Which element has the highest first ionization energy?

• A. F
• B. Ne
• C. Li
• D. He

Answer: (D)

Verified step by step guidance

1. Understand that the first ionization energy is the energy required to remove one mole of electrons from one mole of gaseous atoms to form cations.
2. Recall the general periodic trend: ionization energy increases across a period from left to right due to increasing nuclear charge and decreases down a group due to increasing atomic radius and electron shielding.
3. Compare the given elements: Li (Group 1, Period 2), F (Group 17, Period 2), Ne (Group 18, Period 2), and He (Group 18, Period 1).
4. Recognize that helium (He) is in the top right corner of the periodic table (Period 1, Group 18), which means it has a very small atomic radius and a high effective nuclear charge, leading to a very high first ionization energy.
5. Conclude that among the options, helium (He) has the highest first ionization energy because it holds its electrons most tightly due to its small size and strong nuclear attraction.