先写C和H,其他元素按照字母表顺序就好,一般是C,H,Br,Cl,F,I,N,O,P,S. 参考Hill system. The Hill system (or Hill notation) is a system of writing empirical chemical formulae, molecular chemical formulae and components of a condensed formula such that the number of carbon atoms in a molecule is indicated first, the number of hydrogen atoms next, and then the number of all other ...