Question

when naming a binary ionic compound how do you know what numbers to add? for example on BeF2 it is berylium fluoride but I dont unbwr stand where the 2 comes from on the end of F

Let's try naming these binary ionic compounds. BeF, Beryllium fluoride Lif Lithium fluoride • NaBr • MgS. Magnesium Bullde • CaBr Cacium bromide SrTe Strontium telluride K. Se Potassium selenide RbIᏒᎢ Rubidinum iodido Cao Calcium ondas CsCl Calum chloride AICI Aluminum chloride AC InN Indium nitrides

Answer 1

The formula of a compound is determined by the valency of combining elements.

Valency means the combining capacity of an element. This is the number of electrons an atom of the element loses, gains or shares to acquire stability, that is to acquire noble gas configuration.

The valencies of the combining elements are cross multiplied to find formula of the compound. This is done so that the total number of electrons lost by electropositive element is equal to total number of electrons gained by electronegative element .

For example, the compound sodium chloride, NaCl is formed by ions Na⁺ and Cl^- ions. The valency of Na⁺ is 1 and the valency of Cl^- is 1. On cross multiplying the valencies, we get the formula NaCl.

Similalry,BeF₂ is formed by ions Be²⁺ and F^- ions. The valency of Be²⁺ is 2 and valency of F^- is 1. On cross multiplying the valencies, we get the formula BeF₂.