Final answer:
Ionization energy is the amount of energy needed to remove an electron from an atom in the gas phase, resulting in the formation of a positively charged ion. The first ionization energy refers to the removal of the most loosely bound electron, and higher ionization energies correspond to the removal of additional electrons.
Step-by-step explanation:
Ionization energy (IE) refers to the amount of energy required to remove an electron from an atom in the gas phase. An atom must absorb this energy to overcome the electrostatic forces holding the electron within the atom. This process generates a cation with a positive charge as follows: A(g) → A+ (g) + e−, emphasized by the equation ΔH = IE.
The first ionization energy (IE1) is specifically the energy required to remove the most loosely bound electron from a neutral atom to form a +1 charged ion. Elements with higher IE1 values are less likely to form cations because they hold onto their electrons more tightly, rendering the electron removal process more energy-intensive.
Subsequent ionization energies, such as the second ionization energy (IE2), refer to the energy required to remove additional electrons, producing ions with higher positive charges, like X2+. Each successive ionization energy is higher than the previous one, indicating an increased difficulty in removing more electrons from an ion.