What is defined as the energy needed to remove an electron from an atom?

Ionization energy is defined as the energy required to remove an electron from an atom in its gaseous state. This process involves overcoming the attractive force between the negatively charged electron and the positively charged nucleus. The higher the ionization energy, the more energy is needed to detach the electron, indicating that the electron is held more tightly by the nucleus.

Ionization energy is a critical concept in understanding chemical reactivity and the formation of ions. Atoms with low ionization energy are more likely to lose electrons and form positive ions, whereas those with high ionization energy tend to hold onto their electrons more tightly.

The other options refer to different energy concepts. Bonding energy is related to the energy required to break or form bonds between atoms within a molecule. Binding energy generally refers to the energy required to separate particles that are bound together, such as nucleons within an atomic nucleus. Kinetic energy is the energy of motion and is not specifically related to electronic processes within atoms. Thus, the term that directly describes the energy needed to remove an electron from an atom is ionization energy.