Structure of an ionic lattice: Sodium Chloride:
Sodium Chloride consists of sodium ions (Na+), each of which is surrounded by six chloride ions (Cl-). In turn,each Cl- ion is surrounded by six Na+ ions. The ions are held together by attractions between these oppositely charged ions. This allows giant ionic lattice to be built up. Similar electrostatic bonds hold all the ionic lattices together. The latice structure of sodium chloridde is aid to be simple cubic. Ionic substances are held together by their opposite electrical charges. Each cation is attracted to several anions and vice versa.
Ionic substances in solution:
Lots of ionic substances dissolve readily in water. When this happens, the ions become surrounded by water molecules.
When sodium chloride dissolves in water, the dissolved ions spread throughout the water randomly. The Na+ and the Cl- ions are separated and are totally independent of each other.
This happens with all ionic substances when they dissolve; the positive and negative ions are separate and behave independently.
Water surrounds ions in the way that it does because it is a polar molecule with a bent shape. The positive hydrogen atoms in water are attracted to negative ions. Water molecules surround the positive ions with the oxygen atoms pointing inwards. Each ion is surrounded by its own sphere of water molecules - this process is known as hydration.
Ions in solution behave independently - and this includes when they are involved in chemicl reactions. If two solution react to form a solid, a precipitate reaction is said to have occured. For Exampe: Na (aq) and NO3 are the spectator ions (they are not invovled in the reaction) and are not included in the ionic equation. Which is: Ag+(aq) + Br-(aq) -> AgBr(s)
Ionic Precipitation Reactions:
The following rule will help you to predict if ionic precipitation reactions will take place when two solutions are mixed:
- all nitrates are soluble in water
- all chlorides are soluble in water except AgCl and PbCl2
- all sulfates are soluble in water except BaSO4, PbSO4 and SrSO4,
- all sodium, potassium and ammonium salts are soluble in water
- all carbonates are insoluble in water except (NH4)2CO3 and those of group 1 elements.
Neutralisation reactions can also be summariesd using ionic equations. When an acid and alkali react, a covalent compound is formed - in this case water. When hydrochloric acid reacts with sodium hydroxide the ions involves, and the products are:
H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) -> H20 (l) + Na+(aq) + Cl-(aq)
When the spectator ions have been removed, the ionic equation is:
H+(aq) + OH-(aq) --> H2O(l)