Problem 2 - Chemistry: The Central Science in SI Units, Global Edition

Question

Molecules in the upper atmosphere tend to contain double and triple bonds rather than single bonds. Suggest an explanation. [Section 18.1]

Step-by-Step Solution

Answer

In conclusion, molecules with double and triple bonds are more prevalent in the upper atmosphere due to their increased stability and strength. These characteristics make them less reactive and more resistant to the harsh conditions in the upper atmosphere, such as intense radiation, low temperatures, and low pressure. This gives multiple-bonded molecules a better chance to exist in such challenging environments compared to molecules with single bonds, which are typically more prone to reactions and less stable.

Step 1: Understand Bond Characteristics

Single bonds involve one pair of shared electrons between atoms, while double and triple bonds involve two or three electron pairs, respectively. Typically, multiple bonds (double and triple) are shorter, stronger, and more energy-stable compared to single bonds. This difference has implications on the reactivity and stability of molecules.

Step 2: Consider the Upper Atmosphere's Environment

The upper atmosphere faces conditions such as intense UV radiation, extremely low temperatures, and low pressure, making it a challenging environment for molecules to exist. Consequently, molecules with greater stability and resistance to these harsh conditions have a better chance of existing in the upper atmosphere.

Step 3: Relate Bond Types to the Environment

Due to their increased stability and strength, molecules with double and triple bonds are generally less reactive and more resistant to the intense conditions found in the upper atmosphere, such as high-energy radiation. As a result, they are more likely to be prevalent in the upper atmosphere than molecules with single bonds, which are typically more prone to reactions and less stable.

Step 4: Conclude the Explanation

In conclusion, molecules in the upper atmosphere tend to contain double and triple bonds, rather than single bonds, because multiple bonds provide greater stability and resistance to the harsh conditions of the upper atmosphere, such as intense radiation, low temperatures, and low pressure. These characteristics make multiple-bonded molecules more suitable for survival in the extreme environment of the upper atmosphere.

Key Concepts

Understanding the Upper Atmosphere

The upper atmosphere is a region of Earth's atmosphere that lies above the troposphere, extending from around 6 miles to hundreds of miles above the surface. It includes the stratosphere, mesosphere, thermosphere, and exosphere. Each of these layers has unique characteristics, such as variations in temperature, pressure, and composition.
Conditions in the upper atmosphere are quite different from those at the Earth's surface.

• Temperatures can range from extremely cold to very hot.
• Pressure is significantly lower than at ground level.
• It is an area where high-energy ultraviolet (UV) radiation is particularly intense.

Molecules present in this part of the atmosphere must be able to endure these harsh environmental conditions. They need to be stable enough to resist being broken apart by the energetic UV rays and the lower pressure that is prevalent at such high altitudes.

Molecular Stability in the Upper Atmosphere

Molecular stability refers to the ability of molecules to remain intact and resist breaking apart under various environmental conditions. In the upper atmosphere, where UV radiation is abundant and pressure is low, stability becomes a critical factor for molecular survival.
Molecules with double and triple bonds offer greater stability compared to those with single bonds.

• Double bonds involve two shared pairs of electrons, providing greater strength to the molecule's structure.
• Triple bonds involve three shared pairs of electrons, making them even stronger and more stable.

This increased stability means molecules are less reactive and more able to resist the disruptive conditions of the upper atmosphere, where less stable molecules might disintegrate or react easily.

Impact of UV Radiation

Ultraviolet (UV) radiation consists of high-energy light waves that can have significant effects on molecules, making UV radiation a crucial factor in understanding molecular stability in the upper atmosphere.
UV radiation has enough energy to break chemical bonds in molecules, leading to potential destruction or alteration of the molecular structure. Molecules in environments exposed to intense UV must therefore be strong enough to withstand its effects.

• Single bonds can be broken more easily by UV radiation due to their generally lower bond strength.
• Double and triple bonds have higher bond energies, providing resistance against UV-induced breaking.

Because molecules in the upper atmosphere are constantly bombarded by UV radiation, those with stronger bonds, like double and triple bonds, are far better equipped to survive these conditions.

The Importance of Bond Strength

Bond strength is a key factor in determining the durability and stability of a molecule. In a chemical bond, it is the force needed to hold atoms together, and it varies across single, double, and triple bonds.
Stronger bonds imply higher stability, as more energy is required to break them.

• Single bonds involve one pair of electrons and are the weakest type of bond.
• Double bonds share two pairs of electrons, which increases the bond strength considerably.
• Triple bonds, sharing three pairs of electrons, are the strongest and most stable.

In the harsh conditions of the upper atmosphere, molecules with stronger bonds like double and triple bonds are preferable as they provide greater resistance to destruction by environmental factors.
Their enhanced bond strength makes them better suited to withstand the intense UV radiation and extreme temperatures found at such altitudes.