Atomic Theory

Having different charges, and therefore an attractive force for each other, Na+ and Cl- in a sodium chloride crystal, arrange themselves into a rigid solid, ionic crystal. The form used to describe this crystal is Na+Cl-, meaning that the Na+  and   Cl- ions arrange themselves in equal numbers.    

Sodium chloride crystallizes in the form of a Face-Centered cube a diagram of which is shown below:

For one face, that marked A B C D in the above diagram, the ends of the cube are ALL occupied by Na+ ions. Cl- ions are then spaced between them. For the other face, marked E F G H in the diagram above, the ends of the cube are ALL occupied by Cl- ions. Na+ ions are then spaced out between them.

The attractions between Na+ and Cl- ions are great and there are only slight vibrations between the ionic bonds joining the differently charged ions.

Note: The name of an ionic compound always consists of the name of the cation placed at the beginning of the name, followed by the name of the anion.

Consider an atom of magnesium which has an atomic number of 12 and an electronic configuration of  (2 8 2). This element is found in group 2 of the Periodic Table. In order to become stable this has to lose its two outermost electrons.

Magnesium atom                                                                           Magnesium ion

Xx                                                       Mg  – 2e-        Mg2+