Question

How do you determine if a pair of elements will most likely form an ionic compound?

Answer 1

Ionic compounds mean there is an ionic bond between two atoms. When the ionic bonds break there is the formation of ions having equal charge or having charge equal to the number of atoms. So, the opposite ions can make an ionic bond.

Complete answer:
Ionic compounds mean the bond between the atoms is ionic and when the bond breaks there is the formation of two types of ions, i.e., a cation and an anion. The cation will have the positive charge and the anion will have the negative charge.
For the formation of an ionic compound, one must be a metal and the other must be a non-metal. The metal will be mostly a cation and the non-metal will be mostly an anion.
For example, sodium chloride whose formula is $NaCl$ is an ionic compound because, in sodium chloride, sodium is the metal and chlorine is the non-metal. When the bond breaks the two ions formed are $N{{a}^{+}}$ and $C{{l}^{-}}$. Since both of them have the same valency, both the ions are equal in number.
$CaC{{l}_{2}}$ is also an ionic compound and its name is calcium chloride. Calcium is the metal and chlorine is the non-metal. When the bond breaks there is the formation of three ions, i.e., $C{{a}^{2+}}$ and two $C{{l}^{-}}$ ions. There are two chlorine atoms because the valency of the calcium is 2 and to balance the charge there are two chlorine atoms.

Note:
The ionic bond is a strong bond because when it breaks, the ions due to electrostatic forces will tend to come close to each other and will again try to form the bond. D-block elements can also form an ionic compound.