Question

which atom has the smallest first ionization energy? c be b o n

Explanation:

Ionization energy is the energy required to remove an electron from an atom. In a period (horizontal row in the periodic table), ionization energy generally increases from left to right. However, there are exceptions. Beryllium (Be) has an electron configuration of \(1s^{2}2s^{2}\), boron (B) has \(1s^{2}2s^{2}2p^{1}\). Removing an electron from B's \(2p\) orbital (which is higher in energy than the \(2s\) orbital) is easier than expected because the \(2p\) electron in B experiences less effective nuclear charge compared to the trend. Carbon (C: \(1s^{2}2s^{2}2p^{2}\)), nitrogen (N: \(1s^{2}2s^{2}2p^{3}\), half - filled \(2p\) stability), and oxygen (O: \(1s^{2}2s^{2}2p^{4}\), electron - electron repulsion in \(2p\) but still higher ionization energy than B due to overall increasing trend) have higher first ionization energies than B.

Answer:

B. B