Properties of MetalsCambridge IGCSE Chemistry: Revision notes
Section 1
What are the key physical properties that define metals?
Metals possess a distinct set of physical properties that make them useful materials. The main physical properties include:
- Thermal conductivity: Metals conduct heat very well; they allow heat energy to pass through them quickly
- Electrical conductivity: Metals conduct electricity very well; they allow electric current to flow through them easily
- Malleability: Metals can be hammered or rolled into thin sheets without breaking
- Ductility: Metals can be stretched into wires without breaking
- Melting and boiling points: Most metals have high melting and boiling points (though there are exceptions like mercury)
- Appearance: Metals are generally shiny and lustrous
- Density: Most metals are dense solids at room temperature
These properties arise from the delocalised electrons in the metallic structure, which move freely throughout the material.
When comparing metals and non-metals, examiners expect you to name both properties and explain why metals have them better. For example: 'Copper is a better thermal conductor than sulphur because copper has delocalised electrons that can transfer kinetic energy quickly.'
Section 2
How do the physical properties of metals compare with non-metals?
| Property | Metals | Non-metals |
|---|---|---|
| Thermal conductivity | Good thermal conductors | Poor thermal conductors (insulators) |
| Electrical conductivity | Good electrical conductors | Poor electrical conductors (insulators) |
| Malleability | Malleable — can be shaped by hammering | Brittle — shatter when hammered |
| Ductility | Ductile — can be drawn into wires | Brittle — cannot be stretched into wires |
| Melting and boiling points | Mostly high (except mercury) | Mostly low (with some exceptions) |
| Appearance | Shiny and lustrous | Dull; may be transparent or opaque |
| Density | Generally high density | Generally lower density |
Key comparison principle: Metals conduct heat and electricity well because they have delocalised electrons that move freely. Non-metals lack delocalised electrons, so they are insulators. Metals are malleable and ductile because their atoms can slide past each other without breaking the metallic bonding; non-metals are brittle because covalent bonds break easily under stress.
Students often say metals are 'better' than non-metals, but examiners want comparative language: 'Metals conduct electricity better than non-metals' or 'Non-metals are insulators whereas metals are conductors.' Use 'whereas' or 'compared to' for clearer comparison.
Think of metallic bonding like a crowd of people (positive ions) in a mosh pit with security guards (delocalised electrons) constantly moving through them. The guards can deliver messages (electricity/heat) quickly. In non-metals, the atoms are glued in fixed positions, so nothing can move through easily.
Section 3
What happens when metals react with dilute acids?
Metals react with dilute acids to produce hydrogen gas and a metal salt. This is one of the most important reactions to know for the exam.
General equation: Metal + Dilute acid → Metal salt + Hydrogen gas
Specific examples:
-
Magnesium + dilute hydrochloric acid:
- Mg + 2HCl → MgCl₂ + H₂↑
- Reaction is vigorous; hydrogen burns with a pop sound
-
Iron + dilute sulphuric acid:
- Fe + H₂SO₄ → FeSO₄ + H₂↑
- Reaction is moderate; steady fizzing
-
Zinc + dilute hydrochloric acid:
- Zn + 2HCl → ZnCl₂ + H₂↑
- Reaction is moderate; steady fizzing
Order of reactivity with dilute acids (most to least reactive): Magnesium > Zinc > Iron > Copper (copper does not react with dilute acids)
Observable signs of reaction:
- Vigorous or steady fizzing (hydrogen gas evolved)
- Solution becomes warm
- Solid metal slowly disappears
- Solution changes colour (due to metal salt formation)
Examiners test whether you can predict products and write balanced equations. If asked about a metal reacting with dilute acid, always predict hydrogen gas as one product and a metal salt as the other. Check that the equation is balanced.
Predict the products when zinc reacts with dilute hydrochloric acid and write a balanced equation. Answer: Zinc + dilute hydrochloric acid → zinc chloride + hydrogen gas. Balanced equation: Zn + 2HCl → ZnCl₂ + H₂↑. The hydrogen can be tested with a 'pop' sound using a lighted splint.
Section 4
How do metals react with oxygen?
Metals react with oxygen (especially when heated) to form metal oxides. This is a combustion reaction.
General equation: Metal + Oxygen → Metal oxide
Specific examples:
-
Magnesium burns in oxygen (bright white flame):
- 2Mg + O₂ → 2MgO
- Very vigorous; produces intense white light
-
Iron burns in oxygen (sparks, dark red product):
- 3Fe + 2O₂ → Fe₃O₄ (or 4Fe + 3O₂ → 2Fe₂O₃)
- Vigorous; produces sparks and dark red/black solid
-
Copper heats in oxygen (black product):
- 2Cu + O₂ → 2CuO
- Moderate; turns black when heated
-
Sodium burns in oxygen (yellow flame):
- 4Na + O₂ → 2Na₂O₂
- Very vigorous; pale yellow sodium peroxide forms
Order of reactivity with oxygen (most to least reactive): Sodium > Magnesium > Iron > Copper
Observable signs of reaction:
- Vigorous burning or glowing
- Coloured flames (sodium = yellow, magnesium = white)
- Metal becomes a solid product (the oxide)
- Heat and light released
When writing equations for metals burning in oxygen, balance oxygen atoms carefully — it often appears as O₂ on the left. Check your equation twice: do the numbers of each element match on both sides?
Students often forget that magnesium oxide is MgO (not MgO₂) and that iron forms Fe₃O₄ or Fe₂O₃, not FeO. Memorise the correct formulas for common metal oxides.
Section 5
How do metals react with water and steam?
Metals react with water (cold water or steam) to produce metal hydroxides or oxides and hydrogen gas. The vigour of reaction depends on the metal's position in the reactivity series.
Reactions with cold water:
-
Sodium reacts vigorously with cold water:
- 2Na + 2H₂O → 2NaOH + H₂↑
- Vigorous; sodium skitters on water surface; hydrogen may ignite
-
Calcium reacts moderately with cold water:
- Ca + 2H₂O → Ca(OH)₂ + H₂↑
- Moderate; steady bubbling
-
Magnesium reacts very slowly with cold water:
- Mg + 2H₂O → Mg(OH)₂ + H₂↑
- Very slow at room temperature; no visible reaction
Reactions with steam (heated water):
-
Magnesium reacts vigorously with steam:
- Mg + H₂O(g) → MgO + H₂↑
- Vigorous; produces white powder (magnesium oxide) and hydrogen gas
-
Iron reacts vigorously with steam:
- 3Fe + 4H₂O(g) → Fe₃O₄ + 4H₂↑
- Vigorous; red-hot iron becomes grey-black; hydrogen evolved
Order of reactivity with water (most to least reactive): Sodium > Calcium > Magnesium (slowly with cold water, vigorously with steam) > No reaction with zinc, iron, copper
Observable signs:
- Vigorous or slow fizzing (hydrogen evolved)
- Solution becomes warm or hot
- Solid products form (hydroxides or oxides)
Examiners distinguish between cold water and steam reactions. Know that magnesium barely reacts with cold water but reacts vigorously with steam. Write clear equations showing either H₂O (liquid) or H₂O(g) (steam) to demonstrate this understanding.
A student heats magnesium ribbon in steam. Predict the products and write a balanced equation. Answer: Magnesium reacts with steam (not liquid water at room temperature) to produce magnesium oxide and hydrogen gas. Equation: Mg + H₂O(g) → MgO + H₂↑. A white powder (MgO) forms and hydrogen gas is released.
Must Know
- Metals conduct heat and electricity well because they contain delocalised electrons that move freely; non-metals are insulators because their electrons are fixed in place
- Metals are malleable and ductile (can be shaped and stretched) because their atoms slide past each other under stress whilst maintaining metallic bonding; non-metals are brittle and shatter
- Metals react with dilute acids to produce a metal salt and hydrogen gas (e.g. Mg + 2HCl → MgCl₂ + H₂↑); reactivity order is Mg > Zn > Fe > Cu
- Metals burn in oxygen to form metal oxides with heat and light (e.g. 2Mg + O₂ → 2MgO); sodium and magnesium burn most vigorously
- Metals react with water/steam to produce hydroxides or oxides and hydrogen gas; sodium reacts vigorously with cold water, magnesium reacts very slowly with cold water but vigorously with steam
- Always balance equations carefully and identify products correctly: metal + acid → salt + H₂; metal + O₂ → oxide; metal + H₂O → hydroxide/oxide + H₂
That's the notes covered.
Carry on to the next subtopic.