* Highly reactive: Fluorine is the most reactive non-metal element. This is due to its high electronegativity and strong tendency to gain an electron to achieve a stable octet.

* 7 more electrons: Fluorine has 9 electrons (2 in the first shell and 7 in the second). To complete its outer shell and achieve a stable octet, it needs one more electron.

* Fewer protons than sodium: Fluorine has 9 protons, while sodium has 11 protons. This makes fluorine a smaller atom with a stronger pull on electrons.

Key Point: The number of protons defines an element. Elements in the same group (column) of the periodic table have similar chemical properties.