Question

How can I write the formula of strontium fluoride?

Answer 1

Hint:Molecular formula or Ionic formulas are formed by the combination of anion and cation. In an ionic compound one cation is surrounded by various numbers of anions, similarly one anion is surrounded by various numbers of cations.

Complete step by step answer:
Ionic compounds are compounds which are formed by the combination of cation and anion. In between anion and cation an electrostatic force of attraction is present between cation and anion which is one of the strongest forces among the primary forces.
Ionic compounds are formed by transfer of electrons between highly electropositive atoms and highly electronegative atoms. Metals are highly electropositive atoms which readily lose electrons and form a cation while non metals are highly electronegative elements which readily gain electrons and form an anion.
Due to the presence of electrostatic force of attraction between cation and anion, melting and boiling point of ionic compounds is very high. In solid state they are bad conductors of electricity while in aqueous state they are good conductors of electricity.
Let us find the formula of strontium fluoride:
By criss cross valency method we can find the formula of strontium fluoride, In this method by cross multiplying the valency of ions we can neutralize the charge of an ion as well as we can find the formula of an ionic compound.
Strontium belongs to alkaline earth metal family and it contains two valence electrons which it can readily loses to form $+2$ oxidation state while fluorine belongs to halogen family which requires only one electron to complete its octet and show $-1$ oxidation state.
\[\,\,Sr\,\,\,\,\,\,\,\,\,\,\,\,\,F\]
      \[\searrow \swarrow \]
\[Ch\arg e\,\,\,\,\,\,\,\,\,+2\,\,\,\,\,\,\,\,\,\,\,\,\,-1\]
By cross multiplying method we can write the formula of strontium fluoride i.e., ${{\operatorname{SrF}}_{2}}$
Final answer:
The formula of strontium fluoride is ${{\operatorname{SrF}}_{2}}.$

Note:
Apart from ionic bonds in between atoms covalent bond also exists which is formed by the sharing of electrons between two electronegative atoms or between those two elements which has less difference in electronegativity.