Question

Explain the difference between an ionic and a covalent bond by describing how and under what conditions each is formed.

Answer 1

ionic bonds is present between two 'ions' of opposite charge, for achieving stability of there systems, mostly completion of octets.
take Na and Cl (see the eleetronic configuration of both). sodium has 1 extra electron than reqd, for a complete octet, and chlorine 1 less. so what do they do?? chlorine says, "hey mate gimme one electron, and we ll both be stable". sodium thinks replies.. "err i think you 're right!" so sodium gives one electron off to chlorine. now now now... what is the side effect? sodium doesnt realise that because it gave away its one electron, its charge balance between proton and electrons became disturbed and it became positively charged. same for chlorine, it became singly negatively charged. so as an effect, due to electrostatic attraction between the two ions, they get bonded! and thats how a NaCl molecule forms.

now as for a covalent bond, again the same criterion of octet completion is present, albeit ions arent involved. take two oxygen atoms 'O'. both are two short of an octet. so one says two another "hey bro, lets share 2 electrons each, so we ll both have our octets complete. what say?". the other twin says, "ohkay bro!". and they share their electrons, two-a-piece, and get bonded 'covalently'!

Answer 2

and pardon me for the grammatical mistakes and the typos, i typed that out in a real hurry!!