Which of the following elements is predicted to have the greatest (most endothermic) first ionization energy?

• A. Na (sodium)
• B. Li (lithium)
• C. K (potassium)
• D. Ne (neon)

Answer: (D)

Verified step by step guidance

1. Understand that the first ionization energy is the energy required to remove one electron from a neutral atom in the gas phase.
2. Recall the general trend in the periodic table: ionization energy increases across a period (left to right) and decreases down a group (top to bottom).
3. Identify the positions of the given elements: Na, Li, and K are all alkali metals in Group 1, with Li at the top, Na below it, and K further down the group.
4. Recognize that Neon (Ne) is a noble gas located at the end of the second period, which means it has a full valence shell and a very stable electron configuration.
5. Conclude that because Ne has a full octet and is at the right end of the period, it will have a much higher (more endothermic) first ionization energy compared to the alkali metals, which have only one valence electron and are more willing to lose it.