aufbau principle

Question

According to the Aufbau principle, which orbital is filled before 4p?

RankGuru · Accepted Answer

The **Aufbau Principle** dictates that orbitals are filled in increasing order of energy, following the $(n+l)$ rule:
1. **3d**: $n=3, l=2 \implies n+l = 5$
2. **4p**: $n=4, l=1 \implies n+l = 5$
- When $(n+l)$ values are equal, the orbital with the **lower value of $n$** has lower energy and is filled first.
- Therefore, $3d$ ($n=3$) is filled before $4p$ ($n=4$).
Filling order: $\dots 4s 	o 3d 	o 4p \dots$

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aufbau principle

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