A Level Physics Practice Exam - 2026 Practice Test & Study Guide

An electron with no excess energy occupies the ground state of an atom. The ground state is defined as the lowest energy configuration of an electron in an atom, meaning it is at its most stable condition. In this state, electrons are not in any higher energy levels and cannot lose or gain energy in the form of photons or other interactions.

When an electron is in the ground state, it is filled in accordance with the principles of quantum mechanics, where it occupies the closest possible orbit around the nucleus. This state is essential for the stability of the atom and is the basis for understanding atomic structure and behavior.

In contrast, an excited state refers to an electron that has absorbed energy and moved to a higher energy level. An ionized state involves an electron being completely removed from the atom, leading to a charged ion, while a transient state describes a temporary condition that may occur during energy transitions but does not define a stable configuration for the electron in the absence of excess energy.