Question

Draw Lewis structures for the following organic molecules: (a) tetrafluoroethylene \(\left(\mathrm{C}_{2} \mathrm{~F}_{4}\right),(\mathrm{b})\) propane \(\left(\mathrm{C}_{3} \mathrm{H}_{8}\right),(\mathrm{c})\) butadiene \(\left(\mathrm{CH}_{2} \mathrm{CHCHCH}_{2}\right),(\mathrm{d})\) propyne \(\left(\mathrm{CH}_{3} \mathrm{CCH}\right),\) (e) benzoic acid \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\right)\). (To draw \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH},\) replace an \(\mathrm{H}\) atom in benzene with a COOH group.)

Short answer

Draw Lewis structures completing the octet for (a) C2F4: C=C with two F on each C; (b) C3H8: C-C-C with hydrogens completing octets; (c) CH2CHCHCH2: C=C-C=C with hydrogens; (d) CH3CCH: CH3-C≡C-H; (e) C6H5COOH: Benzene ring with COOH replacing one H.

Step-by-step solution

Understanding Tetrafluoroethylene (C2F4)

Tetrafluoroethylene has two carbon atoms connected by a double bond and each carbon is bonded to two fluorine atoms. Each fluorine atom forms a single bond with carbon, having three lone pairs around it.

Drawing Lewis Structure of Tetrafluoroethylene

1. Draw a C=C double bond. 2. Connect each carbon to two fluorine atoms. 3. Complete the octet by adding three lone pairs on each fluorine atom.

Understanding Propane (C3H8)

Propane consists of three carbon atoms single bonded in a chain (C-C-C), with each carbon having enough hydrogens to complete its octet.

Drawing Lewis Structure of Propane

1. Draw a chain of three carbon atoms with single bonds. 2. Connect enough hydrogen atoms to ensure each carbon has four bonds in total.

Understanding Butadiene (CH2CHCHCH2)

Butadiene contains four carbon atoms with alternating single and double bonds. The two end carbons are each bonded to two hydrogen atoms.

Drawing Lewis Structure of Butadiene

1. Arrange the carbon atoms in a chain: C=C-C=C. 2. Attach the hydrogen atoms: H2C=CH-CH=CH2. 3. Ensure each atom achieves an octet by adjusting bonds as needed.

Understanding Propyne (CH3CCH)

Propyne has three carbon atoms: the first carbon is bonded to three hydrogens, the second carbon is connected to the first with a single bond, and to the third with a triple bond.

Drawing Lewis Structure of Propyne

1. Begin with CH3 connected to C by a single bond. 2. Connect the second carbon to the third carbon with a triple bond. 3. Attach hydrogens to complete the octets as necessary.

Understanding Benzoic Acid (C6H5COOH)

Benzoic acid includes a benzene ring with a carboxylic acid group (COOH) replacing one hydrogen. Benzene is a six-carbon ring with alternating double bonds.

Drawing Lewis Structure of Benzoic Acid

1. Draw the benzene ring with alternating C=C and C-C bonds. 2. Replace one hydrogen with the COOH group. 3. Draw the COOH group: connect C to -OH and C=O, and ensure all atoms have full octets.

Key concepts

Organic molecules

Organic molecules are primarily composed of carbon atoms bonded together in various ways, often along with hydrogen, oxygen, nitrogen, sulfur, and other elements. These molecules are the basis of all known life on Earth. They form the structures, functions, and information-carrying systems of cells and organisms.
Understanding organic molecules is essential in fields like biochemistry, medicine, and materials science.

• They can be simple, such as methane (CH₄), or complex like DNA or proteins.
• Carbon's ability to form four bonds with other atoms, including other carbon atoms, allows for the diversity and complexity of organic molecules.
• These molecules often follow basic structural patterns, which include chains, rings, or a combination of both.

In the provided exercise, molecules like propane, butadiene, and benzoic acid demonstrate common organic structures. Examining these structures helps us understand how organic molecules behave and react.

Chemical bonding

Chemical bonding is the process that allows atoms to form molecules and compounds by sharing or transferring electrons. The two primary types are covalent bonds, where electrons are shared between atoms, and ionic bonds, where electrons are transferred to achieve stability.
Chemical bonds hold the molecules together and establish the properties of substances.

• Covalent bonds are most prevalent in organic molecules, as seen in the carbon-carbon and carbon-hydrogen bonds.
• Single, double, and triple covalent bonds exist, with double and triple bonds representing stronger interactions due to shared electrons.
• In the exercise, different bonds such as the double bonds in tetrafluoroethylene and butadiene, and the triple bond in propyne, highlight the variety of chemical bonding.

Understanding how atoms bond in molecules provides insights into their structure, stability, and the way they react with other substances.

Octet rule

The octet rule is a chemical principle that asserts that atoms are most stable when they have eight electrons in their valence shell. This configuration resembles the electron configuration of noble gases, which are inherently stable and unreactive.
This principle guides the formation of chemical bonds in many elements, especially in organic chemistry.

• Atoms like carbon, oxygen, and nitrogen frequently follow the octet rule by sharing electrons through covalent bonds.
• In the exercise, ensuring that each element in the molecules like propane and butadiene achieves an octet is a crucial step in drawing correct Lewis structures.
• However, it’s worth noting that some elements can violate the octet rule, like in the case of compounds containing elements from the third period or beyond.

The octet rule is a foundational concept in understanding how and why atoms bond to form stable molecules.

Benzene structure

The benzene structure is a classic example of a stable and unique molecular structure due to its conjugated system of alternating single and double bonds. Benzene is a six-carbon ring with the formula C₆H₆ and is the simplest aromatic hydrocarbon.
Its structure is symbolized by a hexagon with alternating lines or a circle inside to indicate delocalized electrons.

• Benzene’s bonds are identical in length, a characteristic feature of its stability, due to the resonance that distributes electrons across the ring.
• The exercise highlights benzene within benzoic acid, where its stable framework allows for substitution without losing its aromatic property.
• Understanding benzene’s structure is crucial in organic chemistry as it serves as a fundamental building block in many aromatic compounds.

The special stability of benzene arises from its resonance and the equal sharing of electron density, making it one of the most studied molecules in chemical science.