Structure 2.4 From Models to Materials - Notes Overview

Structure 2.4 From Models to Materials

Activity: Bond Behavior

• Predict locations of hydrogen-oxygen bonds in the bonding triangle.

• Calculate AX and X values to compare predictions with actual findings.

Practice Questions: Electronegativity and Bond Properties

• Mean Electronegativity and Bond Differences:

  • Analyze how different electronegativity values affect the properties of compounds.

  • Discuss expected properties based on bond type (ionic, covalent).

Linking Question: Properties of Composites

• Unique Properties of Composites (e.g., reinforced concrete):

  • Combinations of ionic, covalent, and metallic bonding result in enhanced mechanical properties.

Alloys (Structure 2.4.3)

• Definition and Characteristics of Alloys:

  • Mixtures of metallic and non-metallic elements.

  • Retain metallic properties like electrical conductivity and lustre.

  • Exhibit enhanced properties (e.g., hardness, corrosion resistance).

Properties of Alloys

• Structure: Different cation sizes disrupt the metallic lattice, enhancing strength.

• Comparison to Pure Metals: Pure metals have uniform cation sizes, allowing easy sliding under force, leading to malleability.

• Reinforcement: Adding atoms of different radii enhances strength by resisting layer movement during stress.

Examples of Alloys

• NaK Alloy: A sodium-potassium alloy with a lower melting point, used as a nuclear reactor coolant.

• Memory Metals: Alloys that return to their original shape when heated, used in applications prone to deformation.

• Steel: Iron combined with carbon, creating stronger, harder materials for various industries.

Rusting and Degradation of Steel

• Rusting transforms iron into hydrated iron(III) oxide (an ionic compound).

• Economic implications as it affects ships, bridges needing protection from corrosion.

• Protection methods: barrier (painting) and sacrificial (galvanizing).

• Stainless Steel: Iron with chromium; the oxide layer prevents rusting, making it suitable for medical and kitchen applications.

Carbon Content in Steel

• Medium steel (0.3%-0.6% carbon) hardness can be assessed through Vickers hardness tests; graph analysis required to relate carbon content and hardness.

Other Alloys

• Bronze: Copper and tin, used historically in shipbuilding, known for corrosion resistance.

• Brass: Copper and zinc, highly malleable and used for acoustic properties in music instruments.

Polymers (Structure 2.4.4)

• Definition and Characteristics: Covalently bonded materials, low thermal/electrical conductivity, low density.

• Monomers and Polymerization: Long chains formed by joining smaller molecules (monomers) via addition or condensation reactions.

Repeating Units

• Importance of Repeating Units: Describe polymer structure through the repeating unit; indicates polymer length.

• Types of Polymers: Natural (cellulose, DNA) vs. synthetic (nylon, plastics).

Properties of Polymers

• Strong due to macromolecular nature; low electrical conductivity due to lack of moving charged particles.

• High thermal melting and boiling points linked to many intermolecular forces across polymer chains.

Environmental Impact of Plastics

• Challenges with Recycling: Environments such as landfills and oceans affected by non-biodegradable plastic waste. Most plastics often incinerated instead of recycled.

• Biodegradable Plastics: Designed to decompose with microbial action; involves considerations regarding the agricultural impacts of raw material sourcing.

Global Impact of Science

• Green Chemistry Principles: Advocate for renewable materials and biodegradable plastics, addressing the ecological footprint of traditional plastics.

• Microplastics Issues: Long-term effects on health and the environment with microplastics detected in blood.

Addition Polymers (Structure 2.4.5)

• Polymerization Process: Involves monomers with double bonds forming a polymer through breaking these bonds. Example: Polyethene from ethene monomers.

• Comparison of Monomer and Polymer Properties: Different structural characteristics lead to different physical properties.

Practice Questions on Addition Polymers

• Analyze and deduce structures of monomers and polymers from given sections, highlight the differences in physical and chemical properties between them.

Linking Questions

• Discuss why specific functional groups enable addition reactions and clarify why atom economy is uniformly 100% for addition polymerization reactions when applied in practice.