What happens to a purple MnO₄⁻ ion on damp filter paper between electrodes?

It migrates towards the positive electrode, showing it is a negatively charged ion.

What does an electron density map of NaCl show?

Separate, almost circular regions of electron density round each ion, with almost zero density between them.

Define ionic bonding.

The strong net electrostatic attraction between oppositely charged ions throughout a giant lattice.

Why do solid ionic compounds not conduct electricity?

The ions are fixed in the lattice and cannot move to carry charge.

Why do molten ionic compounds conduct?

The ions are free to move and carry the charge.

How are ions shown in a dot-and-cross diagram?

In square brackets with the charge outside, showing the outer shell with a full set of electrons.

Why does MgO have a higher melting point than NaCl?

Mg²⁺ and O²⁻ have twice the charge and are smaller, so the attraction is much stronger.

How does ionic radius affect the strength of ionic bonding?

Smaller ions get closer together, so the electrostatic attraction is stronger.

What does isoelectronic mean?

Having the same number of electrons and the same configuration.

What is the trend in radius from N³⁻ to Al³⁺?

It decreases, because nuclear charge rises from 7 to 13 protons while the 10 electrons and shielding stay the same.

Why does ionic radius increase down a group?

Each ion has an extra electron shell, so the outer electrons are further from the nucleus and more shielded.

Ionic bonding and ionic latticesEdexcel International A Level Chemistry: Flashcards

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Give three types of evidence that ionic compounds contain ions.

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Give three types of evidence that ionic compounds contain ions.: Physical properties (high melting point, conducts when molten), migration of coloured ions towards an electrode, and electron density maps.
What happens to a purple MnO₄⁻ ion on damp filter paper between electrodes?: It migrates towards the positive electrode, showing it is a negatively charged ion.
What does an electron density map of NaCl show?: Separate, almost circular regions of electron density round each ion, with almost zero density between them.
Define ionic bonding.: The strong net electrostatic attraction between oppositely charged ions throughout a giant lattice.
Why do solid ionic compounds not conduct electricity?: The ions are fixed in the lattice and cannot move to carry charge.
Why do molten ionic compounds conduct?: The ions are free to move and carry the charge.
How are ions shown in a dot-and-cross diagram?: In square brackets with the charge outside, showing the outer shell with a full set of electrons.
Why does MgO have a higher melting point than NaCl?: Mg²⁺ and O²⁻ have twice the charge and are smaller, so the attraction is much stronger.
How does ionic radius affect the strength of ionic bonding?: Smaller ions get closer together, so the electrostatic attraction is stronger.
What does isoelectronic mean?: Having the same number of electrons and the same configuration.
What is the trend in radius from N³⁻ to Al³⁺?: It decreases, because nuclear charge rises from 7 to 13 protons while the 10 electrons and shielding stay the same.
Why does ionic radius increase down a group?: Each ion has an extra electron shell, so the outer electrons are further from the nucleus and more shielded.

Exam questions on Ionic bonding and ionic lattices

A student lays a strip of filter paper, soaked in aqueous sodium nitrate, between two electrodes connected to a 20 V d.c. supply. A single crystal of potassium manganate(VII), KMnO₄, is placed in the middle of the strip. After 20 minutes a purple band has spread along the paper towards the electrode connected to the positive terminal, while the rest of the paper remains colourless.
Explain why this experiment provides evidence that potassium manganate(VII) contains ions.2 marks
Electron density maps of sodium chloride, made using X-ray diffraction, show contour lines of electron density. The contours form separate, almost circular patterns around the sodium and chlorine nuclei, and the electron density falls to almost zero in the region between the two kinds of ion.
Explain what the electron density map shows about the bonding in sodium chloride.2 marks
Calcium fluoride, CaF₂, occurs naturally as the mineral fluorite and is used to make windows for infrared spectrometers. Calcium has atomic number 20 and fluorine has atomic number 9. Solid calcium fluoride does not conduct electricity, but it does conduct when molten, and its melting point is 1418 °C.
Describe, in terms of electrons, how calcium atoms and fluorine atoms form calcium fluoride.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).