Question

Why 3p orbital filled before 4s orbital?

Answer 1

Explanation:

According to the aufbau principal the 4S orbital is lower in energy than the 3D orbital hence, it is filled first .

Answer 2

Answer:

First of all, it follows the Aufbau’s principle properly & as both 4s and 3d orbitals have (n+l) values saying electron will get at first into 3d than 4s but reverse case is happening. So, considering other factors are -

The reasons for higher energy orbitals are:  

1. Proximity from nucleus
2. Unstability of orbitals

For 3d orbital,

→ Its away from nucleus (as, l=2 i.e., d-orbital) which will result in lower forces of attraction towards nucleus.  

→ As, its farther from nucleus that’s why, its having higher energy and is unstable.

For 4s orbital,

→ Its nearer to nucleus (as, l=0 i.e., s orbital) which will result in higher forces of attraction towards nucleus.

→ As, its nearer from nucleus that’s why, its having lower energy and is stable.

Hence, 4s is more stable and less energetic than 3d.

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Explanation: