Atomic StructureMedium
Question
Which of the following is correct set of 4 quantum number of $19\ ^{\text{th}\text{~}}$ electron in Chromium (Atomic number $= 24$ ) in accordance with Aufbau principle?
Options
A.$n = 3,\mathcal{l} = 2,\text{ }m = + 2,\text{ }s = + \frac{1}{2}$
B.$n = 3,\mathcal{l} = 2,\text{ }m = - 2,\text{ }s = + \frac{1}{2}$
C.$n = 4,\mathcal{l} = 1,m = 0,s = + \frac{1}{2}$
D.$n = 4,\mathcal{l} = 0,\text{ }m = 0,\text{ }s = + \frac{1}{2}$
Solution
Sol. [Key Concept: Cr is $\lbrack Ar\rbrack 4s^{1}3d^{5}$; the 19th electron enters $4s$, so $n = 4,\ \mathcal{l =}0,\ m = 0,\ s = + 1/2$.]
$$\ {Cr\ }_{1}{\text{ }s}^{2}2{\text{ }s}^{2}2p^{6}3{\text{ }s}^{2}3p^{6}4{\text{ }s}^{1}3{\text{ }d}^{5} $$$\Rightarrow \ 19^{\text{th}\text{~}}e^{-}$belongs to 4s subshell
$n = 4;\mathcal{l} = 0;m = 0;m_{s} = + \frac{1}{2}$ or $- \frac{1}{2}$
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