Question

Use Lewis structures to show how the following reaction involves the transfer of a Lewis base from one Lewis acid to another. Identify the Lewis acid and Lewis base. $$ \mathrm{CO}_{3}^{2-}+\mathrm{SO}_{2} \longrightarrow \mathrm{CO}_{2}+\mathrm{SO}_{3}^{2-} $$

Short answer

The Lewis base is \(\mathrm{CO}_{3}^{2-}\), which donates an electron pair to the Lewis acid \(\mathrm{SO}_{2}\), creating \(\mathrm{CO}_{2}\) and converting the Lewis acid into the product \(\mathrm{SO}_{3}^{2-}\).

Step-by-step solution

Understand Lewis Acids and Bases

Lewis acids are electron pair acceptors, while Lewis bases are electron pair donors. In this reaction, identify which reactant is donating an electron pair (Lewis base) and which one is accepting an electron pair (Lewis acid).

Draw the Lewis Structures

Draw the Lewis structures for each compound. The carbonate ion \(\mathrm{CO}_{3}^{2-}\) has a central carbon atom with double bonds to one oxygen and single bonds to two other oxygens, each with a negative charge. Sulfur dioxide \(\mathrm{SO}_{2}\) has a sulfur atom double bonded to each oxygen and a lone pair of electrons on sulfur.

Identify the Transfer of Lewis Base

The Lewis base in this reaction is the carbonate ion since it is donating an electron pair. The sulfur in \(\mathrm{SO}_{2}\) accepts the electron pair, making \(\mathrm{SO}_{2}\) the Lewis acid.

Show the Reaction Mechanism

The carbonate ion \(\mathrm{CO}_{3}^{2-}\) donates a pair of electrons to one of the oxygen atoms in \(\mathrm{SO}_{2}\), which leads to a rearrangement of bonds. The carbonate ion loses an oxygen, becoming \(\mathrm{CO}_{2}\), and the \(\mathrm{SO}_{2}\) gains an oxygen to become \(\mathrm{SO}_{3}^{2-}\).

Identify the Lewis Acid and Base in the Products

After the reaction, the sulfur in \(\mathrm{SO}_{3}^{2-}\) originally functioned as a Lewis acid and has completed its octet by accepting the oxygen from carbonate. The carbonate ion, after losing the oxygen, is now a molecule of carbon dioxide. The transfer of the Lewis base (oxygen ion) from carbonate to sulfur dioxide has turned the Lewis acid sulfur dioxide into the Lewis acid sulfate \(\mathrm{SO}_{3}^{2-}\).

Key concepts

Lewis Acids and Bases

Understanding Lewis acids and bases is central to grasping many chemical reactions. A Lewis acid is a substance that can accept an electron pair, whereas a Lewis base is capable of donating an electron pair. This definition extends the concept of acidity and basicity beyond protons to include any electron pair interactions.

When identifying Lewis acids and bases in a reaction, it's helpful to look for an element in a compound that has a vacant orbital or is electron-deficient – these tend to be good Lewis acids. On the flip side, species with lone pairs of electrons or negative charges, which can be used to form new bonds, typically act as Lewis bases. By recognizing these traits, students can accurately point out the roles of different reactants in a reaction. As part of improving the understanding of this concept, let's look at a real-world example:

In car engines, where nitrogen oxides are formed, these compounds act as Lewis acids, and they can be neutralized by Lewis bases in catalytic converters. Exploring such practical applications helps in appreciating the importance of this concept and deepening comprehension.

Electron Pair Transfer

The concept of electron pair transfer is at the heart of many chemical reactions and is essential in the formation of new compounds. During this type of transfer, a Lewis base donates a pair of electrons to a Lewis acid, resulting in a coordinate covalent bond. The ability of compounds to serve as donor or acceptor is a critical aspect of understanding how molecules interact and react with one another.

An excellent way to conceptualize electron pair transfer is by visualizing the movement of 'electron clouds' from one species to another during the course of a chemical reaction. For instance, in the reaction between ammonia (NH₃) and boron trifluoride (BF₃), the nitrogen atom in ammonia donates its lone pair to boron, which doesn't have a complete octet, thus creating a new bond. It's this electron-rich to electron-poor relationship that drives the fascinating chemistry of molecular interaction.

Chemical Reaction Mechanism

A chemical reaction mechanism is the step-by-step sequence of elementary reactions by which overall chemical change occurs. It plays a vital role in understanding how products are formed from reactants, acting almost like a 'playbook' showcasing the movements of electrons, rearrangement of bonds, and transformation of molecules.

To elucidate the importance of chemical reaction mechanisms, let's use the synthesis of water from hydrogen and oxygen as an example. To teach this effectively, it’s not enough to simply state that hydrogen and oxygen react to form water; students need to comprehend that oxygen molecules split into individual atoms, which then rapidly react with hydrogen molecules to produce water. Thus, illustrating mechanisms gives insights not just into 'what' happens but into 'how' and 'why' things happen on a molecular level. This deep dive into the intricacies of chemical reactions not only enhances student understanding but also stimulates their fascination with the marvellous complexity of chemistry.