Chapter 3: Problem 24

Why does an electron occupy the 4s orbital before the 3\(d\) orbital?

Short Answer

Expert verified

An electron occupies the 4s orbital before the 3d orbital because it is of lower energy due to its efficient penetration into the lower electron shell. This efficient penetration results in a larger nuclear charge and hence lower energy.

Step by step solution

Understanding Electron Configurations

Electrons in an atom are arranged in shells and sub-shells. The energy levels, shells, are labeled as n=1, 2, 3, etc., while sub-shells, also called orbitals, are labelled as s, p, d, f etc. The 3d and 4s are types of orbitals.

Introduction to the Aufbau Principle

The Aufbau Principle states that electrons fill lower energy levels, or orbitals, before moving to higher ones. This is a general rule for electron configurations.

Difference between 3d and 4s Energy Levels

The 3d orbital is in the third energy level, and the 4s orbital is in the fourth. However, the relative energies of these orbitals aren't exactly what you might assume based on their order in the periodic table. Each 4s orbital's energy is slightly lower than the energy of the 3d orbitals; that's why electrons gravitate towards 4s before filling the 3d orbitals.

Reason behind Filling Order of Orbits

The reason that the 4s orbital gets filled before the 3d is due to the shape and shielding. The 4s electrons penetrate more efficiently into the lower electron shell than 3d electrons. Therefore, they experience a larger nuclear charge and correspondingly lower energy.

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Why does an electron occupy the 4s orbital before the 3\(d\) orbital?

Short Answer

Step by step solution

Understanding Electron Configurations

Introduction to the Aufbau Principle

Difference between 3d and 4s Energy Levels

Reason behind Filling Order of Orbits

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