I notice that for quite a few elements, oxygen comes before it in alphabetical order. Here is one of the rules in inorganic chemistry for molecular formulas:
Put all the elements in alphabetical order.
So why do oxides always have what is being oxidized followed by oxygen?
That makes some molecular formulas like PO4 for phosphate violate the rule in inorganic chemistry that the elements are arranged in alphabetical order.
I guess all oxides have some element(except for oxygen or fluorine) followed by oxygen because:
1) it clarifies that what you are talking about is an oxide of that element.
2) the structure of an oxide is always some element with oxygen atoms around it.