The Chemistry of Materials

MYP Unit Framework

Key Concept: SYSTEMS Related Concepts: Properties, Patterns, Evidence Global Context: Scientific and Technical Innovation (How does understanding material structure enable technological advancement?) Statement of Inquiry: The properties of materials are determined by their structure at the atomic and molecular level.

Inquiry Questions

ATL Skills

• Thinking: Identify patterns in the periodic table; predict properties based on structure
• Research: Conduct lab investigations and interpret experimental evidence
• Communication: Write lab reports using scientific conventions; model molecular structures
• Self-Management: Work safely with chemicals and laboratory equipment

1. The Periodic Table — Patterns and Trends

History of the Periodic Table

Dmitri Mendeleev (1869) arranged elements by atomic mass, leaving gaps for undiscovered elements and predicting their properties. The modern table is arranged by atomic number (protons).

Key Patterns

• Groups (Vertical Columns): Elements in the same group have the same number of outer electrons and similar chemical properties.
• Periods (Horizontal Rows): Each period represents a new electron shell.

Trends Across a Period

• Atomic Radius: Decreases across a period — more protons pull electrons closer
• Electronegativity: Increases across a period — atoms attract electrons more strongly
• Ionisation Energy: Increases across a period — harder to remove an electron

Trends Down a Group

• Atomic Radius: Increases — more electron shells
• Electronegativity: Decreases — outer electrons further from nucleus
• Reactivity: Increases for metals; decreases for non-metals

Groups of Interest

• Group 1 (Alkali Metals): Highly reactive; one outer electron; react violently with water
• Group 7 (Halogens): Reactive non-metals; seven outer electrons; form salts with metals
• Group 0 (Noble Gases): Full outer shell; unreactive; used in lighting and welding

2. Chemical Bonding

Why Do Atoms Bond?

Atoms bond to achieve a full outer electron shell (octet rule), which is the most stable configuration.

Ionic Bonding

Mechanism: Transfer of electrons from metal to non-metal. The metal becomes a positive ion (cation); the non-metal becomes a negative ion (anion). Opposite charges attract.

Properties of Ionic Compounds:

• High melting and boiling points (strong electrostatic forces)
• Conduct electricity when molten or dissolved (ions are mobile)
• Usually soluble in water
• Form crystal lattices

Example: Sodium chloride (NaCl) — Na gives one electron to Cl.

Covalent Bonding

Mechanism: Sharing of electrons between non-metal atoms. Each shared pair constitutes one covalent bond.

Properties of Covalent Substances:

• Simple Molecular: Low melting/boiling points (weak intermolecular forces); do not conduct electricity (water, carbon dioxide)
• Giant Covalent: Very high melting points; hard; do not conduct (except graphite) — diamond, graphite, silicon dioxide

Metallic Bonding

Mechanism: Metal atoms release outer electrons into a 'sea of delocalised electrons.' Positive metal ions are held together by attraction to the electron sea.

Properties of Metals:

• Conduct heat and electricity (delocalised electrons)
• Malleable and ductile (layers of ions can slide)
• High melting points (strong metallic bonds)

3. Acids, Bases, and pH

Definitions

• Acid: Substance that donates H+ ions in solution
• Base: Substance that accepts H+ ions in solution
• Alkali: A base that dissolves in water
• pH Scale: 0-14 — measures hydrogen ion concentration

The pH Scale

Acid-Base Reactions (Neutralisation)

Acid + Base → Salt + Water

Example: HCl + NaOH → NaCl + H₂O

Uses of Neutralisation

• Antacids for indigestion (base neutralises excess stomach acid)
• Treating acidic soil with lime (calcium hydroxide)
• Treating industrial waste before disposal

4. Metals and Non-Metals

Physical Properties Comparison

Reactivity Series of Metals

Most reactive → Least reactive: K, Na, Ca, Mg, Al, Zn, Fe, Sn, Pb, H, Cu, Ag, Au

Displacement Reactions

A more reactive metal will displace a less reactive metal from its compound.

Example: Fe + CuSO₄ → FeSO₄ + Cu (iron displaces copper)

Extracting Metals

• Unreactive metals (Au, Ag) — found native
• Moderately reactive (Fe, Zn) — extracted by reduction with carbon or carbon monoxide
• Highly reactive (K, Na, Al) — extracted by electrolysis

5. The Chemistry of Everyday Materials

Polymers

Long-chain molecules made of repeating units (monomers). Natural (silk, wool, cellulose) and synthetic (plastic, nylon, polyester).

Properties depend on chain length, branching, and cross-linking.

Alloys

Mixtures of a metal with other elements. Alloys often have superior properties to pure metals.

• Steel: Iron + carbon (stronger than pure iron)
• Bronze: Copper + tin (harder than copper)
• Brass: Copper + zinc (corrosion resistant)

Composite Materials

Two or more materials combined to create properties superior to either alone.

• Fibreglass: Glass fibres in polymer resin (strong and light)
• Concrete: Cement + aggregate (strong in compression)
• Carbon fibre: Carbon fibres in epoxy (very strong, very light)

Summative Assessment

Task: Scientific report on a practical investigation (800-1000 words) OR research presentation on a material of choice.

Criteria:

• A: Knowing and Understanding — Explain chemical concepts accurately
• B: Inquiring and Designing — Design an investigation with clear variables
• C: Processing and Evaluating — Process data, evaluate methods, discuss uncertainty
• D: Reflecting on the Impacts of Science — Discuss real-world applications and implications

Option 1: Investigate the reactivity of different metals by observing their reactions with acid. Predict and explain the order of reactivity.

Option 2: Research the development of a specific material (e.g., Kevlar, graphene, biodegradable plastic). Explain how its properties relate to its structure and discuss its impact on society.

Option 3: Design an investigation to test the effectiveness of different antacids using titration or pH measurement.

Formative Assessment

• Periodic table quiz: group and period identification
• Drawing electron configurations and dot-cross diagrams
• Modeling molecules using ball-and-stick kits
• pH investigation: testing common household substances
• Displacement reaction mini-lab

Interdisciplinary Connections

• Design: Material selection for product design — why specific materials are chosen
• Environmental Science: Biodegradable materials, plastic pollution, recycling technologies
• Art: Pigments and dyes throughout history — chemistry of colour
• History: Bronze Age, Iron Age — how material discovery shaped civilisation

Service as Action

• Plastics Audit: Conduct a school plastics audit. Research alternatives and present recommendations for reducing single-use plastics.
• Chemistry Demonstration: Prepare and present safe chemistry demonstrations for younger students to spark interest in materials science.

IB Learner Profile

• Inquirers: Investigate the structure and properties of materials through experimentation
• Knowledgeable: Understand atomic structure, bonding, and the periodic table
• Thinkers: Apply chemical principles to explain the properties of materials
• Caring: Consider the environmental and social impacts of material production and disposal

Self-Test

1. What information does the periodic table provide about elements?
2. Describe TWO trends across a period in the periodic table.
3. What is the difference between ionic and covalent bonding?
4. Explain why ionic compounds conduct electricity when molten but not when solid.
5. What is the pH range of a strong acid? A strong alkali?
6. Write the word equation for neutralisation.
7. What is the reactivity series? Use it to predict whether iron can displace copper from copper sulfate.
8. Why are alloys often stronger than pure metals?
9. Name TWO types of composite materials and explain their advantages.
10. Why is graphene considered a revolutionary material?

This unit aligns with IB MYP Sciences guide, developed for Year 4 (Class 9) students.