An atom of fluorine has seven electrons in its outermost layer. Fluorine is the most electronegative and, therefore, the most reactive element on the periodic table. Fluorine readily grabs an electron from another atom to achieve a more stable configuration.
Fluorine is so reactive that it reacts with all the other elements and can never be found in its elemental form in nature. Fluorine is the most electronegative element on the periodic table, meaning that it has a great affinity for electrons. According to the octet rule, most atoms strive to have eight electrons in their outermost energy level to become more stable. Because fluorine already has seven valence electrons, it desperately wants to gain just one more to fill its outermost energy level.