What does the octet rule state that explains why atoms bond

The octet rule is a chemical rule of thumb that reflects observation that atoms of main-group elements tend to combine in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas. The rule is especially applicable to carbon, nitrogen, oxygen, and the halogens, but also to metals such as sodium or magnesium.

The valence electrons can be counted using a Lewis electron dot diagram as shown at the right for carbon dioxide. The electrons shared by the two atoms in a covalent bond are counted twice, once for each atom. In carbon dioxide each oxygen shares four electrons with the central carbon, two (shown in red) from the oxygen itself and two (shown in black) from the carbon. All four of these electrons are counted in both the carbon octet and the oxygen octet.

Atoms bond to attain the stable electronic configuration.                

Explanation:

According to the octet rule, the chemical elements tend to form chemical bonds in order to attain the stable noble gas electronic configuration. The chemical elements having a stable outer electronic configuration of s²p⁶, are said to have a closed shell, in which eight electrons are present in their outermost shell of the atom.

Therefore, the chemical elements tend to gain or lose or share electrons in order to attain the stable electronic configuration. Thus satisfying the octet rule.