9.1 Properties of Metals: Revision Notes
1. Overview
Metals occupy the left and center of the Periodic Table and account for about 80% of all elements. Understanding their physical and chemical properties is essential for determining their uses in construction, electronics, and industry, as well as predicting how they react with the environment.
Key Definitions
- Malleable: Capable of being hammered or pressed into thin sheets without breaking.
- Ductile: Capable of being drawn out into thin wires.
- Thermal Conductor: A material that allows heat to pass through it easily.
- Electrical Conductor: A material that allows an electric current to flow through it.
- Lustrous: Having a shiny or reflective surface (when freshly cut or polished).
- Sonorous: Making a deep, ringing sound when struck.
Core Content
A. Physical Properties: Metals vs. Non-Metals
Metals and non-metals show distinct physical differences based on their atomic structures.
| Property | Metals | Non-Metals |
|---|---|---|
| Thermal Conductivity | Good conductors | Poor conductors (insulators) |
| Electrical Conductivity | Good conductors (due to mobile electrons) | Poor conductors (except graphite) |
| Malleability/Ductility | Malleable and ductile | Brittle (shatter when struck) |
| Melting/Boiling Points | Generally high | Generally low |
| Appearance | Shiny (lustrous) | Dull |
| Density | Usually high density | Usually low density |
B. Chemical Properties of Metals
Metals tend to lose electrons to form positive ions (cations). Their reactivity varies depending on their position in the reactivity series.
1. Reaction with Dilute Acids Most metals react with dilute acids to produce a salt and hydrogen gas.
- Word Equation: Metal + Acid → Salt + Hydrogen gas
- Symbol Equation: $Mg(s) + 2HCl(aq) \rightarrow MgCl_2(aq) + H_2(g)$
2. Reaction with Cold Water Very reactive metals (like Group I) react with cold water to form a metal hydroxide and hydrogen gas.
- Word Equation: Metal + Water → Metal Hydroxide + Hydrogen gas
- Symbol Equation: $2Na(s) + 2H_2O(l) \rightarrow 2NaOH(aq) + H_2(g)$
3. Reaction with Steam Less reactive metals (like Magnesium or Zinc) do not react easily with cold water but will react with steam to form a metal oxide and hydrogen gas.
- Word Equation: Metal + Steam → Metal Oxide + Hydrogen gas
- Symbol Equation: $Mg(s) + H_2O(g) \rightarrow MgO(s) + H_2(g)$
4. Reaction with Oxygen Metals react with oxygen to form metal oxides. This is often an oxidation reaction.
- Word Equation: Metal + Oxygen → Metal Oxide
- Symbol Equation: $4Li(s) + O_2(g) \rightarrow 2Li_2O(s)$
- Symbol Equation: $2Mg(s) + O_2(g) \rightarrow 2MgO(s)$
Extended Content (Extended Only)
There is no specific extended curriculum content for this sub-topic (9.1) beyond the core requirements.
Key Equations
| Reaction Type | General Equation | Example with State Symbols |
|---|---|---|
| Metal + Acid | $M + HX \rightarrow Salt + H_2$ | $Zn(s) + H_2SO_4(aq) \rightarrow ZnSO_4(aq) + H_2(g)$ |
| Metal + Water | $M + H_2O \rightarrow M(OH)_n + H_2$ | $Ca(s) + 2H_2O(l) \rightarrow Ca(OH)_2(aq) + H_2(g)$ |
| Metal + Steam | $M + H_2O \rightarrow MO + H_2$ | $Zn(s) + H_2O(g) \rightarrow ZnO(s) + H_2(g)$ |
| Metal + Oxygen | $M + O_2 \rightarrow MO$ | $2Cu(s) + O_2(g) \rightarrow 2CuO(s)$ |
- Symbols: $s$ = solid, $l$ = liquid, $g$ = gas, $aq$ = aqueous (dissolved in water).
Common Mistakes to Avoid
- ❌ Wrong: Stating that metals react with water to form oxides.
- ✓ Right: Metals react with cold water to form hydroxides, but react with steam to form oxides.
- ❌ Wrong: Writing hydrogen as $H$ in equations.
- ✓ Right: Hydrogen is a diatomic molecule; always write it as $H_2(g)$.
- ❌ Wrong: Forgetting state symbols when requested.
- ✓ Right: Always include $(s), (l), (g),$ or $(aq)$ to describe the physical state of each substance.
Exam Tips
- Command Words:
- "State": Give a brief fact (e.g., "State two physical properties of metals" → High melting point and good electrical conductivity).
- "Explain": You must give a reason. If asked why metals conduct electricity, mention "delocalized electrons that are free to move."
- "Name": Give the specific chemical name (e.g., "Name the gas produced" → Hydrogen).
- Question Types: Expect questions where you are given an "unknown element X" and its properties (e.g., it is brittle and a poor conductor). You will be asked to identify it as a non-metal.
- Real-world Contexts: Exams often ask why Copper is used for wiring (ductility and electrical conductivity) or why Aluminum is used for pans (thermal conductivity).
- Key Identification: If a question mentions a "gas that pops with a lighted splint," it is identifying Hydrogen ($H_2$) produced from a metal reacting with acid or water.