IGCSE Chemistry Study Guide: Metals

Overview

This guide summarizes core concepts of metals, covering chemical properties, reactivity, extraction methods, and uses. Mastery requires understanding periodic trends and redox principles.

Syllabus Coverage: Core/Extended - Review specific section requirements for detailed study.

1. Properties and Structure

Physical Properties (Core)

  • Appearance: Typically solid at room temperature (exceptions: Mercury). Often shiny/lustrous.
  • State: Solid, malleable, ductile (can be hammered into sheets and drawn into wires).
  • Conductivity: Highly conductive of heat and electricity due to delocalized electrons in metallic bonding.
  • Density: Generally high density compared to non-metals.

Chemical Properties (Core/Extended)

  • Formation: Metals tend to lose electrons to achieve a stable electron configuration, forming positive ions (cations).
    • Reaction: $\text{Metal} \rightarrow \text{Metal}^+ + e^-$
  • Reactivity Series: Metals are arranged in the reactivity series based on their ease of oxidation potential. Higher up means higher reactivity.

2. Reactivity and Reactions

Reactions with Oxygen and Water (Core)

  • With Oxygen: Metals react vigorously forming metal oxides ($\text{M} + \text{O}2 \rightarrow \text{M}{\text{x}}\text{O}_{\text{y}}$). Reactivity determines oxide strength.
  • With Water: Highly reactive metals (Sodium, Potassium) react violently with water, producing a metal hydroxide and hydrogen gas.
    • Example: $\text{2Na}(\text{s}) + \text{2H}_2\text{O}(\text{g}) \rightarrow \text{2NaOH}(\text{aq}) + \text{H}_2(\text{g})$

Reactions in Acid Solutions (Core)

  • Reactive metals displace hydrogen from dilute acids, producing salt and hydrogen gas.
    • General equation: $\text{Metal} + 2\text{HCl} \rightarrow \text{MetalCl}_2 + \text{H}_2$
    • Caution: Metals less reactive than hydrogen (e.g., Gold) do not react with dilute acids.

Displacement Reactions and the Reactivity Series (Extended)

  • A more reactive metal can displace a less reactive metal from its salt solution.
    • Example: $\text{Zn}(\text{s}) + \text{CuSO}_4(\text{aq}) \rightarrow \text{ZnSO}_4(\text{aq}) + \text{Cu}(\text{s})$
  • The reactivity series acts as a predictor for potential displacement reactions.

3. Extraction of Metals (Extended)

A. Reduction Methods

Extraction generally requires converting metal compounds into pure element form. This involves a redox reaction. The ore must be reduced of oxygen.

  1. Low Reactivity/Easily Separated:

    • Often use electro-refining or electrolysis.
    • Example: Extraction of Copper (Cu). Electrolysis uses electrical energy to drive the reduction at two electrodes. $\text{Cu}^{2+} \rightarrow \text{Cu} + 2e^-$

  2. Medium Reactivity/Roasting:

    • Ore reacts with excess oxygen, forming a metal oxide ($\text{M}{\text{x}}\text{O}{\text{y}}$). This is easier than direct reaction. Oxygen gas supplies sufficient energy for initial reduction.
    • Example: Sulfide ore ($\text{ZnS}$) $\rightarrow$ Oxide ($\text{ZnO}$). Then, the oxide is reduced by carbon (carbon acts as a reducing agent): $\text{ZnO} + \text{C} \rightarrow \text{Zn} + \text{CO}$.

  3. High Reactivity/Smelting:

    • Ore requires strong reducing agents or high heat. A primary example is the extraction of Iron from haematite ($\text{Fe}_2\text{O}_3$) using a blast furnace, where coke ($\text{C}$) acts as both fuel and reducing agent.
    • Key reaction: $3\text{Fe}_2\text{O}_3 + \text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2$.

Comparison Table

Metal Example Ore Type Extraction Method Reducing Agent/Energy Source Key Concept
Copper ($\text{Cu}$) Sulfide ($\text{Cu}_2\text{S}$) Electrolysis / Roasting Electricity / Carbon Electro-refining, Displacement
Zinc ($\text{Zn}$) Carbonate ($\text{ZnCO}_3$) Roast/Smelt Carbon (C) Reducing agent required; $\text{ZnO}$ formation.
Iron ($\text{Fe}$) Oxide ($\text{Fe}_2\text{O}_3$) Blast Furnace / Smelting Coke ($\text{C}$) / Heat High temperature, carbon reduction process.
Aluminum ($\text{Al}$) Hydroxide/Mixed Oxides Electrolysis (Hall-Héroult) Electricity Very high energy input requires electrolysis.

4. Applications and Corrosion Prevention (Core)

Metal Corrosion Types

  • Oxidation: Loss of electrons, chemical reaction with oxygen (e.g., rusting).
    • Rusting (Iron): Requires both oxygen and water ($\text{Fe} + \text{O}_2 + \text{H}_2\text{O}$). Formula must balance the full process.
  • Galvanization: Coating iron/steel with a layer of zinc. Prevents oxidation by providing sacrificial protection.
  • Electroplating: Coating one metal surface with another (e.g., chrome plating). Used for appearance, corrosion resistance, or conductivity.

Prevention Methods

  1. Painting/Oil: Barrier protection; prevents contact with air and water.
  2. Galvanization: Sacrificial anode method using zinc ($\text{Zn}$). Zinc corrodes preferentially to iron.
  3. Alloying: Mixing metals (e.g., Stainless steel = Iron + Chromium). Alloying improves corrosion resistance by stabilizing the metal structure or forming protective oxide layers ($\text{Cr}_2\text{O}_3$).

5. Key Vocabulary Checklist

  • Malleable, Ductile, Luster
  • Delocalized Electrons (Metallic Bonding)
  • Oxidation/Reduction / Redox
  • Redox Half-Equation
  • Reactivity Series
  • Smelting / Roasting / Electrolysis
  • Galvanization / Electroplating