# How to remember/write molecular formulas?

For example, when given the reactants and asked to write a complete formula including their products for nitrogen and oxygen...:

$\ce{N2 + O2 -> 2NO}$ (this is the correct one right)

but what naturally comes to mind is that I know what will be formed in this case as in: $\ce{N2 + O2 -> NO}$ ( how am I suppose to know that there is 1 "O"s or that there is only 1 N!!)

Ok example two!! The desolation of nitrogen dioxide in water(acid rain and stuff): $\ce{NO2 + H2O -> H+ + NO3- + HNO2}$ ( correct version)

alright right here, I know that an acidic oxide + water gets you oxyacid the $\ce{HNO2}$right. But how in the world was I suppose to know $\ce{H+}$ and $\ce{NO3-}$ would be there??

So basically, is there like no way to find what the products will be without doubt with only knowing some basic rules(such as the products of an acidic oxide and water and others) or with electron configuration in example one. Or is the only way, just to remember the whole formula.

• There are definitely some rules. Read a book on inorganic chemistry :-) I think the one by Housecroft and Sharpe is the standard at the moment, but would love to hear other suggestions. I personally found organic chemistry more easy to swallow, but honestly would recommend a good foundation of inorganic chemistry as well. – Brian Mar 19 '16 at 7:01
• Chemistry doesn't have the same sort of predictive powers as physics or math, but there sure are some rules. Experience helps too. I'd suggest JD Lee..it is good for inorganic chemistry(especially chemical bonding). As @Brian mentioned, organic chemistry is a bit more logically convincing; LG Wade or Morrison-Boyd are good books if you want to have a go. – GRrocks Mar 19 '16 at 10:17