Problem 61 - Chemistry: An Atoms-Focused Approach

Question

Greenhouse Gases Chlorofluorocarbons (CFCs) are compounds linked to the depletion of stratospheric ozone. They are also greenhouse gases. Draw Lewis structures for the following CFCs: a. \(\overline{\mathrm{CCl}}_{3} \mathrm{F}\) (Freon 11 ) b. \(\left.\mathrm{CCl}_{2} \mathrm{F}_{2} \text { (Freon } 12\right)\) c. \(\mathrm{CClF}_{3}\) (Freon 13 ) d. \(\mathrm{Cl}_{2} \mathrm{FC}-\mathrm{CClF}_{2}\) (Freon 113 ) e. \(\left.\mathrm{ClF}_{2} \mathrm{C}-\mathrm{CClF}_{2} \text { (Freon } 114\right)\)

Step-by-Step Solution

Answer

Question: Draw the Lewis structures of the following chlorofluorocarbon (CFC) compounds: a. \(\overline{\mathrm{CCl}}_{3} \mathrm{F}\) b. \(\mathrm{CCl}_{2} \mathrm{F}_{2}\) c. \(\mathrm{CClF}_{3}\) d. \(\mathrm{Cl}_{2} \mathrm{FC}-\mathrm{CClF}_{2}\) e. \(\mathrm{ClF}_{2} \mathrm{C}-\mathrm{CClF}_{2}\)

Step 1: Count the valence electrons

For each compound, we'll first determine the total number of valence electrons by adding the valence electrons of each individual atom: a. \(\mathrm{CCl}_3 \mathrm{F}\): 4 (C) + 3x7 (Cl) + 7 (F) = 32 b. \(\mathrm{CCl}_{2} \mathrm{F}_{2}\): 4 (C) + 2x7 (Cl) + 2x7 (F) = 32 c. \(\mathrm{CClF}_{3}\): 4 (C) + 7 (Cl) + 3x7 (F) = 32 d. \(\mathrm{Cl}_{2} \mathrm{FC}-\mathrm{CClF}_{2}\): 2x7 (Cl) + 4 (C) + 7 (F) + 4 (C) + 7 (Cl) + 2x7 (F) = 66 e. \(\mathrm{ClF}_{2} \mathrm{C}-\mathrm{CClF}_{2}\): 7 (Cl) + 2x7 (F) + 4 (C) + 4 (C) + 7(C) + 2x7 (F) = 66

Step 2: Draw the skeleton structure

Place the least electronegative atom at the center and arrange the other atoms around it. a. C with three Cl atoms and one F atom b. C with two Cl atoms and two F atoms c. C with one Cl atom and three F atoms d. F atom between two Cl atoms and C-CClF2 chain e. FC-CClF2 and F atom near ClF2C

Step 3: Distribute the valence electrons

Start by placing pairs of electrons between atoms to form single bonds. Distribute the remaining electrons as nonbonding pairs to satisfy the octet rule: a. \(\mathrm{CCl}_3 \mathrm{F}\): [C-Cl] [Cl-C-Cl] [Cl-C-F] b. \(\mathrm{CCl}_{2} \mathrm{F}_{2}\): [C-Cl] [Cl-C-F] [C-F] c. \(\mathrm{CClF}_{3}\): [C-Cl] [C-F] [C-F] [C-F] d. \(\mathrm{Cl}_{2} \mathrm{FC}-\mathrm{CClF}_{2}\): [Cl-F-Cl]-[C-C]-[Cl-C]-[C-F]-[C-F] e. \(\mathrm{ClF}_{2} \mathrm{C}-\mathrm{CClF}_{2}\): [Cl-F-C-F]-[C-C]-[Cl-C]-[C-F]-[C-F]

Step 4: Check for formal charges

Verify that the formal charges on each atom are zero, or as close as possible to zero. The given structures are the correct Lewis structures as the formal charges of all atoms satisfy the octet rule, and the formal charges are minimized.

Key Concepts

Chlorofluorocarbons (CFCs)

Chlorofluorocarbons, or CFCs, are a group of organic compounds that contain carbon, chlorine, and fluorine atoms. These compounds were once widely used in applications like refrigeration, air conditioning, and spray propellants due to their non-flammable and stable nature.
However, their stability becomes an issue when they are released into the atmosphere, as they do not easily break down and can persist for many years. Once in the upper atmosphere, CFCs contribute significantly to environmental issues.
One major problem associated with CFCs is their ability to rise up to the stratosphere where they cause the depletion of the ozone layer. They have also been identified as potent greenhouse gases, contributing to global warming. Although their use has decreased significantly due to international agreements like the Montreal Protocol, understanding their chemical structure is crucial to understanding their environmental impact.

Valence Electrons

Valence electrons play a crucial role in the chemistry of atoms, as they determine how atoms will bond with each other to form compounds. They are the electrons in the outer shell of an atom.
For example, carbon has four valence electrons, while chlorine and fluorine each have seven. When we analyze the CFC compounds in the exercise, we count the valence electrons to predict how the atoms will bond and form molecules.
Lewis structures help visualize this by representing the valence electrons as dots around chemical symbols, showing how the electrons are shared between atoms to form covalent bonds. Identifying the number of valence electrons is a vital step in drawing Lewis structures accurately.

Ozone Depletion

Ozone depletion refers to the thinning of the Earth's ozone layer, located in the stratosphere. This layer acts as a shield, absorbing the majority of the Sun's harmful ultraviolet radiation.
CFCs are catalyzing this depletion process. Once released, they slowly migrate to the stratosphere, where they are broken down by UV light, releasing chlorine atoms.
These chlorine atoms then react with ozone molecules (\( \text{O}_3 \)) breaking them down into oxygen (\( \text{O}_2 \)) and perpetuating a cycle of ozone destruction. This loss can lead to higher levels of UV radiation reaching the Earth, increasing risks such as skin cancer and harming ecosystems.

Greenhouse Gases

Greenhouse gases absorb and emit radiation in the thermal infrared range, contributing to the greenhouse effect that warms the planet.
CFCs are considered a powerful class of greenhouse gases, even more effective than carbon dioxide when it comes to trapping heat within the Earth's atmosphere.
Though they exist in smaller quantities, the ability of CFCs to increase atmospheric temperatures significantly impacts climate patterns. Because of this potency, international efforts continue to phase out and reduce the presence of CFCs from industrial processes and products.