Question

What are the values of the quantum numbers of ${19}^{th}$ electron of scandium (Z = 21)?

• A. n = 4; l = 0; m = 0; $m_s$ = +1/2
• B. n = 4; l = 1; m = 0; $m_s$ = +1/2
• C. n = 4; l = 2; m = 1; $m_s$ = +1/2
• D. n = 4; l = 3; m = 2; $m_s$ = +1/2

Answer 1

The correct option is A n = 4; l = 0; m = 0; $m_s$ = +1/2

The electronic configuration of scandium (Z = 21) is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{1}4s^2$.
The ${19}^{th}$ electron of scandium enters 4s orbital. Hence, $n=4$.
For an electron in s orbital $l=0;m=0$.
Hence, the values of the quantum numbers of ${19}^{th}$ electron of scandium are $n=4;l=0;m=0;m_s=+1/2$.