Question

Use Lewis structures to diagram the reaction $$ \mathrm{CO}_{2}+\mathrm{O}^{2-} \longrightarrow \mathrm{CO}_{3}^{2-} $$ Identify the Lewis acid and Lewis base in the reaction.

Short answer

CO2 is the Lewis acid and O2- is the Lewis base in the reaction forming a CO3^2- ion.

Step-by-step solution

Draw the Lewis structure of CO2

First, determine the total number of valence electrons. Carbon has 4 and each oxygen has 6, for a total of 16 valence electrons. Arrange the atoms with carbon in the middle and create double bonds between carbon and the two oxygen atoms to satisfy the octet rule for all atoms involved.

Draw the Lewis structure of O2-

Oxygen has 6 valence electrons naturally, and as it carries a 2- charge, it has 2 extra electrons, totaling 8. Distribute these electrons to provide an octet around the oxygen atom and indicate the 2- charge by placing brackets around the structure with the charge outside.

Show electrons transferring or sharing to form CO3^2-

Allow one of the double-bonded oxygen atoms in CO2 to share a pair of its electrons with the O2- ion, creating a single bond and consequently forming the CO3^2- ion. In the end, the carbonate ion will have one carbon in the center, double-bonded to one oxygen and single-bonded to two additional oxygens, each holding a negative charge.

Identify Lewis acid and base

In this reaction, CO2 is the Lewis acid as it accepts a pair of electrons from O2- ion. The O2- ion is the Lewis base as it donates a pair of electrons to form a bond with the carbon atom in CO2.

Key concepts

Lewis Acid and Base

Understanding Lewis acids and bases is essential for grasping many reactions in chemistry, including the formation of the carbonate ion. A Lewis acid is defined as an electron-pair acceptor, while a Lewis base is an electron-pair donor. This concept goes beyond the classic definition of acids and bases in terms of protons.

In the reaction \[\begin{equation}\mathrm{CO}_{2}+\mathrm{O}^{2-} \longrightarrow \mathrm{CO}_{3}^{2-}\end{equation}\]the carbon dioxide (\[\begin{equation}\mathrm{CO}_{2}\end{equation}\]) molecule acts as a Lewis acid because it accepts a pair of electrons from the oxide ion (\[\begin{equation}\mathrm{O}^{2-}\end{equation}\]), which is the Lewis base. This is a crucial concept because identifying the movement of electron pairs can help predict the course of a chemical reaction and the structure of the resulting compounds.

Valence Electrons

The outermost electrons of an atom are known as valence electrons. They play a key role in chemical bonding and reactions because they can be lost, gained, or shared to form chemical bonds. The number of valence electrons helps determine an element's chemical properties and its ability to bond with other elements.

In the case of the carbon dioxide and carbonate ion reaction, the carbon atom has 4 valence electrons, while each oxygen atom has 6. By following the octet rule, which states that atoms tend to bond in such a way that each atom has eight electrons in its valence shell, we can predict how these atoms will combine. When drawing Lewis structures, it's important to count valence electrons accurately and distribute them to achieve stable electron configurations for the resulting molecule or ion.

Carbonate Ion

The carbonate ion (CO₃^2-) is a fundamental polyatomic ion, which is a charged species composed of more than one atom. It consists of one carbon atom surrounded by three oxygen atoms in a trigonal planar arrangement. Two of the oxygen atoms are single-bonded to carbon, each carrying a negative charge, while the third is double-bonded to carbon, completing its octet without a formal charge.

Understanding the Lewis structure of the carbonate ion helps us visualize not only its electron distribution but also the resonance structures it can form. The negative charges on the carbonate ion are delocalized, meaning that the actual structure is a hybrid of multiple possible arrangements of the double bond. This is an important concept in chemistry because it impacts the carbonate ion's reactivity and interaction with other substances, such as the formation of salts with metal ions.