Question

What do each of the following sets of compounds/ions have in common with each other? a. ${\mathrm{SO}}_3,{\mathrm{NO}}_3^{-},{\mathrm{CO}}_3^{2-}$ b. ${\mathrm{O}}_3,{\mathrm{SO}}_2,{\mathrm{NO}}_2-$

Short answer

The compounds/ions in set a, ${\mathrm{SO}}_3,{\mathrm{NO}}_3^{-},{\mathrm{CO}}_3^{2-}$, have a common feature: all the central elements - sulfur, nitrogen, and carbon - are in their highest possible oxidation states (+6, +5, and +4, respectively). The compounds/ions in set b, ${\mathrm{O}}_3,{\mathrm{SO}}_2,{\mathrm{NO}}_2^{-}$, have a common feature: Due to the presence of double bonds or resonance, each of the compounds has a central element with an intermediate oxidation state (0 for oxygen in ${\mathrm{O}}_3$, +4 for sulfur in ${\mathrm{SO}}_2$, and +3 for nitrogen in ${\mathrm{NO}}_2^{-}$).

Step-by-step solution

Set a. ${\mathrm{SO}}_3,{\mathrm{NO}}_3^{-},{\mathrm{CO}}_3^{2-}$

First, let us identify the oxidation state of the central element in each compound/ion. We have sulfur in ${\mathrm{SO}}_3$, nitrogen in ${\mathrm{NO}}_3^{-}$, and carbon in ${\mathrm{CO}}_3^{2-}$. Since each of these compounds exhibits resonance, the average oxidation state of the central element can be found as follows: - In ${\mathrm{SO}}_3$: The oxidation state of oxygen is always -2. So, for a neutral compound, the oxidation state of the sulfur must be $+6$ in order for the overall compound to have a net charge of 0. - In ${\mathrm{NO}}_3^{-}$: The oxidation state of oxygen is -2 as well. Since the net charge of the ion is -1, the oxidation state of the nitrogen must be $+5$ to maintain the total charge. - In ${\mathrm{CO}}_3^{2-}$: Oxygen maintains an oxidation state of -2. To achieve a net charge of -2, the oxidation state of carbon must be $+4$.

Common feature of set a

The compounds/ions in set a, ${\mathrm{SO}}_3,{\mathrm{NO}}_3^{-},{\mathrm{CO}}_3^{2-}$, have a common feature: all the central elements - sulfur, nitrogen, and carbon - are in their highest possible oxidation states (+6, +5, and +4, respectively).

Set b. ${\mathrm{O}}_3,{\mathrm{SO}}_2,{\mathrm{NO}}_2^{-}$

Now, let's determine the oxidation states of the central elements in each compound/ion. In this set, we have ozone $({\mathrm{O}}_3)$, sulfur dioxide $({\mathrm{SO}}_2)$, and nitrite $({\mathrm{NO}}_2^{-})$. We will again focus on the average oxidation state of the central element in each compound/ion: - In ${\mathrm{O}}_3$: Oxygen, being the only element, has an average oxidation state of 0. - In ${\mathrm{SO}}_2$: Oxygen keeps an oxidation state of -2. For the compound to be neutral, the oxidation state of sulfur must be $+4$. - In ${\mathrm{NO}}_2^{-}$: Oxygen still has an oxidation state of -2. Given the overall ion has a -1 charge, the oxidation state of nitrogen must be $+3$.

Common feature of set b

The compounds/ions in set b, ${\mathrm{O}}_3,{\mathrm{SO}}_2,{\mathrm{NO}}_2^{-}$, have a common feature: Due to the presence of double bonds or resonance, each of the compounds has a central element with an intermediate oxidation state (0 for oxygen in ${\mathrm{O}}_3$, +4 for sulfur in ${\mathrm{SO}}_2$, and +3 for nitrogen in ${\mathrm{NO}}_2^{-}$).

Key concepts

Resonance

Resonance is a fascinating phenomenon in chemistry that provides insight into the stability and behavior of molecules. It occurs when a molecule can be represented by two or more valid Lewis structures, known as resonance structures. These structures differ only in the placement of electrons, not the arrangement of atoms.
For example, in nitrate (${\text{NO}}_3^{-}$), each oxygen atom shares a double bond with nitrogen at different positions in its resonance forms. This doesn't mean the molecule is switching between these forms; instead, the actual structure is a blend, called a resonance hybrid. This hybrid gives a more accurate representation of the molecule's electron distribution.

• This delocalization of electrons contributes to the stability of ions and molecules.
• Resonance is not indicated by movement but by superimposition of resonance forms.
• It minimizes the energy of the actual structure.

Understanding resonance helps in predicting how molecules react and how they interact with others.

Central Elements

The central element in a compound plays a crucial role in determining its chemical behavior and properties. It is typically the atom that is bonded to the largest number of other atoms in the structure.
In the compounds mentioned in the exercise, sulfur, nitrogen, and carbon often act as central elements because they can form multiple bonds to satisfy electron deficiency.
The oxidation state of a central element provides key insights into its chemical nature:

• It indicates how electrons are distributed among bonded atoms.
• Helps predict and explain the reactivity and potential compounds formed.
• In certain sets of compounds, like those in set a of the exercise (${\text{SO}}_3$, ${\text{NO}}_3^{-}$, and ${\text{CO}}_3^{2-}$), the central elements are at their highest possible oxidation states.

This means they're in a state where they've lost the maximum number of electrons achievable by that element during chemical bonding, making them powerful oxidizing agents.

Compound/Ion Structures

The structure of a compound or ion directly impacts its chemical properties, behavior, and stability. Understanding the shapes and arrangements of compounds/ions can reveal a lot about their potential reactions and interactions.
In the case of set a (${\text{SO}}_3$, ${\text{NO}}_3^{-}$, ${\text{CO}}_3^{2-}$), these compounds share a trigonal planar geometry around their central elements. This specific arrangement minimizes electron repulsion, leading to stable configurations.

• In a trigonal planar structure, atom groups are evenly distributed around the central atom.
• This arrangement allows for strong bonds due to favorable orbital overlap.
• The symmetry in the structure contributes to the compound's stability and reactivity.

Meanwhile, the second set of compounds (${\text{O}}_3$, ${\text{SO}}_2$, ${\text{NO}}_2^{-}$) often shows a bent shape due to the presence of lone pairs or resonance. Understanding these structures and their impacts on chemical behavior can aid in predicting how these compounds will engage in chemical reactions.