Answer
See the explanation
Work Step by Step
The first ionization energy refers to the energy required to remove one electron from an atom in its gaseous state. It is influenced by factors such as the atomic radius, effective nuclear charge, and electron configuration.
In the case of As (arsenic), its electron configuration is [Ar] 3d¹⁰ 4s² 4p³. Arsenic has five valence electrons in its outermost shell (4s² 4p³). These valence electrons experience a relatively weak effective nuclear charge due to shielding by the inner electrons. As a result, it is easier to remove one of these valence electrons, leading to a lower first ionization energy.
On the other hand, Se (selenium) has an electron configuration of [Ar] 3d¹⁰ 4s² 4p⁴. Selenium also has five valence electrons in its outermost shell (4s² 4p⁴). However, compared to arsenic, selenium has a slightly smaller atomic radius and a higher effective nuclear charge. The increased attraction between the nucleus and the valence electrons makes it more difficult to remove one of these electrons, resulting in a slightly higher first ionization energy compared to arsenic.
Therefore, the rationalization of the given values is that arsenic (As) has a lower first ionization energy (0.947 MJ/mol) compared to selenium (Se) (0.941 MJ/mol) due to the differences in their electron configurations and the resulting atomic properties.
