Question

if during writing a chemical formulae metal is followed by nonmetal then why is sodium acetate written like CH3COONa and not NaCH3COO?

Answer 1

Yes, usually the cation comes first. This is a special case because sodium acetate is an organic compound. In CH3COOH looses it's H+ ion the sodium ion immediately takes its place. Hence CH3COONa 
It's written as CH3COO(-) Na(+)