Metals and Non-Metals

Metals and non-metals show different physical properties and different electron behaviour. Across a period, the elements generally change from metallic to non-metallic character as the number of outer electrons increases.

1. Definition

A. Metal

A metal is an element that typically forms positive ions (cations) and has properties like good electrical conductivity and malleability.

B. Non-metal

A non-metal is usually a poor electrical conductor. In reactions, many non-metals gain electrons to form anions or share electrons in covalent bonds. Noble gases are non-metals with full outer shells and are very unreactive.

2. Key Ideas

• Metals tend to lose electrons to form cations (e.g. Na⁺, Mg²⁺).
• Non-metals tend to gain electrons to form anions (e.g. Cl⁻, O²⁻) or share electrons in covalent substances. These can be separate molecules or giant networks such as diamond.
• Useful exceptions:
  • graphite conducts electricity (non-metal exception), but diamond does not,
  • mercury is a liquid metal at room temperature,
  • bromine is a liquid non-metal at room temperature,

3. Detailed Explanations

A. Physical properties (comparison table)

Malleable means able to be hammered into sheets; ductile means able to be drawn into wires. These describe how a material changes shape, not simply whether it is hard. The table gives typical patterns, not tests that every element must pass.

B. Chemical properties: ions formed (link to bonding)

C. Metallic to non-metallic character across a period

Across a period, elements generally change from metallic → non-metallic character.

For Period 3, the pattern links to valence electrons (outer electrons) in neutral atoms:

4. Common Mistakes

• Replacing the requested property comparison with unrelated advanced trends.
• Saying “non-metals do not conduct electricity” without mentioning the graphite exception.
• Mixing up “cation/anion” wording (metals form cations; non-metals form anions).
• Describing the across-period trend without linking it to the increasing number of outer electrons.

5. Exam Tips

• If asked “why conduct electricity?”: metals conduct due to delocalised electrons; graphite conducts because delocalised electrons can move along its layers.
• For the across-period trend, state both ends: metallic character decreases; non-metallic character increases.

6. Worked Examples

Modelled example 1

Classify and justify

Core

Problem

Classify magnesium as a metal or non-metal and give one physical property that supports the classification.

Study the worked solution

1. State the classification

   Method

   Identify magnesium as a metal.

   Reason

   Magnesium lies on the metallic side of the Periodic Table and shows typical metallic properties.

   Working

   Classification: metal.

2. Select observable evidence

   Method

   Use electrical conductivity or malleability.

   Reason

   Good conduction and ability to change shape without shattering are typical metal properties.

   Working

   For example, magnesium conducts electricity.

3. Write a supported answer

   Working

   Magnesium is a metal because it conducts electricity; malleability would also support the classification.

Guided practice 2

Across-period trend

About 6 min

Problem

Describe and explain the change in character from sodium to chlorine across Period 3.

Connect the trend to outer electrons

Across Period 3

Less metallic, more non-metallicMore metallic, less non-metallicNo change

Outer-electron pattern

IncreasesDecreasesStays at one

Check my attempt

Hints

Hint 1: name both ends

Sodium tends to lose an electron; chlorine tends to gain one.

Hint 2: state both character directions

If metallic character decreases, the complementary non-metallic character increases.

View solution step by step

1. State the character trend

   Method

   Move from sodium towards chlorine.

   Reason

   Elements cross from the metal side towards the non-metal side of the period.

   Working

   Metallic character decreases; non-metallic character increases.

2. Use outer electrons

   Method

   Increase the number of valence electrons across the period.

   Reason

   The simplest stable electron changes shift from electron loss towards electron gain or sharing.

   Working

   Na tends to lose one electron; chlorine tends to gain one.

3. Link explanation to trend

   Working

   Increasing outer-electron count supports the change from metallic to non-metallic behaviour.

Common misconception 3

Conductivity exception

Find and correct the mistake

Learner response

A student says: “Non-metals never conduct electricity, so graphite cannot conduct.” Correct the overclaim and explain graphite’s exception.

Identify the mobile charge carrier

Safe generalisation

Non-metals never conductNon-metals are usually poor conductorsAll non-metals conduct well

Graphite charge carrier

Delocalised electronsMobile carbon ionsMoving molecules

Check my attempt

View solution step by step

1. Correct the absolute claim

   Method

   Replace “never” with a qualified generalisation.

   Reason

   Most non-metals are poor electrical conductors, but graphite is an established exception.

   Working

   Safe claim: non-metals are usually poor conductors.

2. Explain graphite

   Method

   Identify delocalised electrons in its layered structure.

   Reason

   These electrons can move along the layers and carry electrical charge.

   Working

   Mobile delocalised electrons → graphite conducts.

3. State the correction

   Working

   Graphite is a conducting non-metal exception because it has mobile delocalised electrons.

Examiner practice 4

Identify the type of ion

3 marks

Examination question

State the type and charge of ion formed by chlorine, and explain the electron change. [3 marks]

Give classification, charge and electron direction

Write the complete ion explanation

View solution step by step

1. Classify the ion

   1 mark

   Method

   Name an anion or halide ion.

   Reason

   Chlorine is a Group 17 non-metal that forms a negative halide ion.

   Working

   Type: halide anion.

2. State the charge

   1 mark

   Method

   Write Cl⁻.

   Reason

   The ion has one more electron than the neutral atom.

   Working

   Charge: -1.

3. Explain formation

   1 mark

   Method

   Gain one electron.

   Reason

   This completes chlorine’s outer shell.

   Working

   Cl + e⁻ → Cl⁻.

Self-mark with the mark scheme

Compare your response with each mark point. Select a point only when your response contains that evidence.

Self-mark ion type, charge and electron change separately.

Mark points

1. 1 mark: Identifies a halide anion.
2. 1 mark: Gives Cl- or charge -1.
3. 1 mark: States that chlorine gains one electron.

Calculate my mark

Challenge 5

Predict electron behaviour

Minimal support

Position-to-bonding transfer

Unknown element X is in Group 2 and unknown element Y is in Group 17. Predict the ions they form, state the electron change for each, and deduce the neutral ionic formula.

Move from groups to charges to ratio

X ion

X2+X+X2-

Y ion

Y-Y+Y2-

Neutral formula

XYXY2X2Y

Check my attempt

Hints

Hint 1: predict electron direction

Metals on the left lose electrons; Group 17 non-metals gain electrons.

Hint 2: make charge total zero

One 2 + ion needs two 1- ions.

View solution step by step

1. Predict X

   Method

   Remove two outer electrons from Group 2 element X.

   Reason

   Electron loss gives a cation with charge 2 +.

   Working

   X → X²⁺ + 2e⁻.

2. Predict Y

   Method

   Add one electron to Group 17 element Y.

   Reason

   Electron gain completes its outer shell and gives charge 1-.

   Working

   Y + e⁻ → Y⁻.

3. Balance the formula

   Method

   Use two Y ions for each X ion.

   Reason

   1(2 +) + 2(1-) = 0.

   Working

   Neutral formula: XY₂.

Next step

Try Mind Stretcher 1 independently.

7. Mind Stretchers

Mind stretcher 1: Don’t guess the stateExtension

Question: A student writes: “All non-metals are gases.” Correct this with one example.

Show Answer

False. Some non-metals are solids (e.g. carbon, sulfur) and bromine is a liquid at room temperature.

Mind stretcher 2: Use several observationsExtension

Question: Element X is a brittle solid and a poor electrical conductor. Is X more likely metallic or non-metallic? Explain using both observations, and say why the evidence is not conclusive.

Show Answer

X is more likely non-metallic because brittleness and poor electrical conductivity are typical non-metal properties. The evidence is not conclusive: some metalloids, such as silicon, have these properties too. More observations or the element’s identity would be needed for a firm classification.

8. Quiz