Quantum Mechanics and Electron Configurations - SS2 Physics Lesson Note

Quantum mechanics is a fundamental theory in physics that describes the behaviour of particles at the atomic and subatomic levels. It provides a mathematical framework to understand the properties and interactions of particles, including electrons in atoms.

Wave-Particle Duality:

Quantum mechanics introduces the concept of wave-particle duality, which suggests that particles, including electrons, can exhibit both wave-like and particle-like behaviours. Electrons are described by wavefunctions, which are mathematical functions that represent the probability distribution of finding an electron in a particular state.

Energy Levels and Quantization:

According to quantum mechanics, electrons in atoms can only occupy certain energy levels, which are quantized. These energy levels are often represented by principal quantum numbers (n) and are organised into different shells or orbitals. The energy of an electron increases with higher values of n.

Electron Configurations:

The arrangement of electrons in an atom is known as its electron configuration. It describes how electrons occupy the available energy levels and orbitals. The Pauli exclusion principle states that no two electrons in an atom can have the same set of quantum numbers, meaning that each electron must have a unique set of quantum numbers.

Aufbau Principle:

The Aufbau principle is a guideline for constructing electron configurations. It states that electrons fill the lowest energy levels first before moving to higher energy levels. Electrons follow the order of increasing energy, which is determined by the principal quantum number (n) and the effective nuclear charge experienced by the electron.

Hund's Rule:

Hund's rule states that when filling orbitals with multiple electrons of the same energy level, electrons will occupy separate orbitals with parallel spins before pairing up. This arrangement maximises the total spin and minimises electron-electron repulsion.

Notation of Electron Configurations:

Electron configurations are often represented using a notation that indicates the energy level and the number of electrons in each orbital. The notation follows the pattern of specifying the principal quantum number (n), the orbital letter (s, p, d, f), and the superscript indicating the number of electrons.

Exceptions and Transition Elements:

Some elements deviate from the expected electron configurations due to the stability of half-filled or completely filled subshells. Transition elements, for example, may have different electron configurations in their outermost energy levels, allowing for variations in their chemical properties.

Quantum mechanics revolutionised our understanding of electron behaviour and provided a comprehensive framework to describe electron configurations in atoms. It allows for precise calculations of atomic properties, spectral lines, chemical reactivity, and the electronic structure of molecules. The electron configuration of an atom provides valuable information about its chemical behaviour, bonding tendencies, and overall stability.