Kaplan Nursing Entrance Practice Exam

What does ionization energy refer to?

1. Energy required to remove the outermost electron from an atom

2. Energy required to form a covalent bond

3. Energy released during electron gain

4. Energy needed for phase changes

The correct answer is: Energy required to remove the outermost electron from an atom

Ionization energy specifically pertains to the amount of energy that is necessary to remove the outermost electron from a neutral atom in its gaseous state. This process plays a significant role in determining the reactivity of elements, especially in the context of how readily an atom can form positive ions. The higher the ionization energy, the more energy is required to detach that electron, which typically indicates that the atom is less likely to lose an electron and become a cation. Factors affecting ionization energy include the nuclear charge, the distance of the outermost electron from the nucleus, and electron shielding or screening effects. As you move across a period in the periodic table, ionization energy tends to increase due to the increasing nuclear charge, while it generally decreases down a group because of increased distance and shielding from inner electrons. In contrast, forming a covalent bond involves different energy considerations and pertains to the attraction between atoms sharing electrons. The energy released during electron gain refers to electron affinity, not ionization. Lastly, energy needed for phase changes relates to the changes of state of matter, which is outside of the considerations for ionization energy. Hence, the correct understanding of ionization energy is centered around the energy needed to remove an electron from an atom.