Question

Write the resonance structures of \(\mathrm{CO}_{3}^{2-}\) and \(\mathrm{HCO}_{3}^{-}\).

Short answer

\(\mathrm{CO}_{3}^{2-}\) has 3 resonance structures; \(\mathrm{HCO}_{3}^{-}\) has 2 resonance structures.

Step-by-step solution

Understanding Resonance Structures

Resonance structures are different ways to draw a molecule by distributing electrons differently across the same arrangement of atoms. Though the actual molecule is a blend of these structures, resonance structures highlight possible, not real, electron distributions.

Identify the Molecular Structure of (\mathrm{CO}_{3}^{2-})

The carbonate ion, \((\mathrm{CO}_{3}^{2-})\), consists of one carbon atom centrally connected to three oxygen atoms arranged in a trigonal planar shape. Each oxygen is either doubly or singly bonded, while maintaining the total 2- charge.

Draw the Resonance Structures of (\mathrm{CO}_{3}^{2-})

There are 3 resonance structures for \((\mathrm{CO}_{3}^{2-})\):1. One double bond between carbon and one oxygen, with the other two oxygen atoms having single bonds.2. Shift the double bond to the next oxygen atom and redraw.3. Repeat for the remaining oxygen. All of these configurations balance the charge of \(2-\) across oxygens.

Identify the Molecular Structure of (\mathrm{HCO}_{3}^{-})

The bicarbonate ion, \((\mathrm{HCO}_{3}^{-})\), consists of one carbon centrally bonded to three oxygen atoms and one of these oxygen atoms bonded to a hydrogen atom.

Draw the Resonance Structures for (\mathrm{HCO}_{3}^{-})

There are 2 main resonance structures for \((\mathrm{HCO}_{3}^{-})\):1. One structure has a double bond between the carbon and one of the oxygens, with the hydrogen attached to one of the singly bonded oxygens.2. Shift the double bond to the next singly bonded oxygen to complete the resonance pattern. The position of the hydrogen remains fixed.

Key concepts

Carbonate Ion

The carbonate ion, represented as \(\mathrm{CO}_{3}^{2-}\), is an ion that features a central carbon atom surrounded by three oxygen atoms. It showcases a trigonal planar geometry, which essentially means that the oxygen atoms form an equilateral triangle around the carbon atom. Each of these oxygen atoms can potentially form a double bond with the carbon, resulting in multiple possible electron configurations.

• Each carbon-oxygen bond can be either a single or double bond.
• The overall charge of the carbonate ion is \(-2\).
• There are three possible resonance structures for \(\mathrm{CO}_{3}^{2-}\).

In these resonance structures, the position of the double bond rotates among the oxygen atoms, ensuring that the total number of electrons remains constant. The true structure of the carbonate ion is a hybrid, meaning it is a blend of all these resonance structures, providing it with stability. This hybrid represents an average where the electron density is evenly distributed across the oxygen atoms, thus each one shares the negative charge fairly. Resonance helps explain why molecules like the carbonate ion are more stable than they might appear if only one structure were possible.

Bicarbonate Ion

The bicarbonate ion, \(\mathrm{HCO}_{3}^{-}\), involves a slightly more complex structure compared to the carbonate ion. In addition to the central carbon and three oxygen arrangement, one of these oxygen atoms is also bonded to a hydrogen atom. This configuration brings about some distinct features:

• The hydrogen atom adds a layer of acidity to the bicarbonate ion.
• It retains a -1 overall charge.
• Two primary resonance structures are possible.

In a bicarbonate ion, one resonance structure will have a double bond between the carbon and one of the oxygen atoms, with that oxygen carrying a slight negative charge. The hydrogen is typically attached to a singly-bonded oxygen. In the alternate resonance structure, the location of the double bond shifts to the next oxygen, keeping the hydrogen attachment constant. This shifting of bonds in the resonance structures helps distribute the ion's charge, stabilizing it. Overall, this ability to resonate enhances the bicarbonate ion's reactivity and its role in buffering systems in nature.

Electron Distribution

Electron distribution in ions like carbonate and bicarbonate is dictated by their need to achieve a stable electronic configuration. In chemistry, resonance structures are a method to depict this as they indicate various plausible ways electrons can be organized within a molecule. This distribution is crucial because it affects the molecule's stability and reactivity.

• Electrons are always in motion, which is why one singular fixed structure cannot represent the real structure.
• In resonance, electrons are delocalized, meaning they are spread over a greater area than in a single bond.
• Delocalization leads to lower energy and increased stability of the molecule.

For the carbonate and bicarbonate ions, resonance is especially important. In carbonate \(\mathrm{CO}_{3}^{2-}\), each oxygen shares the negative charge equally over possible resonating structures. In bicarbonate \(\mathrm{HCO}_{3}^{-}\), resonance accounts for how the hydrogen attachment influences electron sharing among its components. Understanding electron distribution not only helps in depicting accurate molecular structures but also in predicting the chemical behavior of the molecules in reactions.