chemistry structural formula

It is O=C=S

since O and S has 6 outermost electron
they need 2 more electron,
so then need one double bond or 2 single bond

for C, C has 4 outermost electron
it needs 4 more elctron,
it needs a total 4 bonding

So, it is O=C=S

The structural formula is S=C=O , not the others . COS is called Carbonyl Sulfide .

2011-10-11 15:50:40 補充：
不可以寫成C=O=S , 因為O cannot form 4 bonds ,2 with C & 2 with S .