Arrange the atoms N, F, and As in order of decreasing first-ionization energy.
A) N > As > F
B) As > N > F
C) F > N > As
D) As > F > N
The correct answer and explanation is :
The correct answer is C) F > N > As.
Explanation:
First-ionization energy refers to the amount of energy required to remove one mole of electrons from one mole of atoms in their gaseous state. This property varies across the periodic table, depending on several factors such as the atomic number, the distance of the electrons from the nucleus, and the effective nuclear charge experienced by the outermost electron.
To determine the order of decreasing first-ionization energies for nitrogen (N), fluorine (F), and arsenic (As), we need to consider their positions on the periodic table and their electronic structures:
- Fluorine (F):
- Fluorine is in Group 17 (the halogens), Period 2. It has the electronic configuration of (1s^2 2s^2 2p^5).
- Fluorine has a high effective nuclear charge due to its relatively small atomic size and high electronegativity. This means the outermost electron is tightly bound to the nucleus, requiring a higher amount of energy to remove it compared to other elements.
- Nitrogen (N):
- Nitrogen is in Group 15, Period 2, with the electronic configuration of (1s^2 2s^2 2p^3).
- Although nitrogen has a half-filled (2p)-subshell (which provides some stability), it still has a higher ionization energy than arsenic. The effective nuclear charge is relatively high for nitrogen due to its small atomic size and the same period as fluorine, but it is less than fluorine’s due to its lower electronegativity.
- Arsenic (As):
- Arsenic is in Group 15, Period 4, with the electronic configuration ( [Ar] 4s^2 3d^{10} 4p^3 ).
- Arsenic is much larger than both nitrogen and fluorine, and its outermost electrons are farther from the nucleus. Additionally, the shielding effect of the inner electron shells reduces the effective nuclear charge experienced by the outermost electron. As a result, the first-ionization energy of arsenic is significantly lower than both nitrogen and fluorine.
Thus, the order of first-ionization energies from highest to lowest is Fluorine > Nitrogen > Arsenic (C).