Advanced Placement (AP) Chemistry Practice Exam

What does ionization energy measure?

1. The energy needed to bond two atoms

2. The energy required to remove electrons from an atom

3. The energy released during electron capture

4. The energy change when forming ionic compounds

The correct answer is: The energy required to remove electrons from an atom

Ionization energy specifically refers to the energy required to remove an electron from an atom or ion in its gaseous state. This process involves overcoming the attractive force between the positively charged nucleus and the negatively charged electron. The greater the ionization energy, the more difficult it is to remove an electron, which indicates a stronger attachment of the electron to the nucleus. Option B accurately captures this definition, highlighting that ionization energy is fundamentally about the energy needed to detach an electron from an atom, making it a key concept in understanding atomic structure and reactivity. The other options relate to different chemical phenomena but do not define ionization energy. For instance, while bonding two atoms involves energy considerations, it is not the focus of ionization energy. Electron capture relates to a different process altogether, where an electron is added rather than removed, leading to various reactions and energy changes that do not describe ionization. Similarly, the energy changes associated with forming ionic compounds concern lattice energy and other interactions, which are separate from the concept of ionization energy.