Although the M shell can hold 18 electrons, why does the third period …

Question

Although the M shell can hold 18 electrons, why does the third period contain only eight elements?

Accepted Answer

D. Because of the law of electron octet

1. The M shell's full capacity by $2n^2$ is 18 electrons.
2. Yet the third period stops at eight elements.
3. This is due to the law of electron octet governing the early periods.
4. Rule out B: the M-shell capacity is 18, not 8.
5. Rule out A: third-period atoms use the K, L and M shells.
_Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 2 "Periodic Classification of Elements", p.33_

Answer

Because the third period uses only the K shell

Answer

Because the M shell holds only eight electrons

Answer

Because only eight elements were discovered