Question

Question 2.31 How many electrons in an atom may have the following quantum numbers?

(a) n = 4, ms = -1/2

(b) n = 3, l = 0

Class XI Structure of Atom Page 67

Answer 1

The total number of electrons in n is given by 2n2
n=4, Number of electrons = 2×42 = 32

Half of 32 electrons will have spin quantum number ms = –½ i.e. 16 electrons

(ii) n=3 and l=0 means it is 3s orbital which can have only 2 electrons.

Answer 2

concept :
total number of electrons in n shell = 2n²
total number of electrons in a orbitals = 2


(a) n = 4 , ms = -1/2
total number of electrons in n = 4 shell = 2(4)²
= 2 × 16 = 32
but we know, there are two spin quantum number positive spin and negative spin .
hence, half of electrons are positive spin and half of electrons are negative spin .

so, 16 electrons have ms = -1/2


(b) n = 3 , l = 0
it is 3s orbital . so, number of electrons in 3s orbital = 2