There is a tendency to put the positive ion (or the element that acts as a donor of electrons) first so Na trumps Cl for first place - also why water is H2O and not, say, HOH. As you advance through chemistry you'll find there are lots of equivalent ways of writing out chemical names.
The only specific reason is that IUPAC defined naming rules so that when we talk about compounds we can name them in a way that is unique and unambiguous.
Not that all names assigned using IUPAC rules are unique and unambiguous, as the rules evolved with time, so some older publications can use different names than the current ones.
#4
chill_factor
898
5
yes its the same thing lol. in general elements commute unlike operators in QM.
this works only for elements though. in polymers and in anisotropic materials order of the constituents matters.