CBSE Class 11-science Answered

An orbital cannot have more than two electrons. This is because no two electrons can have the all the values of the four quantum num bers same.

It can have the values of three quantum numbers same but not all four.

Example: Let us consider 1s orbital.

This electron will have the following values of quantum numbers:

n =1

l = 0

m_l = 0

m_s =+1/2

Now, if a second electron occupies the orbital with the opposite spin:

For the second electron, the values of quantum numbers will be:

n =1

l = 0

m_l = 0

m_s = -1/2

Here, the values of three quantum numbers are same bu the fourth one is different.

Now, two electrons are occupied.

If I try to accomodate a third electron here, it will either have a clockwise spin or anticlockwise spin.So, it will have the values of all four quantum numbers same as either that of the first electron or the second electron wihic will violate the principle. Hence, a moximum of only two electrons can be accomodated in any orbital.