Sodium has an electronic configuration of 2,8,1. In order to have a full last shell, it needs to either gain 7 electrons or lose 1 electron. The latter is much easier and is what happens. Sodium looses an electron and becomes positively charged ion, but reaches a stable electronic configuration.$^0$
Chlorine has an electronic configuration of 2,8,7. In order for it to have a full last shell, it needs to either loose 7 electrons or gain 1. The latter is easier and is what happens. Chlorine gains an electron and becomes a negatively charged ion, but it reaches a stable electronic configuration.$^0$
In the previous section, I mentioned that Sodium forms a positive ion and Chlorine forms a negative ion. An ion is an atom that either gains or looses and electron. An ion is a charged particle that has an unequal number of electrons and protons.$^0$
We know that Sodium forms an ion with a charge of +1 and Chlorine forms an ion with a charge of -1. When Sodium and Chlorine react, Sodium gives an electron to Chlorine. This makes them oppositely charged ions, and thus they attract each other. This force of attraction is strong. Because it is the attraction between two ions, it is called as an ionic bond.$^0$
However, this is not in isolation. There are more than one pair of Chlorine and Sodium being reacted. Because they are bonded through positive-negative attraction, the attraction is non-directional. This results in a lattice structure of alternating Sodium and Chlorine atoms. This lattice grows and is called as giant, as it contains a large number of ions.$^0$
In order for an ionic bond to be formed, it needs to be between a metal and a non-metal. For example, Magnesium and Oxygen($\text{MgO}$) or Magnesium and Chlorine($\text{MgCl}_2$). Both have similar properties to that outlined for Sodium Chloride.$^0$
Naming an ionic compound is easy. First comes the positive ion and then the negative ion with the end -ide. For example, Sodium forms a positive ion and Chlorine forms a negative ion. So the name is Sodium Chloride. Another example is Magnesium forms a positive ion, and oxygen forms a negative ion. So the name is Magnesium Oxide.$^0$
In order to find the formula from the name, you first write down each of the elements. Then you write down the charge of the ion. As the ionic compound should be neutral, take the LCM of the charges, and write it as a formula.$^0$
Example Lithium Fluoride The ions are $\text{Li}^+$ and $\text{F}^-$ The LCM of the charges are 1, so the formula is $\text{LiF}$
Ionic compounds have a high melting an boiling point. This is due to the high strength of the bonds, as such it takes a lot of energy to break up the bonds.$^0$
Ionic compounds are usually soluble in water. Water is usually able to separate the ions.$^0$
Ionic compounds conducts electricity while either melted or dissolved. When solid, the ions are not free to move.$^0$