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Chapter 12: Problem 81

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

Short Answer

Expert verified
A monomer is a molecule that can form polymers. Ethene can be used as a monomer, but ethanol and methane cannot.

Step by step solution

01

Understanding Monomers

A monomer is a small molecule that can join together with other similar molecules to form a large chain or a complex molecule, known as a polymer. Monomers must have the ability to form at least two chemical bonds to link with other monomers.
02

Assessing Ethanol as a Monomer

Ethanol (C2H5OH) is an alcohol with two carbon atoms. Its structure does not allow it to form chains by linking with other ethanol molecules through chemical bonds typical of polymer formation. Therefore, it cannot act as a monomer.
03

Assessing Ethene as a Monomer

Ethene (C2H4) is an alkene with a double bond between its carbon atoms. This double bond allows ethene molecules to polymerize by opening up to form longer chains. Therefore, ethene can act as a monomer, commonly used in forming polyethylene.
04

Assessing Methane as a Monomer

Methane (CH4) has a tetrahedral structure with a single carbon atom bonded to four hydrogen atoms. It cannot form polymers since it lacks the reactive sites needed to bond with other methane molecules. Therefore, methane cannot be used as a monomer.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Polymerization
Polymerization is a chemical process that transforms monomers into polymers by linking them through various types of bonds. Consider it like connecting building blocks to create a long chain. Here鈥檚 how it all works:
  • Chain-growth polymerization: This type begins with a reactive monomer with a double bond, like ethylene. In a reaction called a free radical reaction, the double bond opens, allowing each ethylene unit to connect sequentially.
  • Step-growth polymerization: In this process, monomer units with multiple reactive sites come together, forming bonds in a stepwise fashion. Typically seen in the creation of polyesters and polyamides.
During polymerization, it鈥檚 crucial to have reactive sites enabled to form a continuous chain of monomers, leading to the formation of a stable and durable polymer.
Ethylene
Ethylene, also known as ethene, is a vital hydrocarbon in the polymer industry. It is a colorless gas with the formula C2H4 and is characterized by a double bond between the two carbon atoms. This double bond is crucial because:
  • It allows ethylene to participate in polymerization by opening up, making it highly reactive.
  • Whenever the bond opens, it provides the opportunity to connect with other ethylene molecules, forming a chain.
Ethylene is notable for its role in producing polyethylene, which is the most common plastic worldwide. It鈥檚 lightweight, durable, and applicable in numerous products from grocery bags to containers.
Chemical Bonding
Chemical bonding is the force that holds atoms together within a molecule. In the context of polymerization, these bonds are crucial for joining monomers:
  • Covalent bonds: These are the strongest type of bonds, formed by the sharing of electrons between atoms. They provide stability in polymer chains.
  • Double bonds: Found in alkenes like ethylene, these involve the sharing of two pairs of electrons, making them especially important for initiating polymerization reactions.
Chemical bonding allows monomers like ethene to connect and generate polymers such as polyethylene, ensuring a stable and durable material structure.
Polyethylene
Polyethylene is a polymer made from the polymerization of ethylene molecules. This material is versatile and widely used in everyday items:
  • Known for its durability, polyethylene can withstand various chemical conditions without degrading.
  • Due to its lightweight nature, it鈥檚 ideal for making products like film, plastic bags, and containers.
  • It exhibits excellent insulative properties, making it useful for packaging and electrical insulation.
The production of polyethylene exemplifies the power of polymerization, transforming simple ethylene monomers into a resilient and adaptable polymer.
Reactive Sites
Reactive sites on a monomer are specific locations where bonds can form, enabling the monomer to link with others:
  • These sites are typically characterized by the presence of double or triple bonds, such as those found in ethylene.
  • A monomer needs at least two reactive sites to effectively participate in polymerization, allowing the formation of long chains.
  • The nature and number of reactive sites on a monomer determines its ability to form complex polymers.
For instance, while ethylene has reactive sites due to its double bond, methane lacks them, making it unsuitable for polymerization. Reactive sites are the key driver in the formation and characteristics of polymers.

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Most popular questions from this chapter

Amorphous silica, \(\mathrm{SiO}_{2}\), has a density of about \(2.2 \mathrm{~g} / \mathrm{cm}^{3}\), whereas the density of crystalline quartz, another form of \(\mathrm{SiO}_{2}\), is \(2.65 \mathrm{~g} / \mathrm{cm}^{3}\). Which of the following statements is the best explanation for the difference in density? (a) Amorphous silica is a network-covalent solid, but quartz is metallic. (b) Amorphous silica crystallizes in a primitive cubic lattice. (c) Quartz is harder than amorphous silica. (d) Quartz must have a larger unit cell than amorphous silica. (e) The atoms in amorphous silica do not pack as efficiently in three dimensions as compared to the atoms in quartz.

(a) Draw a picture that represents a crystalline solid at the atomic level. (b) Now draw a picture that represents an amorphous solid at the atomic level.

(a) The density of diamond is \(3.5 \mathrm{~g} / \mathrm{cm}^{3}\), and that of graphite is \(2.3 \mathrm{~g} / \mathrm{cm}^{3}\). Based on the structure of buckminsterfullerene, what would you expect its density to be relative to these other forms of carbon? (b) X-ray diffraction studies of buckminsterfullerene show that it has a face-centered cubic lattice of \(\mathrm{C}_{60}\) molecules. The length of an edge of the unit cell is \(142 \mathrm{pm} .\) Calculate the density of buckminsterfullerene.

The electrical conductivity of aluminum is approximately \(10^{9}\) times greater than that of its neighbor in the periodic table, silicon. Aluminum has a face-centered cubic structure, and silicon has the diamond structure. A classmate of yours tells you that density is the reason aluminum is a metal but silicon is not; therefore, if you were to put silicon under high pressure, it too would act like a metal. Discuss this idea with your classmates, looking up data about Al and Si as needed.

Classity each of the following statements as true or false: (a) For molecular solids, the melting point generally increases as the strengths of the covalent bonds increase. (b) For molecular solids, the melting point generally increases as the strengths of the intermolecular forces increase.
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