Structure of an ionic lattice: Sodium Chloride
Sodium Chloride consists of sodium ions (Na+) surrounded by six chloride ions (Cl-).
Held together by electrostatic attractions by oppositely charged ions.
Forms giant ionic lattice, noted as simple cubic.
Water of Crystallisation
Some ionic crystals contain water molecules. These sit within the ioic lattice and are known as water of crystallisation, the crystal is hydrated.
If two solutions react to form a solid a precipitate is formed.
Ag+(aq) + NO3-(aq) + Na+(aq) + Br-(aq) --> AgBr(s) +Na+(aq) + NO3-(aq)
Na+(aq) and NO3-(aq) are spectator ions so not in final equation:
Ag+(aq) + Br-(aq) --> AgBr(s)
All silver halides are insoluble.
Hydration of Ions in Aqueous solution.
Many ionic compounds dissolve in water, whether ornot depends on the energy changes involved.
1. ion separation
2. ion hydration (surrounding ions by water molecules)
The electrostatic attractions between oppositely charged ions are overcome by the small charge on a water molecule. Water is made up from hydrogen and oxygen which have different electronegativities.
The negative end of a water dipole is attracted to a positive ion in the lattice and pulls it away. It is then surrounded by other water molecules that align themselves around the positively charged ion with the negative dipole facing it.
Vice versa for the negative ions!
The ions are said to be hydrated.