Question

indicate whether the following follow the aufbau principle
1 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s²
2 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰
3 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 5d¹⁰
4 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴
a. yes
b. no

Explanation:

Step1: Recall Aufbau Principle

Electrons fill lower - energy orbitals before higher - energy ones. The order of filling is $1s<2s<2p<3s<3p<4s<3d<4p<5s<4d<5p<6s<4f<5d<6p\cdots$.

Step2: Analyze 1st electron configuration

In $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}$, electrons should fill $4s$ before $3d$. So this does not follow Aufbau Principle.

Step3: Analyze 2nd electron configuration

For $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}$, it follows the correct order of orbital - filling according to Aufbau Principle.

Step4: Analyze 3rd electron configuration

In $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{2}4d^{10}5p^{6}6s^{2}5d^{10}$, it follows the correct order of orbital - filling as per Aufbau Principle.

Step5: Analyze 4th electron configuration

In $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{2}4d^{10}5p^{6}6s^{2}4f^{14}$, it follows the correct order of orbital - filling as per Aufbau Principle.

Answer:

1. B. no
2. A. yes
3. A. yes
4. A. yes