Mini Chemistry
Part of Mini EducationSwitch subject

Metals and Non-Metals

Compare metals and non-metals, link outer electrons to ion formation, and apply the metallic-to-non-metallic trend across a period.

  • SEC G3 Pure Chemistry 2027
On this page

Learning objectives

  • describe the relationship between number of outer (valence) electrons and the ionic charge of an ion for the first twenty elements
  • describe the change from metallic to non-metallic character from left to right across a period of the Periodic Table
  • describe the relationship between number of outer (valence) electrons and metallic/non-metallic character

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.

Typical properties of metals and non-metalsMetals are typically good conductors, malleable, ductile and form positive ions by losing electrons. Non-metals are typically poor conductors, brittle when solid and form negative ions or covalent substances. Graphite conducts electricity, mercury is a liquid metal and bromine is a liquid non-metal.Metals and non-metals: observations and particlesTypical metals• good electrical and thermal conductors• malleable and ductile• usually solid at room temperatureParticle change: lose electronsM → Mⁿ⁺ + ne⁻positive ions (cations) formTypical non-metals• poor electrical and thermal conductors• brittle when solid; not ductile• may be solid, liquid or gasParticle change: gain or share electronsX + ne⁻ → Xⁿ⁻anions or covalent substances formUseful exceptionsgraphite conducts electricity · mercury is a liquid metal · bromine is a liquid non-metal
Use typical properties to compare classes of elements, then qualify the comparison with a named exception only when it is relevant.

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 an element that typically forms negative ions (anions) or shares electrons (covalent bonding) and is usually a poor electrical conductor.

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 form covalent molecules.
  • 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

Quick Recall (properties + ions)
  • Metals usually lose electrons to form cations (e.g. Na⁺, Mg²⁺).
  • Non-metals usually gain electrons to form anions (e.g. Cl⁻, O²⁻) or form covalent molecules.
  • Across a period, character changes from metallic to non-metallic as the number of outer electrons increases.
  • Key exceptions to broad physical-property patterns: graphite conducts; mercury is a liquid metal; bromine is a liquid non-metal.

A. Physical properties (comparison table)

PropertyMetalsNon-metals
appearanceshiny (lustrous)dull
strengthusually strongusually weak/brittle (if solid)
malleable/ductileyesno (brittle if solid)
state at room tempmostly solid (except mercury)many are gases; some solids; bromine is liquid
electrical conductivitygoodpoor (except graphite)
thermal conductivitygoodpoor (generally)
Two useful exceptions
  • Graphite is a non-metal but conducts electricity (delocalised electrons).
  • Mercury is a metal but is liquid at room temperature.
Element typeElectron behaviourIon formed (typical)Example
metalslose electronscationsNa → Na⁺ + e⁻
non-metalsgain electronsanionsCl + e⁻ → Cl⁻
Bonding explains the table

Metals form ionic compounds with non-metals: Ionic Bonding.
Many non-metals form covalent molecules: Covalent Bonding.

C. Metallic to non-metallic character across a period

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

This links strongly to valence electrons (outer electrons):

Valence electrons (main-group)Typical character (O-Level)
1–3metals (lose electrons to form cations)
4often covalent behaviour; carbon and silicon do not usually form simple ions
5–7non-metals (gain/share electrons)
full outer shell (Group 18)very unreactive non-metals (noble gases)
Use the stated evidence

If an unfamiliar element has mixed properties, classify it from the observations supplied rather than relying only on its position.

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

How to answer comparison questions

State the requested contrasting properties first. Add a named exception only when it is relevant to the question.

  • If asked “why conduct electricity?”: metals conduct due to delocalised electrons; graphite conducts due to delocalised electrons between 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
Outer-electron pattern

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
Graphite charge carrier

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

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⁻.

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
Y ion
Neutral formula

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.

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. Its oxide reacts with an alkali. Is X more likely metallic or non-metallic? Explain using both observations.

Show Answer

X is more likely non-metallic. Brittleness and poor conductivity are typical non-metal properties, while reaction of its oxide with an alkali suggests an acidic oxide, which is typical of non-metals.

8. Quiz

Quiz Time!

Test typical properties, ion formation, useful exceptions and the metallic-to-non-metallic trend.

Go to Quiz Page