Problem 24 Why does an electron occupy the ... [FREE SOLUTION]

Chapter 3: Problem 24

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

Short Answer

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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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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Aufbau Principle

The Aufbau Principle is a fundamental guideline used when determining the electron configuration of an atom. In simple terms, it suggests that electrons fill atomic orbitals in a way that minimizes the energy of the atom. This means that electrons will occupy the lowest energy orbitals available before moving to higher energy levels.

Lowest Energy First: Electrons begin to fill from the lowest energy orbital, working their way up.
Foundation for Electron Configuration: The principle serves as the foundation for understanding how the electrons are arranged in orbitals around the nucleus of an atom.
Consistent Filling Order: This concept helps predict the order of orbital filling in atoms, further facilitating comprehension of atomic structure and chemical bonding.

By following the Aufbau Principle, we can achieve a stable and balanced electron configuration, which reflects the natural tendency of atoms to seek their lowest energy state.

Energy Levels

Energy levels, often visualized as electron shells, are the distances at which electrons orbit the nucleus of an atom. These shells can be thought of as layers where each can hold a specific number of electrons. The concept of energy levels is crucial when discussing electron configuration because it dictates how electrons are distributed around an atom's nucleus.

Notation: Energy levels are denoted by the principal quantum number, \( n \), where \( n = 1 \) is the closest to the nucleus.
Increasing Energy: As \( n \) increases, so does the potential energy of the electrons. Higher energy levels correspond to orbitals further from the nucleus.
Filling Order: Electrons fill lower energy levels first, following a specific sequence known as the orbital filling order.

Understanding energy levels helps explain why electrons might occupy, for instance, the 4s orbital before the 3d, despite the 3d being labeled with a lower principal quantum number.

Orbital Filling Order

The orbital filling order is the sequence in which orbitals are populated when arranging electrons during the formation of atoms. It is influenced by the shapes and relative energies of the orbitals, which dictate the specific order in which they are filled.

Order Variation: The order might not always follow a simple numeric sequence; some orbitals, like the 4s, fill before others, like the 3d.
Factors Influencing Order: The filling order is affected by electron penetration and shielding which alter the effective energy of orbitals.
Importance of Shape and Distance: The 4s orbital, for example, will fill before the 3d due to its slightly lower energy level.

This concept clarifies why electrons in atoms such as potassium (K) and calcium (Ca) first fill the 4s orbital rather than immediately occupying the 3d orbitals, due to factors like penetration and effective nuclear charge.

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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

Key Concepts

Aufbau Principle

Energy Levels

Orbital Filling Order

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