Question

Which of the following explains the sequence of filling the electrons in different shells?

• A. Aufbau principle
• B. Octet rule
• C. Hund?s rule
• D. All of these

Answer 1

Answer: (A)

Aufbau principle

Answer 2

According to Aufbau principle, the subshell with minimum energy is filled up first and when this obtains maximum quota of electrons, then the next subshell of higher energy starts filling. So subshell with lowest $(n +l)$ value is filled first. Sequence comes out to be $: 1 s,\, 2 s,\, 2 p,\, 3 s,\, 3 p,\, 4 s,\, 3 d,\, 4 p,\, 5 s,\, 4 d,\, 5 p,\, 6 s,\, 4 f$ etc.