Question

Draw Lewis structures for these organic molecules, in each of which there is one \(\mathrm{C}=\mathrm{C}\) bond and the rest of the carbon atoms are joined by \(\mathrm{C}-\mathrm{C}\) bonds: \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{~F}, \mathrm{C}_{3} \mathrm{H}_{6}, \mathrm{C}_{4} \mathrm{H}_{8}\).

Short answer

The Lewis structures for the given organic molecules, showing exactly one carbon-carbon double bond (\(\mathrm{C}=\mathrm{C}\)) in each molecule are: For \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{~F}\), it's F-C=C-H with the double bond between the two carbons and two H atoms bonded to the second carbon. For \(\mathrm{C}_{3} \mathrm{H}_{6}\), it's C=C-C with two H atoms bonded to each carbon. For \(\mathrm{C}_{4} \mathrm{H}_{8}\), it's C-C=C-C with three H atoms bonded to the first and fourth carbons, and one H atom bonded to the second and third carbons.

Step-by-step solution

Draw Lewis Structure for \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{~F}\)

Each carbon (C) atom can form 4 bonds, each hydrogen (H) atom forms 1 bond, and fluorine (F) forms 1 bond. First, draw two carbon atoms connected by a double bond to account for the \(\mathrm{C}=\mathrm{C}\) requirement. Arrange the 1 F and 3 H atoms around the carbon atoms to ensure the octet rule is satisfied. The Lewis structure can be represented as: F-C=C-H with two H atoms bonded to the second carbon.

Draw Lewis Structure for \(\mathrm{C}_{3} \mathrm{H}_{6}\)

In this case, given there are 3 carbon atoms and 6 hydrogen atoms, connect the 3 carbon atoms together with one double bond and one single bond to satisfy the \(\mathrm{C}=\mathrm{C}\) requirement. Then, distribute the 6 H atoms around the 3 carbon atoms to satisfy the octet rule. The Lewis structure can be represented as: C=C-C, with the first two carbon atoms each having two H atoms bonded to them, and the third carbon atom having two H atoms bonded to it.

Draw Lewis Structure for \(\mathrm{C}_{4} \mathrm{H}_{8}\)

For \(\mathrm{C}_{4} \mathrm{H}_{8}\), connect the 4 carbon atoms in a chain with one double bond and two single bonds to account for the \(\mathrm{C}=\mathrm{C}\) requirement. Then, distribute the 8 hydrogen atoms around the 4 carbon atoms to satisfy the octet rule. The Lewis structure can be represented as: C-C=C-C, with the first and last carbon atoms each having three H atoms bonded to them, and the second and third carbon atoms each having one H atom bonded to them.

Key concepts

Organic Molecules

Organic molecules are the backbone of life on Earth, primarily composed of carbon atoms. The versatility of carbon allows it to form stable bonds with many elements, including itself. This results in a diverse range of organic molecules. Carbon can form both chains and rings, leading to complex structures with various functional groups.
Organic chemistry focuses on these carbon-based molecules and their interactions. Simple organic compounds, such as hydrocarbons like ethylene (\(\mathrm{C}_2\mathrm{H}_4\)), contain only carbon and hydrogen. However, more complex molecules can also have oxygen, nitrogen, sulfur, and halogens like fluorine.
Understanding the structure and behavior of organic molecules is essential in fields such as medicine, biochemistry, and environmental science. The structure can influence properties like boiling point, solubility, and reactivity, which are crucial for practical applications in these fields.

• Carbon’s ability to form four covalent bonds is key to the diversity of organic compounds.
• Functional groups such as alcohols, ketones, and halides introduce reactive sites into organic molecules.
• The study of how organic molecules interact is pivotal for innovations in pharmaceuticals, agricultural chemicals, and materials science.

Carbon-Carbon Double Bond

Carbon-carbon double bonds (\(\mathrm{C} = \mathrm{C}\)) are a fundamental feature in organic chemistry. They occur when two carbon atoms share two pairs of electrons, creating a stronger and shorter bond compared to a single bond. These double bonds are found in a variety of compounds, such as alkenes, which are hydrocarbons containing at least one double bond.
Double bonds significantly influence the geometry and reactivity of a molecule. They are planar, meaning all atoms involved are in the same plane, which affects molecule shape and function. For instance, the double bond in alkenes introduces geometric isomerism, leading to cis and trans configurations.
Reactivity is another key feature of carbon-carbon double bonds. They are more reactive than single bonds due to the greater energy of the pi-bond, making them key sites for chemical reactions such as addition reactions. This reactivity is exploited in polymerization processes, where small molecules (monomers) are chemically bonded to form long chains called polymers.

• A \(\mathrm{C}=\mathrm{C}\) double bond is characterized by its stronger and shorter bond compared to single bonds.
• The planar structure of double bonds can lead to different isomers, affecting molecular properties and functions.
• Double bonds are reactive and play crucial roles in fundamental chemical processes like polymerization.

Octet Rule

The octet rule is a guiding principle in chemistry that explains bonding behavior in many molecules. It states that atoms tend to form bonds until they are surrounded by eight electrons, replicating the electron configuration of the noble gases. This "full outer shell" can be achieved through sharing, donating, or accepting electrons.
In Lewis structures, the octet rule helps predict molecule stability and structure. For example, in organic molecules, carbon achieves an octet by sharing its four electrons to form four covalent bonds, either as single, double, or even triple bonds.
This rule, however, is not without exceptions. Elements in the third period and beyond can exceed the octet due to available d-orbitals, allowing expanded octets. Additionally, some molecules, like radicals, may have less than eight electrons around an atom.

• The octet rule helps determine the stability of molecules by achieving a noble gas electron configuration.
• Carbon follows the octet rule by forming up to four covalent bonds to achieve eight valence electrons.
• There are exceptions to the octet rule, mainly involving elements that can utilize d-orbitals or molecules with unpaired electrons.