What is meant by ionization energy?

Ionization energy refers to the energy required to remove an electron from an isolated gaseous atom or ion. This process involves overcoming the electrostatic attraction between the positively charged nucleus and the negatively charged electron. As a concept, it is fundamental in understanding how atoms interact, as it reflects the tendency of an atom to hold onto its electrons.

The correct answer highlights that ionization energy specifically quantifies how much energy is needed to detach an electron, forming a cation in the process. This is significant because the ionization energy can vary depending on the type of atom and its electron configuration, often increasing across a period on the periodic table due to greater nuclear charge and decreasing down a group because of increased distance and shielding effect.

In contrast, other choices address different concepts: adding an electron involves electron affinity, while energy released during ion formation is related to exothermic processes. Lastly, breaking a bond in a molecule pertains to bond dissociation energy, not ionization energy. Understanding these distinctions is crucial in the study of atomic behavior and chemical reactivity.