Question

Select which of the following ions has the Lewis structure: $$ [: \ddot{\mathrm{X}}-\ddot{\mathrm{X}}:\rfloor^{2-} $$ a. \(\mathrm{B}_{2}^{2-}\) b. \(\mathrm{C}_{2}^{2-}\) c. \(\mathrm{N}_{2}^{2-}\) d. \(\mathrm{O}_{2}^{2-}\) e. \(\mathrm{F}_{2}^{2-}\)

Short answer

The correct diatomic ion corresponding to the given Lewis structure is c. N₂²⁻ due to its total valence electron count (12 electrons) which matches the total required by the Lewis structure.

Step-by-step solution

Understand the given Lewis structure

The given Lewis structure represents a diatomic ion with two single bonds and two lone pairs on each atom. We also know that the ion has a charge of 2-, meaning two extra electrons. Our task is to find which diatomic ion is represented by this Lewis structure.

Count valence electrons for each ion

We begin by identifying the valence electrons for each of the candidate ions. a. B₂ has 3 valence electrons per atom. B2²⁻ ion has a total of 8 valence electrons. b. C₂ has 4 valence electrons per atom. C2²⁻ ion has a total of 10 valence electrons. c. N₂ has 5 valence electrons per atom. N2²⁻ ion has a total of 12 valence electrons. d. O₂ has 6 valence electrons per atom. O2²⁻ ion has a total of 14 valence electrons. e. F₂ has 7 valence electrons per atom. F2²⁻ ion has a total of 16 valence electrons.

Compare candidate ions' valence electrons with the given Lewis structure

To find the correct ion, we need to find the ion with a total valence electron count that matches the total count from our given Lewis structure. According to the given Lewis structure, we have: - 2 single bonds: Each single bond has 2 electrons, so 2 single bonds contribute 4 electrons. - 2 lone pairs per atom: Each lone pair has 2 electrons, so 4 lone pairs (2 on each atom) contribute 8 electrons. - Total of 12 electrons in the structure. Now, comparing our candidates to the given Lewis structure, we find that N₂²⁻ (option c.) has 12 valence electrons, which matches the requirement. So, the correct answer is: c. N₂²⁻

Key concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom. They are primarily involved in chemical bonding. The number of valence electrons in an atom determines its ability to interact with other atoms.
For example, an oxygen atom has 6 valence electrons, which influences how it forms bonds and interacts with other elements. Understanding the valence electrons of each atom helps predict how atoms bond to form molecules or ions.
This is a crucial step in building Lewis structures. By counting the valence electrons, students can ensure that all atoms fulfill the octet rule, a guideline that suggests atoms tend to bond in such a way that they have eight electrons in their outer shell.

Diatomic Ion

A diatomic ion is a molecule composed of two atoms that carries an overall electrical charge. These ions result from the combination of two identical or different atoms.
In the context of our exercise, each option represents a diatomic ion with a charge of 2-. For example, \(N_2^{2-}\)is a diatomic ion formed by two nitrogen atoms sharing electrons and possessing extra electrons to reach a 2- charge. These ions demonstrate how atoms with similar electronegativities can also gain or lose electrons, resulting in stable charged species.

Ionic Charge

The ionic charge is the electrical charge an ion possesses due to the gain or loss of electrons. When an atom gains electrons, it becomes negatively charged, whereas losing electrons results in a positive charge.
An ion such as \(N_2^{2-}\)has gained two additional electrons in total, giving it the negative charge indicated in its formula. Knowledge of ionic charge is crucial in determining the ionic formula and the correct Lewis structure. The process involves adjusting the number of electrons in the outer shell to achieve notable electron configurations, often adhering to the octet rule for greater stability.

Chemical Bonding

Chemical bonding describes the force holding atoms together in molecules and compounds. There are several types of bonds, but covalent bonds, where electrons are shared between atoms, and ionic bonds, where electrons are transferred, are most common.
For diatomic ions in this case, the shared electrons form covalent bonds. Each nitrogen atom shares a lone pair of electrons with the other, forming a stable ion with a 2- charge, as depicted in the Lewis structure. Chemical bonding is foundational to understanding molecular behavior, shapes, and reactivity in chemistry.