Question

What do we mean by directional or non directional nature of bond of a solid? For eg., covalent bonds are considered directional in nature. Does this property define whether a solid is brittle or not?

Answer 1

The meaning of covalent bonds being directional is that atoms bonded covalently prefer specific orientations in space relative to one another. As a result, molecules in which atoms are bonded covalently have definite shapes.
Ionic bond is non-directional, because charge is uniform in all direction. An ion is surrounded by other ion from all the direction. But covalent and coordinate bond are formed by one side only hence are directional.