Ionic Structures Worksheet printable pdf download

C h e m g u i d e – a n s w e r s

GIANT IONIC STRUCTURES

1. a)

It doesn't matter which ion ends up in the centre of the

structure (it could just as well be a chloride ion), but

your ions must alternate in each of the three

dimensions. You must include a key, and it helps if

you remember, and show, that chloride ions are bigger

than sodium ions.

b) Each sodium ion is touching 6 chloride ions, and each chloride ion is touching 6 sodium ions.The

lines in the sketch show which ions are touching each other. The sodium ion in the centre is being

touched by 6 chloride ions. The diagram shows that a chloride ion in the centre of each face is

being touched by 5 sodium ions in this bit of structure, plus another one as the structure continues

making 6 in all. (Or words to that effect. It certainly wouldn't be worth spending time in an exam

drawing a second diagram with a different ion in the centre just to make this point.)

2. a) Each caesium ion is touching 8 chloride ions, and each chloride ion is touching 8 caesium ions.

Diagrams you could use include:

and

If you used the left-hand version, you need only draw perhaps 9 (or even just 4) ions in the base

layer, and don't forget to point out that the next layer would look exactly the same as the bottom

layer with a repeat of the caesium layer on top of that. If you use the right-hand one, don't forget to

say that the pattern would be exactly the same if the ions were swapped so that you had a chloride

ion in the middle with caesium ions around it.

b) Caesium ions are bigger than sodium ions, and you can fit eight chloride ions around a caesium

ion without the chloride ions touching. If you try to fit eight chloride ions around a sodium ion,

they would touch, and therefore repel. Repulsion reduces the stability of the structure.

3. Melting and boiling points depend on the attractions between the ions. In MgO, 2+ magnesium

ions are attracting 2- oxide ions. These attractions will be much stronger than those between 1+

sodium and 1- chloride ions.

Ionic Structures Worksheet