Why is boron and beryllium an exception to the octet rule

Explanation:

Beryllium especially, but Boron as well both exhibit metallic characteristics.

The outside ring of Beryllium contains 2 electrons. It would have to take on 6 electrons to have a ring of 8. The same statement can be made about Boron (except that it would need 5 electrons to make 8). It is easier for the atom to give up 2 or 3 than than to take on 5 or 6. It would not be easy to have a 5 or 6 minus charge on it.

the electrical  conductivity  of asolution  of an electrolyte is measured by determining the resistance of thesolution  between two flat or cylindrical electrodes separated by a fixed distance.