S2.3Structure 2 — Models of bonding and structure

The metallic model — IB Chemistry SL Revision Notes & Topical Questions

5 min read 11 parts Lesson 3 of 6 1 quiz

📚 IB Chemistry SL Hub / Topical Revision

0%read

Lesson summary

S2.3 The metallic model — IB CHEMISTRY SL notes: Describe the metallic bond, explain the properties of metals and explain trends in melting point.Structure — metal atoms lose their valence electrons, which become delocalised, and the positive ions sit in fixed positions in a regu…

Lattice stability
Electrical conduction
Both states
Across a period
Thermal conduction
Strength and hardness

Part 1 of 9The metallic bond

The metallic bond

Structure

Structure metal atoms lose their valence electrons, which become delocalised, and the positive ions sit in fixed positions in a regular lattice.

Metallic bond

Metallic bond the electrostatic attraction between the lattice of positive ions and the sea of delocalised electrons.

Direction

Direction the bond acts in all directions, so it is non-directional.

Lattice stability

Lattice stability the positive ions repel each other, which keeps the lattice arranged.

Part 2 of 9Electrical and thermal conductivity

Electrical conduction

Electrical conduction when a potential difference is applied, delocalised electrons drift towards the positive terminal and carry charge.

Both states

Both states metals conduct as solids and as liquids because the electrons are mobile in both.

Across a period

Across a period more outer electrons give more delocalised charge carriers.
- (Na 1, Mg 2, Al 3)

Thermal conduction

Thermal conduction vibrating cations pass energy to neighbours and to the delocalised electrons,
- which carry the kinetic energy rapidly through the metal.

Part 3 of 9Malleability, ductility and strength

Malleable

Malleable can be hammered into sheets.

Ductile

Ductile can be drawn into wires.

A force is applied to the metal.

Layers of positive ions slide past one another.

Delocalised electrons move with the ions, keeping the attraction in all directions.

No like-charge repulsion arises between layers, unlike in ionic lattices.

The metal changes shape without fracturing.

Strength and hardness
- metals are typically strong and hard because of the strong attraction and the closely packed ions.

Part 4 of 9Other physical properties

1Melting and boiling points

Melting and boiling points generally high because much energy is needed to overcome the strong attraction throughout the giant lattice.

2Density

Density metals are usually dense because the ions are closely packed.

3Lustre

Lustre arises from the interaction of delocalised electrons with light.

4Exceptions

Exceptions mercury is the only metal liquid at room temperature (m.p. −39 °C) and tungsten has the highest melting point (3422 °C).

Part 5 of 9What determines the strength of metallic bonding

Charge of the ion

Charge of the ion a higher charge means more delocalised electrons per atom and a stronger attraction.

Radius of the ion

Radius of the ion smaller cations attract the delocalised electrons more strongly.

Charge density

Charge density the ratio of charge to size, and higher charge density gives stronger bonding.

Melting point link

Melting point link stronger metallic bonding needs more energy to break the lattice, so the melting point is higher.

Part 6 of 9Melting point trends in s and p block metals

Trend	Metals	Melting point / K	Explanation
Across period 3	Na, Mg, Al	371, 922, 933	Charge rises from +1 to +3 and the cation gets smaller, so bonding strengthens
Down group 1	Na, K, Rb	371, 337, 312	Same charge but larger cations, so attraction to the electrons weakens
Group 1 as a whole	Li to Cs	Decreases	Only one delocalised electron per atom, with increasing cation radius

Period 3 limit

Period 3 limit only Na, Mg and Al have metallic bonding in the period 3 melting point graph.

Trends not rules

Al melts only slightly above Mg, and packing structure can also matter, though only the broad trends are needed.

Part 7 of 9Uses of metals

Selection

Selection a metal is chosen by properties such as malleability, melting point, density, reactivity, conductivity, strength, toxicity, corrosion resistance and strength-to-weight ratio.

Aluminium

Aluminium used for food cans because it is non-toxic and resists corrosion and acidic foods.

Copper

Copper used for electrical wiring because it is a good conductor and is malleable and ductile.

Stainless steel

Stainless steel used for cutlery because it is strong and corrosion resistant.

Part 8 of 9Comparing bonding models

Feature	Ionic	Covalent network	Metallic
Particles	Cations and anions	Atoms	Cations and delocalised electrons
Conductivity as solid	No	No (except graphite)	Yes
Conductivity as liquid	Yes	No	Yes
Behaviour under stress	Brittle	Hard and brittle	Malleable and ductile

Part 9 of 9More from the specification

1Metallic bonding architecture

Strong electrostatic forces of attraction between positively charged metal centres and delocalised valence electron clouds.

2Factors affecting metallic bond strength

Ionic charge density of metal centres and the number of delocalised electrons per atom determine melting points and hardness.

3s-block vs transition block elements

Transition metals form stronger metallic bonds than s-block metals due to delocalisation involving both 3d and 4s electrons.

4Malleability and ductility

Layers of metal ions can slide over one another under shear stress without shattering because delocalised bonding remains non-directional.

5Element

A substance made of only one type of atom.

6Electrostatic force

Force of attraction between opposite charges.

Key terms

Term	Meaning
Metallic bond	The electrostatic attraction between positive metal ions and delocalised electrons.
Delocalised electrons	Valence electrons not tied to one atom that move freely through the metal.
Malleability	The ability to be hammered into shape without breaking.
Ductility	The ability to be drawn into wires without breaking.
Charge density	The ratio of ionic charge to ionic size.
Lustre	The shiny appearance of metals caused by delocalised electrons interacting with light.

Avoid these mistakes

Saying metals conduct only because of positive ions — conduction is by mobile delocalised electrons.

Saying melting point rises down group 1 — it falls as the cation radius increases.

Saying delocalised electrons belong to one atom — they are shared throughout the lattice.

Explaining malleability by broken bonds — the non-directional bond is maintained as layers slide.

Last updated: 14 October 2026