1.6Unit 1. Structure, Bonding and Introduction to Organic Chemistry

Ionic & Metallic Bonding & Structure — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions

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1.6 Ionic & Metallic Bonding & Structure — IAL EDEXCEL LINEAR (CHEMISTRY) notes: Explain ionic and metallic bonding, the properties of ionic and metallic structures, and the strength of ionic bonds.Ionic bond — the electrostatic attraction between a positive metal ion (cation) an…

Melting and boiling points
Electrical conductivity
Solubility
Electrolysis
Copper(II) chromate(VI)
Electron transfer

Part 1 of 10Giant ionic lattices and their properties

Giant ionic lattices and their properties

Ionic bond

Ionic bond the electrostatic attraction between a positive metal ion (cation) and a negative non-metal ion (anion), acting in all directions.

Lattice

Lattice ions form a giant regular repeating lattice of alternating positive and negative ions.
The lattice type depends on the relative sizes of the ions, with NaCl and MgO cubic.
Electron density maps show the density falls to zero between ions.

Melting and boiling points

Melting and boiling points high, because a lot of energy is needed to overcome the strong electrostatic attraction in the lattice.
Higher ionic charge gives a higher melting point: Na₂O melts at 1405 K and CaO at 2845 K.
Size is not the factor here, because Na⁺ and Ca²⁺ are similar in size.

Electrical conductivity

Electrical conductivity conduct when molten or in solution because ions are free to move.
Solids do not conduct because the ions are fixed in the lattice.

Solubility

Solubility many dissolve in polar solvents such as water.
Polar molecules disrupt the lattice and surround each ion, with the + end towards anions and the - end towards cations.
Ion-dipole attractions hydrate the ions.
Solubility depends on the lattice attraction versus the ion-solvent attraction.
Greater ionic charge generally means lower solubility, as in NaCl (356.9 g dm^-3) and CaCl₂ (74.4 g dm^-3), but there are many exceptions.

Part 2 of 10Evidence for the existence of ions

Electrolysis

Electrolysis positive ions move to the negative electrode and negative ions to the positive electrode.

Copper(II) chromate(VI)

Copper(II) chromate(VI) the olive green solution contains blue Cu²⁺ and yellow CrO₄^2- ions.
On electrolysis blue colour appears at the negative electrode.
Yellow colour appears at the positive electrode.

Part 3 of 10Forming ions and ionic dot-and-cross diagrams

Electron transfer

Electron transfer metals lose valence electrons to form cations and non-metals (right) gain electrons to form anions.
- (left of the Periodic Table)
The ions usually have a full outer shell like a noble gas, as K⁺ and Cl^- are both [2,8,8] like argon.

Ionic bond

Ionic bond the electrostatic attraction between the ions acts in all directions and is strong.
- (non-directional)
The lattice is regular, with positive and negative charges cancelling, so the whole lattice is electrically neutral.

Dot-and-cross diagram

Dot-and-cross diagram shows only outer electrons, with dots for one atom and crosses for the other.
Show the transfer so each ion has a full outer shell.
Draw each ion in square brackets with the charge at the top right.
Use enough atoms to make the total charge zero.

Part 4 of 10Examples of ionic formulae

Calcium fluoride

Ca loses 2 electrons (Ca²⁺) and each F gains 1 (F^-), so CaF₂ needs two fluoride ions.

Lithium nitride

Li loses 1 (Li⁺) and N gains 3 (N^3-), so Li₃N has three lithium ions.

Aluminium oxide

Al loses 3 (Al³⁺) and O gains 2 (O^2-), so Al₂O₃ has two Al³⁺ and three O^2-.

Part 5 of 10Ionic radius, charge density and bond strength

Atomic radius

Atomic radius the distance from the nucleus to the outermost electron, found by halving the distance between the nuclei of two atoms of the same element.
It decreases across a period because the nuclear charge increases while shielding stays the same.

Ionic radius

Ionic radius cations are smaller than their atoms and anions are larger.
Positive ionsfewer electrons feel the same nuclear charge, so a greater charge gives a smaller ion.
Negative ionsextra electrons are held more weakly, so a greater negative charge gives a larger ion.

Isoelectronic ions

N^3-, O^2-, F^-, Na⁺, Mg²⁺ and Al³⁺ all have 1s² 2s² 2p⁶.
More protons pull the electrons closer, so radii fall from N^3- (0.171 nm) to Al³⁺ (0.054 nm).

Charge density

Charge density charge divided by size.
Higher charges and smaller radii give higher charge density, stronger ionic bonds and higher melting points.

Part 6 of 10Polarisation of ions

1Perfect ionic model

Perfect ionic model assumes spherical ions and purely electrostatic attraction.

2Polarisation

Polarisation a cation attracts electrons from the anion and distorts its electron density.
It introduces covalent character, so the measured lattice energy differs from the theoretical value.

3Polarising power of cations

Polarising power of cations increases with charge density.
K⁺ is weaker than Li⁺ because of its larger radius.
Na⁺ is weaker than Mg²⁺ because of its smaller charge.
Small, highly charged cations are the most polarising.

4Polarisability of anions

Polarisability of anions increases with ionic radius.
Br^- is more polarisable than Cl^-.

Part 7 of 10Metallic bonding and the lattice

Lattice

Lattice metal atoms are tightly packed in a giant lattice, often hexagonal layers or a cubic arrangement.

Delocalised electrons

Delocalised electrons outer-shell electrons are free to move throughout the structure and are not bound to one atom.

Metal ions

Metal ions the atoms become positive ions suspended in a sea of delocalised electrons.

Metallic bond

Metallic bond the electrostatic attraction between the positive ions and the delocalised electrons.
It acts throughout the lattice and is non-directional.
It keeps the lattice stable although the positive ions repel one another.

Diagram

Diagram draw layers of close-packed positive ions in a regular arrangement and label the metal ions and delocalised electrons.

Part 8 of 10Strength of metallic bonding

1Stronger metallic bonding

Stronger metallic bonding increases with each of these.
More delocalised electrons per atom.
A higher positive charge on the metal ions.
Smaller metal ions.

2Example

Example melting point rises Na < Mg < Al.

Part 9 of 10Properties of metals

Property	Explanation
High melting and boiling points	Strong attraction between the ions and delocalised electrons in a giant lattice needs much energy to overcome
Good electrical conductors	Delocalised electrons move and carry charge, while the ions stay fixed
Good thermal conductors	Mobile electrons transfer kinetic energy, and vibrating closely packed ions also pass on energy
Malleable and ductile	Layers of ions slide over each other and the delocalised electrons move with them, keeping the attraction so the bonding is not broken

Giant structure
- melting a metal overcomes metallic bonding, not separate molecules.

Part 10 of 10Alloys

Alloy

Alloy formed when atoms of another element, such as carbon in iron, are added to a metal lattice.

Properties

Properties the different-sized atoms stop the layers of metal ions sliding over each other easily, so alloys are stronger and harder than pure metals.

Key terms

Term	Meaning
Cation	A positively charged ion.
Anion	A negatively charged ion.
Charge density	The charge of an ion divided by its size.
Polarisation	Distortion of the electron cloud of an anion by a nearby cation.
Delocalised electrons	Outer electrons free to move throughout a metal lattice.
Metallic bond	The electrostatic attraction between positive metal ions and delocalised electrons.
Isoelectronic ions	Ions with the same electron configuration but different numbers of protons.
Alloy	A metal mixed with atoms of another element, making it stronger than the pure metal.

Avoid these mistakes

Drawing ionic compounds with shared electron pairs — electrons are transferred.

Omitting square brackets and charges on ions in dot-and-cross diagrams.

Saying metal ions carry the current — the delocalised electrons carry the charge.

Saying ionic solids conduct because ions are present — the ions must be free to move (molten or dissolved).

Describing melting of a metal as breaking molecules apart — metallic bonding in a giant lattice is overcome.

Last updated: 12 October 2026