What are some examples of ionic formulas?

1 Answer
Jul 11, 2014

Strontium Fluoride is an Ionic compound , with formula Sr F_2.

Let us see how we got the answer; Look at the electronic arrangement of Sr and F atom.

Sr ( Z= 38) has electrons with following electronic configuration. 1s^22s^22p^63s^23p^64s^23d^104p^65s^2

It loses two electron in its 5s subshell to achieve stability and forms ion Sr^(2+).

Sr^(2+) 1s^22s^22p^63s^23p^64s^23d^104p^6

F ( Z=9) on the other hand has nine electrons and wants to gain one more electron to achieve stable noble gas configuration.Fluorine atom on gaining one electron forms negative fluoride ion, F^- ion.

F( Z=9) = 1s^22s^22p^5

F^- = 1s^22s^22p^6

Two Fluorine atoms gains one electrons each ( total of two) from one Sr atoms, each Sr atom loses two electrons ( one each) to two chlorine atoms , in this process each Sr atom becomes Sr^(2+) ion and each fluorine atom after gaining one electron becomes F^- ion.

so in all we have one Sr^(2+) ions and two fluoride F^- ions.
so the formula becomes SrF_2.

Look at the electronic arrangement of Ca and N atom.

Ca ( Z= 20) has 20 electrons with following electronic configuration. 1s^22s^22p^63s^23p^64s^2.

It loses two electron in its 4s subshell to achieve stability and forms ion Ca^(2+).

Ca^(2+) = 1s^22s^22p^63s^23p^6

N ( Z=7) on the other hand has seven electrons and wants to gain three electrons to achieve stable noble gas configuration.Nitrogen atom on gaining three electrons forms negative nitride ion, N^-3 ion.

N ( Z=7) = 1s^22s^22p^3

N^-3 = 1s^22s^22p^6

Two Nitrogen atoms gains three electrons each ( total of six) from three Ca atoms, each Ca atom loses two electrons (total of six) to two Nitrogen atom , in this process each Ca atom becomes Ca^(2+) ion and nitrogen atom after gaining three electrons becomes N^-3 ion.enter image source here

so in all we have three Ca^(2+) ions and two nitride N^-3 ions.
so the formula becomes Ca_3 N_2.