Thread: Giant ionic structure

Does a giant ionic structure (compound) always comprise of equal quantites of each atom/ion it is formed of? Is it correct that cations and an anions bond to form a compound of no charge? I say this becuase I saw a diagram of an ionic structure in a book that had one more cation than anions (this has confused me). If a structure were to be like this would it not have a positive charge (rather than no charge)? For a giant ionic structure to have its characteristic 'no charge' would it not need to comprise of equal quantities of each type of ion?
Thanks

There are two separate points to be made here.

Ions can carry a variety of integer charges depending upon how many electrons they lose or gain. Thus Na (sodium) typically carries a +1 charge, through the loss of one electron, Ca (calcium) a +2 charge through the loss of two electrons, and Fe (iron) can be +2, or +3. All that is required is that the net charge be zero.

Very large complex molecules may not even meet this condition. Examples of this are to be found among the clay minerals. These are sheet silicates consisting of linked silica tetrahedra and alumina octahedra, the other ions being oxygens. Silica (+4) can be substituted by aluminium (+3) in the tetrahedra and Calcium (+2) and Magnesium (+2) can substitute in the octahedra.

These substitutions create a charge imbalance which is satisfied in one of two ways. Either cations such as sodium or potassium move into the interlayer space, or water which is bipolar, is attracted positive end first to the clay surface. This is why clays are hydrophilic.

The amount of cations and anions depends on the compound;

in , the ratio would be 2 iron:3 oxygen.

in , there are 2 sodium ions per oxygen ion.

So yes, basically, the ions arrange in such a way that there is no overall charge on the compound.