Problem 77 - Chemistry: The Central Science

Question

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

Step-by-Step Solution

Answer

(a) A monomer is a small molecule or compound that can bind chemically with other molecules to form a larger macromolecule, known as a polymer. Monomers have at least one bond that can be broken and reformed as part of the polymerization process. (b) Among benzene, ethene, and methane, only ethene can be used as a monomer. Benzene is relatively stable and does not participate in polymerization reactions, while methane is unreactive and incapable of forming a polymer. Ethene, an unsaturated hydrocarbon with a double bond, can undergo polymerization to produce polyethylene polymer.

Step 1: (a) Definition of a Monomer

A monomer is a small molecule or compound that can bind chemically with other molecules to form a larger macromolecule, known as a polymer. Monomers have at least one bond that can be broken and reformed as part of the polymerization process. The process of combining monomers to form a polymer is called polymerization.

Step 2: (b) Identifying Monomers Among the Given Molecules

To determine which of the given molecules (benzene, ethene, and methane) can be used as a monomer, we need to examine their chemical structures and identify if any of them have the necessary bonding capabilities to form a polymer. 1. Benzene: Benzene has the molecular formula C6H6. It is an aromatic, cyclic hydrocarbon with alternating single and double bonds in its ring structure. Benzene is relatively stable and generally does not participate in polymerization reactions. Hence, benzene cannot be used as a monomer. 2. Ethene (ethylene): Ethene has the molecular formula C2H4. It is an unsaturated hydrocarbon with a double bond between the two carbon atoms. This double bond can be broken to form single bonds, allowing ethene to react with other molecules and undergo polymerization. Ethene is a common monomer used to produce polyethylene polymer. Therefore, ethene can be used as a monomer. 3. Methane: Methane has the molecular formula CH4. It is a saturated hydrocarbon with all single bonds, which makes it relatively unreactive. Methane is not capable of forming a polymer and cannot be used as a monomer. In conclusion, among benzene, ethene, and methane, only ethene can be used as a monomer.

Key Concepts

Understanding Polymerization

Polymerization is the fascinating process where small molecules, called monomers, come together to form larger structures known as polymers. This transformation involves chemical reactions where monomers link up in long, repeating chains or in complex three-dimensional networks.
There are two primary types of polymerization:

• Addition Polymerization: In this process, monomers add to each other without the loss of any small molecules. Ethylene polymerizes this way to create polyethylene.
• Condensation Polymerization: This involves the joining of monomers with the loss of small molecules like water.

Polymerization is crucial in creating materials that we rely on every day, from plastics and fibers to high-tech materials used in aerospace and medicine. Understanding this is key to grasping how materials are engineered and highlights the versatility and importance of chemistry in innovation.

The Role of Ethylene in Polymer Production

Ethylene, also known as ethene, is a powerhouse in the world of monomers. With the chemical formula C2H4, ethylene is the simplest alkene and features a crucial double bond between its two carbon atoms.
This double bond is reactive, making it ideal for polymerization. Ethylene is used extensively to create one of the most common polymers, polyethylene. Polyethylene is a plastic found in many everyday objects such as plastic bags, bottles, and even piping.
When ethylene undergoes polymerization, the double bonds open up, allowing chains of ethylene units to connect. This creates long strands that result in the durable and flexible properties of polyethylene.

• Ethylene's simplicity and reactivity make it an ideal monomer.
• The production process is efficient and cost-effective.
• It's pivotal for creating products that contribute to modern life.

Exploring Chemical Bonding in Monomers

Chemical bonding is fundamental to understanding how monomers turn into polymers. Bonds are the forces holding atoms together, and the type and nature of these bonds determine a molecule's properties and reactivity.
In monomers like ethylene, we rely on its carbon-carbon double bond. This bond is a type of covalent bond formed by the sharing of electron pairs between atoms. The double bond in ethylene is particularly reactive, which is why it is so useful in polymerization.
Key Types of Chemical Bonds:

• Covalent Bonds: Strong bonds where atoms share electrons. Seen in the primary structure of many monomers.
• Double Bonds: A type of covalent bond involving two shared pairs of electrons. It’s the reactivity of these bonds in ethylene that enable polymerization into polyethylene.

Understanding these bonds helps us design and synthesize new materials, pushing forward the boundaries of material science and engineering.