Question

The molecular formula of \(n\) -decane is \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{8} \mathrm{CH}_{3} .\) Decane is not considered a polymer, whereas polyethylene is. What is the distinction?

Short answer

The distinction between n-decane and polyethylene lies in their molecular structures and whether they are comprised of repeating monomeric units. n-Decane is a simple hydrocarbon with a linear chain of 10 carbon and 22 hydrogen atoms, and does not consist of any repeating monomeric units. Polyethylene is a large molecule formed by the addition polymerization of ethylene monomers, resulting in a long chain of repeating ethylene units. Therefore, n-decane is not considered a polymer, whereas polyethylene is.

Step-by-step solution

Understanding the molecular structure of n-decane

n-Decane is an alkane hydrocarbon with the molecular formula \(\mathrm{CH}_{3}(\mathrm{CH}_{2})_{8}\mathrm{CH}_{3}\). It consists of a linear chain of 10 carbon atoms (\(C\)) and 22 hydrogen atoms (\(H\)). The molecular structure is as follows: H H H H H H H H H H | | | | | | | | | | C-C-C-C-C-C-C-C-C-C | | | | | | | | | | H H H H H H H H H H

Understanding the molecular structure of polyethylene

Polyethylene is a polymer with repeating ethylene units. Ethylene has the molecular formula \(\mathrm{C}_{2}\mathrm{H}_{4}\) and its structure is as follows: H H | | C=C | | H H In polyethylene, the double bond between the carbon atoms in ethylene is broken, and the ethylene units link together to form a long chain. The molecular structure of polyethylene is represented as \((\mathrm{C}_{2}\mathrm{H}_{4})_{n}\), where n is the number of repeating units.

Understanding the concept of polymers

Polymers are large molecules formed by the combination of smaller, repeating units called monomers. The process by which monomers link together to form a polymer is called polymerization. There are two main types of polymerization: addition (chain-growth) polymerization and condensation (step-growth) polymerization. Polyethylene, for example, is formed by the addition polymerization of ethylene monomers. The double bond between the carbon atoms in the ethylene monomer is broken, and the ethylene units join together in a long chain, creating a polymer.

Explaining the distinction between n-decane and polyethylene

The distinction between n-decane and polyethylene lies in their molecular structures and whether they are comprised of repeating monomeric units. n-Decane is a simple hydrocarbon formed of a linear chain of 10 carbon and 22 hydrogen atoms and does not consist of any repeating monomeric units. Polyethylene, on the other hand, is a large molecule formed by the addition polymerization of ethylene monomers, resulting in a long chain of repeating ethylene units. As a result, n-decane is not considered a polymer, whereas polyethylene is, because only polyethylene is made up of repeating monomeric units joined together through a polymerization process.

Key concepts

n-Decane

n-Decane is an alkane hydrocarbon recognized for its straightforward linear molecular structure. Its molecular formula is \(\mathrm{CH}_{3}(\mathrm{CH}_{2})_{8}\mathrm{CH}_{3}\), which consists of ten carbon (C) atoms and twenty-two hydrogen (H) atoms. This molecule forms a straight chain, much like a string of pearls connected in a line. It's a significant component in gasoline and often used in various industrial applications. However, unlike polymers, it does not consist of repeating units, which is why n-decane is not categorized as a polymer.

Features of n-decane include:

• Simple structure: linear chain of carbon atoms
• Each carbon atom is singly bonded, resulting in no branching
• Relatively low molecular weight compared to polymers

Understanding its structure helps in distinguishing it from complex polymers.

Polyethylene

Polyethylene is one of the most common polymers, found in various plastic products like bottles, bags, and toys. The fundamental building block of polyethylene is ethylene, a hydrocarbon with the molecular formula \(\mathrm{C}_{2}\mathrm{H}_{4}\). In its polymer form, the ethylene monomers undergo a process where their double bonds open and link together, forming a long chain.

Key characteristics of polyethylene include:

• Composed of repeating units of ethylene
• Flexible and durable material
• Can vary in density, affecting its toughness and application

The process by which ethylene becomes polyethylene is a classical example of how repeating units form elaborate polymers through polymerization.

Molecular Structure

The molecular structure of a compound defines its physical and chemical properties. For hydrocarbons like n-decane, the structure is a straight chain of carbon atoms each bound to hydrogen atoms. The structure can be represented visually, vividly showing the connections between atoms.

In contrast, the structure of polymers like polyethylene varies as they include long chains of repeating units. This repeating pattern significantly alters the properties of the substance, resulting in changes like increased stability and flexibility.

Highlights of molecular structures include:

• Linear structure in n-decane
• Repetitive pattern in polyethylene
• Impact on material properties

This aspect is central to understanding the nature of compounds and how these structures influence their functions in practical applications.

Polymerization

Polymerization is a chemical process through which monomers join to form a polymer. There are two main types:

• Addition polymerization: involves monomers adding to each other without the loss of any atom. Polyethylene is created this way, where ethylene monomers connect to form long chains.
• Condensation polymerization: involves the combination of monomers, with the elimination of small molecules like water or alcohol.

This process is what sets polymers apart from non-polymers. By linking monomers to form extensive networks, polymerization transforms simple substances into versatile, durable materials like plastics.

Monomers

Monomers are small molecules that serve as the building blocks for polymers. Each monomer joins with others to form the extensive chains or networks characteristic of polymers. In the case of polyethylene, the monomer is ethylene, which through polymerization, forms long chains that give polyethylene its plastic properties.

Important aspects of monomers include:

• Building blocks of polymers
• Diverse in nature, resulting in different kinds of polymers
• Influence the properties of the resulting polymer

Understanding monomers is crucial because they determine the polymer type and ultimately its applications in the real world. They are the starting point for a material that can be adapted for countless uses.