[Byrne]

I've spent some time looking for information on the internet, but all of the sites I come across simply use the terms and do not explain exactly what they mean.  

Another things that is confusing me, my text says that ionic crystals are formed by a 3-D arrangement of positive and negative ions held together by strong, directional bonds, while the information I've found on the net claims that ionic bonds are non directional  

So what 's the difference between these types of bonding and is directional or non directional bonding present in ionic crystals?

[Donaldson Tan]

Ionic bonds involves the electrostatic attraction between opposite-charged ions. imagine a stationery positive charge. when a negative charge is placed in the vincity of the positive charge, there will be attraction between the 2 opposite charged ions. there will be attraction regardless the position of the negative. Hence, ionic bonds are said to be non directional.

In the case of covalent bonds, the bonding electron pair must be between the 2 bonding nuclei. In this sense, the position of the bonding electron pair decides the direction of the covalent bonding.

[Byrne]

Does the arrangement of ions in a crystal lattice account for the directional bonding in ionic crystals?

[Donaldson Tan]

there is no directional bonding between ions inside an ionic lattice.

however, ionic lattic can exhibit directional bonding in a non-direct manner. such directional bonding arises through intramolecular covalent bonds. Eg. there is directional bonding between Nitrogen and Oxygen in the NO₃^- ion.

[Byrne]

Without directional bonding, how can you explain the property of ionic crystals that, when struck with a sharp blow, the crystal will fall apart?

[Donaldson Tan]

The strike displaces the layers within the ionic lattice such that the like-charged ions in adjacent layers are facing each other. This results in repulsion, thus ionic crystal will break.

If directional bonding exists, a strike would not able to displace the ionic lattice.