Which of the following best explains why it is easier to remove a 2p electron from an oxygen atom than from a nitrogen atom?

• A. Oxygen has a lower nuclear charge than nitrogen, so its electrons are less tightly held.
• B. Oxygen has a completely filled 2p subshell, making its electrons easier to remove.
• C. Nitrogen's 2p electrons are farther from the nucleus than those in oxygen, making them easier to remove.
• D. In oxygen, electron-electron repulsion in the paired 2p electrons makes it easier to remove one, whereas nitrogen has half-filled 2p orbitals with greater stability.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the electronic configurations of nitrogen and oxygen atoms, focusing on their 2p subshells. Nitrogen has the configuration 1s\^2 2s\^2 2p\^3, meaning its 2p orbitals are half-filled with one electron each, while oxygen has 1s\^2 2s\^2 2p\^4, with one of the 2p orbitals containing a pair of electrons.
2. Step 2: Recall that half-filled subshells (like nitrogen's 2p\^3) are particularly stable due to electron exchange energy and minimized electron-electron repulsion, which makes removing an electron from nitrogen more difficult.
3. Step 3: Recognize that in oxygen, the presence of paired electrons in one of the 2p orbitals increases electron-electron repulsion, which destabilizes that electron pair and makes it easier to remove one electron from oxygen compared to nitrogen.
4. Step 4: Note that nuclear charge actually increases from nitrogen to oxygen, so oxygen's electrons are generally held more tightly, but the increased repulsion in oxygen's paired 2p electrons overrides this effect when considering ionization energy.
5. Step 5: Conclude that the key reason it is easier to remove a 2p electron from oxygen than nitrogen is the increased electron-electron repulsion in oxygen's paired 2p electrons, which reduces the energy required to remove one electron.