Hydrogen chloride
The hydrogen has a helium structure, and the chlorine an argon structure.

Covalent bonding at A'level



Cases where there isn't any difference from the simple view



If you stick closely
 to modern A'level syllabuses, there is little need to move far from the
 simple (GCSE) view.  The only thing which must be changed is the 
over-reliance on the concept of noble gas structures.  Most of the 
simple molecules you draw do in fact have all their atoms with noble gas
 structures.



For example:







Even with a more complicated molecule like PCl3, there's no problem.  In this case, only the outer electrons are shown for simplicity.  Each atom in this structure has inner layers of electrons of 2,8.  Again, everything present has a noble gas structure.







Cases where the simple view throws up problems

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