Question

The free radical \(\mathrm{CF}_{3} \mathrm{O} \cdot\) is produced during the decomposition of HFC-134a. a. Propose a Lewis structure for this free radical. b. Offer a possible reason why \(\mathrm{CF}_{3} \mathrm{O} \cdot\) does not cause ozone depletion.

Short answer

a. The structure is (\(\mathrm{CF}_3\) bonded to \(\mathrm{O}\) with an unpaired electron on \(\mathrm{O}\)). b. It does not contain chlorine, avoiding ozone-destroying reactions.

Step-by-step solution

Understanding the Lewis Structure

A Lewis structure represents the arrangement of electrons among the atoms of a molecule. In the molecule \(\mathrm{CF}_3\mathrm{O}\cdot\), carbon (C) is bonded to three fluorine (F) atoms and one oxygen atom, while the oxygen atom has an unpaired electron (making it a free radical). We must arrange these atoms to reflect their valence electrons.

Drawing the Lewis Structure

Carbon has 4 valence electrons, each fluorine has 7, and oxygen has 6, totaling up to \(4 + (3 \times 7) + 6 = 31\) electrons. Normally, fluorine atoms will each form one bond to the carbon atom, using one electron from carbon and one from each fluorine. The remaining unpaired electron is located on the oxygen atom, resulting in the structure:- C atom in the center, sharing one bond with each F,- O atom bonded to C, and with one free electron (free radical).

Rationalizing Non-involvement in Ozone Depletion

The structure of \(\mathrm{CF}_3\mathrm{O}\cdot\) significantly influences its reactivity. Unlike CFCs, which release chlorine atoms that catalyze the breakdown of ozone, \(\mathrm{CF}_3\mathrm{O}\cdot\) does not contain chlorine and does not release any other reactive halogen atoms under typical atmospheric conditions. Thus, it lacks the ability to catalyze ozone decomposition.

Key concepts

Free Radical

In chemistry, a free radical is an atom or molecule that contains an unpaired electron. This unpaired electron makes the radical highly reactive because atoms and molecules tend to seek stability. Stability is often achieved by pairing all of their electrons. Free radicals are incredibly important in many chemical processes. One common example involves their role in oxidation reactions, where they can act as intermediates. When considering the molecule CF₃O· (trifluoromethoxy), the unpaired electron is located on the oxygen atom. This makes CF₃O· a free radical. Free radicals tend to react with other molecules to pair up their unpaired electron, which can initiate chain reactions. Understanding the behavior and characteristics of free radicals allows scientists to predict how certain substances will interact under various conditions.

Ozone Depletion

Ozone depletion refers to the thinning of the Earth's ozone layer, primarily caused by chemical reactions with certain pollutants. The ozone layer, located in the Earth's stratosphere, plays a crucial role in absorbing and blocking the majority of the sun's harmful ultraviolet radiation. The depletion primarily occurs due to the presence of halogenated compounds, particularly chlorofluorocarbons (CFCs). When these compounds break down under ultraviolet light, they release chlorine atoms.

• Chlorine atoms are highly reactive and can destroy ozone molecules.
• One chlorine atom has the potential to break down thousands of ozone molecules during its presence in the stratosphere.

This destructive process leads to reduced ozone concentration, increasing the risk of exposure to harmful UV rays, which can cause problems like increased skin cancer rates and environmental damage.

Valence Electrons

Valence electrons are the outermost electrons of an atom and are crucial in determining how the atom interacts and bonds with others. These electrons dictate the chemical reactivity and bonding capabilities of the element. In the context of the Lewis structure for CF₃O·, understanding valence electrons helps in constructing the model of the molecule:

• Carbon (C) has 4 valence electrons.
• Each Fluorine (F) atom has 7 valence electrons.
• Oxygen (O) has 6 valence electrons.

Together, the molecule accumulates a total of 31 valence electrons. In drawing the Lewis structure: - Carbon forms a single bond with each of the three fluorine atoms. - The oxygen atom bonds to carbon and retains the unpaired electron, identifying it as a free radical. Learning about valence electrons is fundamental to understanding molecular structures and predicting chemical behavior.

CFCs

Chlorofluorocarbons (CFCs) are synthetic compounds made up of carbon, chlorine, and fluorine. They were once widely used in refrigeration, air conditioning, and as propellants in aerosol sprays. CFCs gained attention due to their impact on the ozone layer. When released into the atmosphere, they are stable at lower altitudes but eventually make their way to the stratosphere, where ultraviolet light breaks them down to release chlorine.

• Chlorine atoms then react with ozone molecules, catalyzing their destruction.
• This process results in significant ozone layer depletion, increasing the penetration of ultraviolet rays.

Due to their role in environmental harm, CFCs are now largely regulated or banned under policies such as the Montreal Protocol. Understanding CFCs has led to finding alternative substances and technologies to reduce atmospheric damage.