GCSE · Chemistry · AQA · Spec 8462

Ionic compounds (giant ionic lattice)

Ionic compounds are giant repeating lattices held together by strong attractions between opposite charges.

What you need to know

  • Metals lose outer-shell electrons to form positive ions, while non-metals gain electrons to form negative ions.
  • Oppositely charged ions form a regular giant ionic lattice held by strong electrostatic attractions acting in all directions.
  • Representations of ionic structures can be used to identify ionic compounds and work out empirical formulae, but every model has limitations.
  • Ionic compounds have high melting and boiling points, and conduct electricity when melted or dissolved because their ions can move.

The big picture

Ionic compounds form when metals combine with non-metals and electrons are transferred, producing positive and negative ions. These oppositely charged ions form a regular giant ionic lattice held together by strong electrostatic forces acting in all directions. The many strong bonds give ionic compounds high melting and boiling points. When ionic compounds are melted or dissolved in water, their ions are free to move so charge can flow.

TONIGHT'S REVISION

Ionic compounds (giant ionic lattice)

See how opposite ions build a giant structure and how that structure controls its properties.

From atoms to ions

Metal atomvsNon-metal atom

Track what happens to electrons on each side of the transfer.

Focus

Electron change

Metal atom

Loses electrons from its outer shell.

Non-metal atom

Gains electrons into its outer shell.

The insight

Electron transfer creates the two oppositely charged kinds of ion needed for ionic bonding.

Ion formed

Metal atom

Becomes a positively charged ion.

Non-metal atom

Becomes a negatively charged ion.

Relevant groups

Metal atom

Metals in Groups 1 and 2 form ions whose charge relates to the group number.

Non-metal atom

Non-metals in Groups 6 and 7 form ions whose charge relates to the group number.

Electronic structure

Metal atom

The ion has the electronic structure of a noble gas.

Non-metal atom

The ion has the electronic structure of a noble gas.

How the giant lattice forms

Follow the chain from atoms to structure and then to properties.

Reading ionic-structure models

Different representations help you inspect the same giant structure in different ways.

Core ionic language

These terms connect structure, bonding and properties.

Predict, then check

Use the pattern in the model before revealing the explanation.

A structural diagram shows a regular repeating arrangement of positively and negatively charged ions. What should you deduce?

Key points

1Ionic bonding involves strong electrostatic attraction between oppositely charged ions.
2A giant ionic lattice is a regular structure with attractions acting in all directions.
3Metals lose electrons and non-metals gain electrons when their ions form.
4High melting and boiling points result from the large energy needed to break many strong bonds.
5When melted or dissolved, ions can move and carry charge.

Worked example

Problem

A model of an ionic compound contains 8 X ions and 4 Y ions. What empirical formula does the simplest ion ratio give?

🧠

Memory hook

Lose → positive, gain → negative; opposite ions attract into a giant lattice.

⚠ Watch out

Thinking ionic bonding is just one pair of ions joined together instead of attraction throughout a giant lattice.

✓

Check yourself

Why can an ionic compound conduct electricity when it is melted or dissolved in water?

Flashcards

(11)
What is an ionic compound structurally?
A giant structure of ions held together by strong electrostatic attractions between oppositely charged ions.
What is a giant ionic lattice?
A regular structure of oppositely charged ions with strong electrostatic attractions acting in all directions.
What kinds of elements form ionic compounds?
Metals combined with non-metals.
What happens to electrons when a metal reacts with a non-metal?
The metal loses outer-shell electrons and becomes a positive ion; the non-metal gains electrons and becomes a negative ion.
What electronic structure do ions from Groups 1, 2, 6 and 7 form?
They have the electronic structure of a noble gas, and their charge relates to their group number.
How can a structural diagram help identify an ionic compound?
A regular arrangement of ions can be recognised as a giant ionic structure.
Why must diagrams of ionic lattices be treated carefully?
Dot-and-cross, ball-and-stick, 2D and 3D diagrams are representations, so each has limitations.
How do you work out an empirical formula from an ionic model?
Count each type of ion and reduce the numbers to the simplest whole-number ratio.
Which ionic structure should you be familiar with?
The structure of sodium chloride.
Why do ionic compounds have high melting and boiling points?
Large amounts of energy are needed to break the many strong bonds in the giant ionic lattice.
Why do melted or dissolved ionic compounds conduct electricity?
Their ions are free to move, so charge can flow.

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