Problem 81 - Chemistry: The Central Science in SI Units, Global Edition

Question

(a) What is a monomer? (b) Which of these molecules can be used as a monomer: ethanol, ethene (also called ethylene), methane?

Step-by-Step Solution

Answer

(a) A monomer is a small molecule that can chemically bond with other monomers to form a larger, more complex structure called a polymer. Examples of monomers include glucose, amino acids, and nucleotides. (b) Out of the given molecules - ethanol, ethene (ethylene), and methane - only ethene (ethylene) can be used as a monomer.

Step 1: (a) What is a monomer?

A monomer is a small molecule that can chemically bond with other monomers to form a larger, more complex structure called a polymer. Monomers possess the ability to form covalent bonds with other molecules, allowing them to combine and create a polymer chain. Examples of monomers include glucose, amino acids, and nucleotides.

Step 2: (b) Analyzing each molecule

Let's analyze each of the given molecules: 1. Ethanol: Its chemical formula is C2H5OH. Ethanol is a simple alcohol and does not possess the ability to form long chains or polymers. Therefore, it cannot be used as a monomer. 2. Ethene (Ethylene): Its chemical formula is C2H4. Ethene is an unsaturated hydrocarbon with a double bond between the two carbon atoms. The double bond can be broken to form a single bond and create a new bond with another ethene molecule. This process is known as polymerization, and ethene can be used as a monomer to form polyethylene. Hence, ethene (ethylene) can be used as a monomer. 3. Methane: Its chemical formula is CH4. Methane is a saturated hydrocarbon with no double or triple bonds, meaning it cannot easily form into long chains or polymers. As a result, it cannot be used as a monomer.

Step 3: Conclusion

Out of the given molecules - ethanol, ethene (ethylene), and methane - only ethene (ethylene) can be used as a monomer.

Key Concepts

Polymerization

Polymerization is a chemical process where small molecules, known as monomers, join together to form a larger molecule called a polymer. This transformation involves creating covalent bonds between the monomers.
During polymerization, these initial small units act like building blocks, linking consecutively to form long chains or networks.
Key features of polymerization include:

• The process can occur in various ways like addition polymerization or condensation polymerization.
• In addition polymerization, monomers join without losing any other molecules. This method is common with unsaturated monomers like ethene.
• Condensation polymerization involves monomers combining with the release of small molecules, such as water.

Polymers have a wide array of uses, from making plastic bags, which use polyethylene, to forming polyester materials in clothing. This flexible transformation of small molecules into large functional products highlights the importance of polymerization in both industrial and everyday contexts.

Ethene

Ethene, also known as ethylene, is a fundamental monomer in the polymer world. Its chemical formula is C\(_2\)H\(_4\), and it is an unsaturated hydrocarbon meaning it contains a double bond between its carbon atoms.
This double bond makes ethene highly reactive and suitable for polymerization processes.
Here's why ethene is special:

• It's a colorless gas with a faint sweet and musty odor.
• The double bond allows it to easily participate in addition polymerization, a process where numerous ethene molecules join to form polyethylene.
• Ethene’s reactive double bond can be broken and reformed with single bonds during reactions which allow it to interlink with other ethene molecules.

Ethene is vital in producing polyethylene, one of the most common plastics found in various products, from grocery bags to containers. Its versatility and reactivity make it indispensable in modern material science.

Chemical Bonds

Chemical bonds are the energetic glue holding the atoms in compounds together. They are crucial in determining how different substances form and react with each other. In the context of monomers and polymers, understanding how these bonds work is vital.
Types of chemical bonds include:

• Covalent bonds occur when two atoms share one or more pairs of electrons. This type is common in the formation of polymers, where monomers link together.
• Ionic bonds form when one atom donates an electron to another, creating charged ions that attract each other. These are typically found in salts rather than polymers.
• Hydrogen bonds, which are weaker interactions, often play roles in maintaining the structure of complex polymers like DNA.

The creation and breaking of chemical bonds dictate how monomers combine into polymers. For instance, in the polymerization of ethene, the double bonds between carbon atoms are broken to form single bonds, allowing each ethene molecule to connect into a long polyethylene chain. Understanding these interactions is key to manipulating materials for specific functions.