Valency of Fluorine in CaF2 (Calcium Fluoride) Explained

To determine the valency of Fluorine in this specific compound, let's look at the two elements:

• Calcium (Ca): Atomic number 20. It is an alkaline earth metal in Group 2. Its electron configuration is [Ar] 4s². It has 2 valence electrons and needs to lose them to become stable.
• Fluorine (F): Atomic number 9. It is a halogen in Group 17. Its electron configuration is [He] 2s² 2p⁵. It has 7 valence electrons and urgently needs 1 more electron to complete its octet.

Because Calcium needs to lose two electrons, and a single Fluorine atom can only accept one electron, a 1:1 ratio will not work.

Instead, one Calcium atom donates its two valence electrons to two separate Fluorine atoms (one electron to each).

• The Calcium atom becomes a Ca²⁺ ion.
• Each of the two Fluorine atoms gains one electron, becoming two F⁻ ions.

Because each individual Fluorine atom is only accepting exactly one electron to form the bond, the valency (combining capacity) of Fluorine in this compound is 1.

Fluorine's valency of 1 in CaF₂ is not an exception; it is the rule. As the most electronegative element on the periodic table, Fluorine virtually always exhibits a valency of 1 (an oxidation state of -1) in its compounds. It never shares its electrons to form positive oxidation states, unlike other halogens like chlorine or iodine, which can have variable valencies when bonded to oxygen.