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 nature: n-decane is a small molecule with a finite number of atoms and a defined molecular formula (\(CH_3(CH_2)_8CH_3\)), while polyethylene is a macromolecule consisting of a large number of repeating ethylene units (\(-CH_2-CH_2-\)_n) with varying chain length.

Step-by-step solution

Define n-decane

n-decane is an alkane hydrocarbon with the molecular formula: \(CH_3(CH_2)_8CH_3\). It has a chain of 10 carbon atoms (hence the 'dec' in its name), each one of them bonded to hydrogen atoms through single bonds.

Define polyethylene

Polyethylene is a polymer made from ethylene monomers (\(C_2H_4\)). It is a long chain hydrocarbon, where each carbon atom is connected to two hydrogen atoms and the backbone of the chain consists of carbon-carbon single bonds. The formula for polyethylene can be represented as (\(-CH_2-CH_2-\)_n) where n represents the number of repeating units.

Compare n-decane and polyethylene

n-decane is a single molecule, while polyethylene is a polymer made up of many ethylene monomers connected together. The key distinction between them lies in their nature: n-decane is a small molecule with a finite number of atoms and a defined molecular formula, while polyethylene is a macromolecule, consisting of a large number of repeating units (\(n\)) that can vary greatly in size.

Conclusion

In conclusion, the distinction between n-decane and polyethylene lies in the fact that n-decane is a single, well-defined molecule, whereas polyethylene is a polymer comprising many repeating ethylene units, forming a large macromolecule with varying chain length.

Key concepts

Understanding n-Decane Structure

When considering the structure of n-decane, it's important to visualize it as a straight-chain alkane hydrocarbon with 10 carbon atoms connected linearly. The 'n' in n-decane stands for 'normal', which indicates that the carbon atoms are arranged in a continuous, unbranched chain. Its molecular formula is expressed as ewline \(CH_3(CH_2)_8CH_3\). Each carbon atom in this linear structure is single-bonded to other carbon atoms and to hydrogen atoms, following the general formula for alkanes, \(C_nH_{2n+2}\).

Understanding the structural simplicity of n-decane serves as a basis for contrasting it with complex polymers like polyethylene. In a hypothetical educational environment, I would suggest using molecular models to help students visualize and comprehend the linear structure of alkanes such as n-decane, which aids in grasping the foundational principles of organic chemistry.

Diving into Polyethylene Properties

Polyethylene is one of the most common polymers and is used in a wide array of everyday products due to its unique set of properties. It is known for being strong yet lightweight, which makes it ideal for plastic bags, bottles, and other containers. Polyethylene is chemically resistant, meaning it doesn't react with a lot of chemicals, and it's also an excellent insulator, preventing the passage of electricity and heat. Its physical properties like ductility and impact resistance make it useful in safety equipment and parts of vehicles.

From a structural viewpoint, polyethylene consists of long chains of –\(-CH_2-CH_2-\)_n– repeating units, where 'n' signifies the degree of polymerization and dictates the length of the polymer chain. This can greatly affect the physical properties of the material: low-density polyethylene (LDPE) has a more branched structure leading to less packing and lower strength, while high-density polyethylene (HDPE) has a more linear structure with minimal branching, resulting in tighter packing and greater strength. Educators might consider using demonstrations with everyday polyethylene objects to highlight its properties and encourage tactile learning.

Exploring the World of Macromolecules

Macromolecules are large, complex molecules that are essential to various biological and synthetic processes. They are typically composed of thousands, or even millions, of atoms linked in long chains. There are several types of macromolecules such as proteins, nucleic acids, carbohydrates, and synthetic polymers like polyethylene.

In the context of polymer chemistry, understanding macromolecules is crucial since they form the basis of materials science and various industrial applications. The chain-like structure of these macromolecules is responsible for their unique chemical and physical properties - from the elasticity of rubber to the toughness of kevlar. To enhance comprehension for students, it could be helpful to compare macromolecules with small-molecule counterparts and demonstrate the impact of chain length and composition on the overall properties of the substance.

Alkane Hydrocarbons Explained

Alkane hydrocarbons are organic compounds consisting entirely of hydrogen and carbon atoms, bound together by single covalent bonds. They are categorized as saturated hydrocarbons because they have the maximum number of hydrogen atoms possible on their carbon chain, without any double or triple bonds. These characteristics make alkanes relatively non-reactive compared with their unsaturated counterparts.

Alkanes can be found in chain-like structures, as seen in n-decane or branching isomers, and their general formula is represented as \(C_nH_{2n+2}\). In teaching, quantifying the number of possible isomers for a given number of carbon atoms can be an engaging way to explore organic chemistry concepts. For instance, the introduction of structural isomers illustrates molecular geometry and the influence of structure on physical and chemical properties.