Question

Predict the geometry of nitrous oxide \(\left(\mathrm{N}_{2} \mathrm{O}\right),\) by the VSEPR method, and draw resonance structures for the molecule. (Hint: The atoms are arranged as NNO.)

Short answer

The geometry of NNO is linear, and its resonance structures are: \(:\overset{+}{\text{N}} \equiv \text{N} - \overset{-}{\text{O}} :, :\text{N} =\overset{+}{\text{N}}=\overset{-}{\text{O}} :\).

Step-by-step solution

Determine the Total Number of Valence Electrons

Each nitrogen atom (N) has 5 valence electrons, and oxygen (O) has 6 valence electrons. Thus, the total number of valence electrons for NNO is calculated as follows:\[\text{Total valence electrons} = 5 \times 2 + 6 = 16\]

Choose the Central Atom and Draw a Skeleton Structure

Arrange the atoms with nitrogen (N) in the center since it is less electronegative than oxygen (O). The skeleton structure is N—N—O.

Calculate and Distribute Electron Pairs

With 16 valence electrons, we calculate pairs: \(16/2=8\) pairs. Initially, distribute the pairs as bonding pairs between each atom in the skeleton structure:1. Use 2 pairs (4 electrons) to form 2 single bonds.2. Distribute 6 pairs (12 electrons) as lone pairs: 3 pairs around the terminal N and O (considering octet rule).

Assign Remaining Electrons and Optimize Structure

Consider multiple bonds if there are any remaining electrons or if terminal atoms lack a full octet. Adjust bonds so that each atom achieves a complete octet. Add double or triple bonds as necessary. One satisfactory structure could be: \[ \text{N} \equiv \text{N} - \text{O} \]

Draw Resonance Structures

Draw resonance structures by relocating electron pairs. For nitrous oxide, resonance structures include:1. \[ :\overset{+}{\text{N}} \equiv \text{N} - \overset{-}{\text{O}} : \]2. \[ :\text{N} =\overset{+}{\text{N}}=\overset{-}{\text{O}} :\]

Predict the Molecular Geometry Using VSEPR

The central nitrogen in NNO has one region of electron density due to the triple bond with the terminal nitrogen and a lone pair, totaling 2 steric regions. According to VSEPR, this forms a linear geometry for the molecule.

Key concepts

Molecular Geometry

Molecular geometry is a concept that describes the shape of a molecule. It is determined mainly by the number of electron pairs around the central atom, as explained by the VSEPR theory. In the VSEPR (Valence Shell Electron Pair Repulsion) method, electron pairs, which include both bonding and lone pairs, are arranged as far apart as possible to minimize repulsion.
For nitrous oxide ( \( ext{N}_2 ext{O} \)), the central nitrogen atom is bonded through a triple bond with one terminal nitrogen and a single bond with oxygen. This structure implies that the molecule has linear geometry.

• The theory helps predict that the bonding pairs will form a straight line.
• Linear geometry means that the angle between the bonded atoms is 180°.

Understanding the geometry is crucial as it affects the molecule's physical and chemical properties, such as polarity and reactivity.

Valence Electrons

Valence electrons are the electrons found in the outermost shell of an atom. These electrons play a key role in chemical bonding and reactions. In the example of nitrous oxide ( \( ext{N}_2 ext{O} \)), calculating valence electrons is the first step in predicting the molecule's structure and properties.

• Nitrogen ( \( ext{N} \)) has 5 valence electrons each.
• Oxygen ( \( ext{O} \)) has 6 valence electrons.

When combined, nitrous oxide has a total of 16 valence electrons: \[2(5) + 6 = 16\]Calculating these electrons helps in determining how atoms bond together and whether single, double, or triple bonds are formed. Correct distribution according to these rules gives each atom a stable configuration, following the octet rule.

Resonance Structures

Resonance structures are a way to illustrate the multiple ways electrons can be arranged in a molecule, without changing the actual positions of atoms. These structures are significant because electrons are delocalized across different bonds, impacting the molecule's stability and properties.
For nitrous oxide ( \( ext{N}_2 ext{O} \)), there are several possible resonance structures, showing different electron pair positions:

• A structure with a triple bond between the nitrogen atoms and a single bond to oxygen: \( : ext{N} riplebond ext{N} ext{-} ext{O}: \)
• Another form where there are double bonds between each pair of internal and terminal atoms: \( : ext{N} ext{=} ext{N} ext{=} ext{O} \)

These diagrams reflect the electron distribution more accurately than any single Lewis structure. Keeping electrons mobile offers insight into the molecule's behavior in reactions and its energy state.

Octet Rule

The octet rule is an essential principle in chemistry for understanding the way atoms tend to bond. It states that atoms are generally most stable when they have eight electrons in their valence shell, resembling the electron configuration of noble gases.

• In the case of nitrous oxide ( \( ext{N}_2 ext{O} \)), achieving a stable electron configuration is a priority when forming bonds.
• The nitrogen atoms try to share or gain electrons such that they have a total of eight electrons in their outer shell.

This can result in the formation of double or triple bonds to satisfy the octet rule. Some readings of structures allow resonance, as in \( ext{N}_2 ext{O} \), indicating flexibility in achieving a stable configuration. The fulfillment of the octet rule ensures molecules are chemically stable and less likely to react further unless energy is introduced into the system. Understanding this rule is vital when predicting molecular reactions and properties.