The behavior of electrons in an atom is described by quantum mechanics, which introduces the concept of electron orbitals or electron probability distributions rather than classical orbits. According to quantum mechanics, electrons do not orbit the nucleus in a classical sense like planets orbiting the Sun. Instead, they occupy specific energy levels or orbitals around the nucleus.
Each electron orbital corresponds to a specific energy level and has a characteristic shape and size. These orbitals are often represented as three-dimensional regions where the electron is likely to be found. The shape of an orbital is determined by the quantum numbers associated with the electron, which specify its energy, angular momentum, and orientation.
Electrons occupy the lowest available energy levels or orbitals first, following a set of rules known as the Aufbau principle, Pauli exclusion principle, and Hund's rule. The Aufbau principle states that electrons fill orbitals in order of increasing energy. The Pauli exclusion principle states that no two electrons in an atom can have the same set of quantum numbers, which means each orbital can accommodate a maximum of two electrons with opposite spins. Hund's rule states that when multiple orbitals of the same energy level are available, electrons will first occupy these orbitals singly with parallel spins before pairing up.
As for the decay of electrons, stable electrons in their ground state (lowest energy level) do not spontaneously decay within an atom. However, under certain circumstances, such as the absorption or emission of photons or interactions with other particles, electrons can transition between energy levels. These transitions may involve the emission or absorption of electromagnetic radiation, resulting in the emission or absorption of photons.
It's important to note that quantum mechanics provides a probabilistic description of electron behavior, meaning that we can predict the likelihood of finding an electron in a particular region around the nucleus. However, we cannot precisely determine the exact path or trajectory of an electron at any given moment.