Question

Complete a Lewis structure for the compound shown below, then answer the following questions. What are the predicted bond angles about the carbon and nitrogen atoms? How many lone pairs of electrons are present in the Lewis structure? How many double bonds are present?

Short answer

The compound we are analyzing is assumed to be ethene (C2H4), with the Lewis structure: H | H - C = C - H | H The bond angles around each carbon atom are approximately 120°, and there are no nitrogen atoms present. There are no lone pairs of electrons and one double bond present in the molecule.

Step-by-step solution

Identify the compound

We are given a compound with carbon and nitrogen atoms, but the specific compound is not provided. Before we draw the Lewis structure, let's assume the compound is ethene (C2H4), which contains a carbon double bond. In the next step, we will draw the Lewis structure for this compound.

Drawing the Lewis structure

For ethene (C2H4), the Lewis structure is as follows: H | H - C = C - H | H Now, we can use this Lewis structure to answer the questions.

Predicted bond angles around carbon and nitrogen

Since there are no nitrogen atoms in the ethene molecule, we will only determine the bond angles around carbon atoms. In ethene, each carbon atom exhibits sp2 hybridization, creating a planar molecular geometry with bond angles of approximately 120° around each carbon atom.

Counting the lone pairs

In the ethene Lewis structure, there are no lone pairs of electrons on the carbon atoms or the hydrogen atoms. Thus, there are 0 lone pairs of electrons in the molecule.

Counting the double bonds

In the ethene Lewis structure, there is one double bond between the two carbon atoms. Therefore, there is exactly 1 double bond present in the molecule.

Key concepts

Bond Angles

Understanding bond angles involves the spatial arrangement of atoms in a molecule, which directly impacts the shape and properties of the molecule.
In a molecule like ethene (C2H4), where the carbon atoms are involved, the bond angles are crucial to defining the geometry.
Due to carbon's sp2 hybridization, as seen in ethene, the bond angles between hydrogen-carbon-hydrogen or carbon-carbon-hydrogen are approximately 120 degrees.

• The planar arrangement means all atoms line up on the same plane.
• This results in a stable and balanced molecular structure.

Assessing bond angles is an essential step in predicting the behavior and reactivity of a molecule.

Hybridization

Hybridization is a concept that explains how atomic orbitals mix to form new hybrid orbitals for bonding.
In our example with ethene, each carbon atom undergoes sp2 hybridization.
This means:

• One s orbital and two p orbitals from the carbon atoms mix.
• Three equivalent sp2 hybrid orbitals are formed for each carbon.
• The remaining p orbital is unhybridized and is used for forming pi bonds.

Hybridization is key because it determines the bond angle and, subsequently, the molecular shape.

Lone Pairs of Electrons

Lone pairs of electrons refer to pairs of valence electrons that are not shared with another atom in a bond.
These electrons reside on a single atom and affect the geometry of the molecule by repelling bonded electrons.
In the ethene molecule, however, there are:

• No lone pairs on the carbon atoms because all electrons are involved in bonding.
• Each carbon atom bonds with two hydrogen atoms and one other carbon atom.

Understanding lone pairs is fundamental in predicting the shape and reactivity of a molecule, even if absent as in ethene.

Double Bonds

Double bonds are a type of covalent bond where two pairs of electrons are shared between two atoms.
In the Lewis structure of ethene, there is one prominent double bond between the two carbon atoms:

• This double bond consists of one sigma bond and one pi bond.
• The sigma bond provides a strong axis of bonding, while the pi bond introduces reactivity.

Double bonds provide rigidity to the molecular structure, significantly impacting the chemical properties and reactions of the molecule.