A Level Chemistry OCR Practice Exam

Which statement best describes first ionization energy?

1. The energy to remove two electrons from an atom

2. The energy required to remove one electron from each ion in one mole of gaseous ions

3. The total energy required to ionize all electrons in an atom

4. The energy released when an electron is added to an atom

The correct answer is: The energy required to remove one electron from each ion in one mole of gaseous ions

First ionization energy is defined as the energy required to remove the outermost electron from a neutral atom in its gaseous state to form a positively charged ion. This process occurs for one mole of atoms, meaning that the energy measured corresponds to the removal of a single electron per atom rather than multiple electrons or the complete ionization of the atom. The choice emphasizing the energy needed to remove one electron from each ion in one mole of gaseous ions accurately captures this definition. Ionization energy is typically specified for a single electron being removed during a single ionization event, hence linking this concept specifically to first ionization energy. In contrast, some of the other options incorrectly describe the ionization process. For example, the statement regarding removing two electrons misconstrues the definition, as first ionization energy only pertains to the removal of one electron. The option discussing total energy for all electrons also misrepresents the concept, as it refers to successive ionization energies rather than specifically the first ionization energy. Lastly, the statement regarding energy release upon adding an electron relates to electron affinity, which is a different process altogether and does not apply to ionization energies.