Step 1: Identify all available subshells within the n=4$n=4$ energy shell
For principal quantum level n=4$n=4$, the allowed values of azimuthal quantum numbers (l$l$) are:
- 4s$4\text{s}$ (l=0$l=0$) arrow 1 orbital arrow 2 electrons capacity$\rightarrow 1 \text{ orbital} \rightarrow 2 \text{ electrons capacity}$
- 4p$4\text{p}$ (l=1$l=1$) arrow 3 orbitals arrow 6 electrons capacity$\rightarrow 3 \text{ orbitals} \rightarrow 6 \text{ electrons capacity}$
- 4d$4\text{d}$ (l=2$l=2$) arrow 5 orbitals arrow 10 electrons capacity$\rightarrow 5 \text{ orbitals} \rightarrow 10 \text{ electrons capacity}$
- 4f$4\text{f}$ (l=3$l=3$) arrow 7 orbitals arrow 14 electrons capacity$\rightarrow 7 \text{ orbitals} \rightarrow 14 \text{ electrons capacity}$
Step 2: Filter capacity using spin values
Every single spatial orbital holds exactly 2 electrons maximum; one with spin s=+(1)/(2)$s=+\frac{1}{2}$ and one with spin s=-(1)/(2)$s=-\frac{1}{2}$.
Total number of orbitals across n=4$n=4$ is:
1 + 3 + 5 + 7 = 16 orbitals$$1 + 3 + 5 + 7 = 16\text{ orbitals}$$
Thus, the total count of electrons featuring spin value s=+(1)/(2)$s=+\frac{1}{2}$ across these completely filled configurations is exactly 16$16$.
Pattern Recognition
Total orbitals in shell n$n$ is n²$n^2$. Since each orbital contributes exactly 1 electron with s=+(1)/(2)$s=+\frac{1}{2}$, capacity is simply n² = 4² = 16$n^2 = 4^2 = 16$.
Chapter Mix
Class 11 Chemistry: Structure of Atom