Question

my reacher told me that there were only 8 electrons which can be fitted in m shell of an atom but at the same time she told us the formula of 2n2 which gives the number of electrons 18 in the m shell.... why ??

Answer 1

The M shell only holds eight electrons. The M shell can actually hold up to 18 electrons as you move to higher atomic numbers. The maximum number of electrons you will find in any shell is 32.

Answer 2

Hi.

This concept is given by the Bohr-Bury Scheme.

According to it,

1. Electrons revolve around the nucleus n special discrete orbits called energy levels or shells.
2. While travelling in them, they can neither loose energy or gain energy. Energy is lost or gained only when the electrons jump from 1 shell to another.
3. The maximum no. of electrons that can be accomodated in a shell is given by the formula 2n², where n is the orbit number. This way, the no. of maximum electrons in the first shell = 2*(1)² = 2*1 = 2 electrons; in the second shell = 2*(2)² = 2*4 = 8 electrons; in the third shell = 2*(3)² = 2*9 = 18 electrons.
4. The maximum no. of electrons that can be accomodated in the ;ast shell of any atom is 8, even if the previous rule is violated.

Eg: EC of Ne = 2, 8; of Na = 2, 8, 1 and not 2, 9 because of rule number 4.

But, the third shell can have more than 8 electrons if it is not the outermost shell.

Eg: EC of Zn = 2, 8, 18, 2.

Hope it helps.!