Ionic bonding and ionic latticesEdexcel International A Level Chemistry: Mind map

Exam questions on Ionic bonding and ionic lattices

1. 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
2. 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
3. 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