Question #975ae

Ionic compounds are formed between a positive ion and a negative ion. These ions have opposite charges, creating an electrochemical attraction similar to the opposite ends of magnets having an attraction.

There are two types of ionic compounds. The first is created when a positive metal cation is attracted to a negative non-metal anion.
When the charges of these ions are equal and opposite the atoms will bond

A sodium cation #Na^(+1)# is attracted to a chlorine anion #Cl^(-1)#
to form a NaCl salt molecule of sodium chloride.

In the case of a calcium cation #Ca^(+2)# the attraction to chlorine requires two chlorine anions #Cl^(-1)# in order for the charges to be equal. This makes a #CaCl_2# calcium chloride salt.

The other form of ionic bond takes place between a positive metal cation and a polyatomic ion composed of more than one type of atom.

Potassium #K^(+1)# will be attracted to the nitrate polyatomic anion #NO_3^(-1)# in a one to one ratio of #KNO_3# potassium nitrate.

Calcium #Ca^(+2)# will have an attraction to phosphate #PO_4^(-3)# but only if the charges are equal and opposite. Therefore, there will be three #Ca^(+2)# cations and two #PO_4^(-3)# anions to make a compound of #Ca_3(PO_4)_2# calcium phosphate.

I hope this was helpful.
SMARTERTEACHER