When an atom gains an electron, it undergoes a process called electron attachment or electron capture. During this process, an electron is added to the atom, typically occupying an empty orbital in one of the outer electron shells.
The energy change associated with the addition of an electron to an atom can vary depending on the specific atom and its electronic configuration. However, in general, an atom tends to release energy (become more stable) when it gains an electron. This release of energy occurs due to two main factors:
Electrostatic forces: When an electron is added to an atom, it is attracted to the positively charged nucleus due to the electrostatic force of attraction between opposite charges. This attraction releases energy, as the electron moves closer to the nucleus, lowering its potential energy.
Electron configuration and stability: The electronic structure of an atom is governed by specific energy levels or electron shells. These shells have different capacities for electron occupancy, and each shell is associated with a specific energy. The outermost shell, known as the valence shell, is particularly important in determining an atom's reactivity and stability.
When an atom gains an electron, it typically fills an empty orbital in its valence shell, resulting in a more stable electron configuration. This stability is achieved by achieving a full valence shell or by completing a partially filled shell. A full or complete electron shell configuration is energetically favorable and more stable, leading to a lower overall energy for the atom.
In summary, when an atom gains an electron, the release of energy occurs due to the attractive forces between the negatively charged electron and the positively charged nucleus, as well as the attainment of a more stable electron configuration. This energy release contributes to the overall stability of the atom.