Electrons: Valence electrons are the electrons in the outermost energy level (shell). In fluorine's case, the outermost shell is the second shell (2s and 2p orbitals). There are 2 electrons in the 2s orbital and 5 electrons in the 2p orbital, making a total of 7 valence electrons.