Ch.12 - Solids and Modern Materials

Brown - Chemistry: The Central Science 14th Edition

Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook

Brown 14th Edition

Ch.12 - Solids and Modern Materials

Problem 9b

Chapter 12, Problem 9b

Shown here are cartoons of two different polymers. Which one would have the higher melting point?

Verified step by step guidance

Identify the two types of polymer structures shown in the image: Polymer I has linear chains, and Polymer II has branched chains.

Recall that the melting point of a polymer is influenced by the strength of intermolecular forces and the degree of packing of the polymer chains.

Understand that linear polymers (Polymer I) can pack more closely together, leading to stronger intermolecular forces (e.g., van der Waals forces) and higher crystallinity.

Recognize that branched polymers (Polymer II) have irregular structures that prevent close packing, resulting in weaker intermolecular forces and lower crystallinity.

Conclude that Polymer I, with its linear chains, would have a higher melting point compared to Polymer II, which has branched chains.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Video duration:

Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Polymer Structure

Polymers are large molecules made up of repeating structural units called monomers. The arrangement of these monomers can significantly affect the properties of the polymer, including its melting point. Linear polymers, like those depicted in the left image, have a more organized structure, allowing for stronger intermolecular forces compared to branched polymers, which are more irregular and can lead to weaker interactions.

Intermolecular Forces

The melting point of a substance is largely determined by the strength of the intermolecular forces acting between its molecules. In polymers, stronger intermolecular forces, such as hydrogen bonding or van der Waals forces, result in higher melting points. Linear polymers typically exhibit stronger intermolecular forces due to their ability to pack closely together, while branched polymers have more space between chains, reducing these forces.

Crystallinity

Crystallinity refers to the degree to which a polymer's molecular chains are ordered. Higher crystallinity usually leads to higher melting points because the ordered structure allows for stronger intermolecular interactions. Linear polymers tend to be more crystalline than branched ones, which are often amorphous, resulting in lower melting points due to less efficient packing and weaker interactions.

Recommended video:

Guided course

01:31

Crystalline Solids Structure

Related Practice

Textbook Question

Silicon is the fundamental component of integrated circuits. Si has the same structure as diamond. (a) Is Si a molecular, metallic, ionic, or covalent-network solid?

Textbook Question

The accompanying image shows photoluminescence from four different samples of CdTe nanocrystals, each embedded in a polymer matrix. The photoluminescence occurs because the samples are being irradiated by a UV light source. The nanocrystals in each vial have different average sizes. The sizes are 4.0, 3.5, 3.2, and 2.8 nm. (a) Which vial contains the 4.0-nm nanocrystals?

Textbook Question

Which of these molecular fragments would you expect to be more likely to give rise to electrical conductivity? Explain your reasoning. (a)

(b)

Textbook Question

The electronic structure of a doped semiconductor is shown here. (c) Which region of the diagram represents the band gap?

Textbook Question

Which arrangement of cations (yellow) and anions (blue) in a lattice is the more stable? Explain your reasoning. (a)

(b)