Subject: How can dissociation of salt when dissolving not be a chemical change?

I have been explaining to my eighth grade students that it is clear that 
dissolving is a physical change because although you can't see salt when it 
dissolves in water, you can taste it.  Also, if the salt molcules broke apart 
you would get atoms of sodium which explodes in water, and chlorine gas which 
is a poisonous gas.  Now I am reading further in my (new) text and reading that 
NaCl molecules "dissociate" when they dissolve.  How is this different from 
breaking the NaCl molecules apart into sodium metal and chlorine gas?  Any 
suggestions on how to explain this to eighth graders?

Re: How can dissociation of salt when dissolving not be a chemical change?