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
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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
Section 1 of 11The 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.
Section 2 of 11Electrical 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.
Section 3 of 11Malleability, ductility and strength
Malleable
- Malleable can be hammered into sheets.
Ductile
- Ductile can be drawn into wires.
1
A force is applied to the metal.
2
Layers of positive ions slide past one another.
3
Delocalised electrons move with the ions, keeping the attraction in all directions.
4
No like-charge repulsion arises between layers, unlike in ionic lattices.
5
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.
Section 4 of 11Other 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).
Section 5 of 11What 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.
Section 6 of 11Melting 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.
Section 7 of 11Uses 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.
Section 8 of 11Comparing 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 |
Section 9 of 11More 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.
Section 10 of 11Key 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. |
Section 11 of 11Exam technique
1
Saying metals conduct only because of positive ions — conduction is by mobile delocalised electrons.
2
Saying melting point rises down group 1 — it falls as the cation radius increases.
3
Saying delocalised electrons belong to one atom — they are shared throughout the lattice.
4
Explaining malleability by broken bonds — the non-directional bond is maintained as layers slide.
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