Question

Which of the following compounds or ions exhibit resonance? a. \(\mathrm{O}_{3}\) b. \(\mathrm{CNO}^{-}\) c. AsI \(_{3}\) d. \(\mathrm{CO}_{3}^{2-}\) e. AsF \(_{3}\)

Short answer

The compounds and ions that exhibit resonance are: a. \(\mathrm{O}_{3}\) b. \(\mathrm{CNO}^{-}\) d. \(\mathrm{CO}_{3}^{2-}\)

Step-by-step solution

Draw Lewis structures

First, we need to draw the Lewis structures of the given compounds/ions to determine if any of them exhibit resonance. If there are different possible arrangements of double or triple bonds, the structure exhibits resonance.

Analyze the Lewis structures for each compound/ions

a. \(\mathrm{O}_{3}\): Ozone has a central oxygen atom, with one double bond to another oxygen atom and one single bond to the third oxygen atom. There is also a non-bonding electron pair on the central oxygen atom. The electrons in the double bond can be shifted to form a new double bond with the single-bonded oxygen and change the existing double bond to a single bond. Therefore, ozone exhibits resonance. b. \(\mathrm{CNO}^{-}\): The cyanate ion has a carbon atom single-bonded to a nitrogen atom which is double-bonded to the oxygen atom. There is also a non-bonding electron pair on the nitrogen atom. The negative charge is delocalized among the 3 atoms, and the structure exhibits resonance as there can be arrangements in which the nitrogen is double-bonded to the carbon and single-bonded to the oxygen, with oxygen having a negative charge. c. AsI\(_{3}\): Arsenic triiodide has three arsenic-iodine single bonds, and each iodine atom has three lone pairs. There are no different possible arrangements of double or triple bonds and no delocalization of electrons. Therefore, AsI\(_{3}\) does not exhibit resonance. d. \(\mathrm{CO}_{3}^{2-}\): In carbonate ion, the carbon atom is double-bonded to one of the oxygen atoms and single-bonded to the other two oxygen atoms. Each oxygen atom also has two non-bonding electron pairs. Electrons from the double bond can be shifted to form a new double bond with one of the single-bonded oxygen atoms and change the existing double bond to a single bond. The negative charge is delocalized among the 3 oxygen atoms. Therefore, the carbonate ion exhibits resonance. e. AsF\(_{3}\): Arsenic trifluoride has three arsenic-fluorine single bonds, and each fluorine atom has three lone pairs. There are no different possible arrangements of double or triple bonds and no delocalization of electrons. Therefore, AsF\(_{3}\) does not exhibit resonance.

Identify compounds/ions that exhibit resonance

From the above analysis of the Lewis structures, we can conclude that: a. \(\mathrm{O}_{3}\) exhibits resonance. b. \(\mathrm{CNO}^{-}\) exhibits resonance. c. AsI\(_{3}\) does not exhibit resonance. d. \(\mathrm{CO}_{3}^{2-}\) exhibits resonance. e. AsF\(_{3}\) does not exhibit resonance.

Key concepts

Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms of a molecule, as well as any lone pairs of electrons that may exist. They help illustrate how atoms in a molecule are bonded together and the arrangement of electrons around atoms. To draw a Lewis structure:

• Count the total number of valence electrons available in the molecule or ion.
• Choose a central atom (usually the least electronegative apart from hydrogen) and connect other atoms to it using single bonds.
• Distribute the remaining electrons to complete the octet rule (or duet rule for hydrogen) for each atom.
• If there are not enough electrons to complete octets, double or triple bonds may be necessary.

Lewis structures are crucial in determining molecular geometry and evaluating if molecules exhibit resonance, as they show potential locations where double or triple bonds can form, leading to alternative structures.

Delocalization of Electrons

Delocalization of electrons occurs when electrons are shared among multiple atoms, rather than being confined between a single pair of atoms. This phenomenon is commonly seen in molecules or ions that exhibit resonance. In resonance structures:

• Electrons are not fixed in one position but can move or be 'delocalized' between several atoms.
• This delocalization stabilizes the molecule as the electrons occupy a larger space, lowering the energy of the molecule.
• For example, in the carbonate ion (\( \mathrm{CO}_3^{2-} \)), the extra electrons can hop between the oxygen atoms, compensating charges and alternating double bonds.

Resonance structures using the delocalization of electrons provide a more accurate depiction of molecules, offering insight into their stability and reactivity.

Chemical Compounds

Chemical compounds are substances composed of two or more different types of atoms bonded together through chemical bonds. These bonds can be ionic, formed by the complete transfer of electrons, or covalent, where atoms share electrons. Understanding how atoms in a compound share or exchange electrons is fundamental in chemistry.When studying compounds like ozone (\( \mathrm{O}_3 \)) or the carbonate ion (\( \mathrm{CO}_3^{2-} \)), it is crucial to recognize the role of resonance. Some compounds exhibit multiple structures where electrons can be arranged differently, achieving stability through resonance.In chemistry, recognizing compounds that can form these resonance structures is essential because:

• It influences the compound's reactivity and interaction with other molecules.
• Resonance impacts physical properties such as boiling and melting points.
• It provides a deeper understanding of the compound's overall strength and versatility.

Thus, chemical compounds are not just about their basic composition, but also about how their structure, represented by resonance, affects their chemical behavior.