The known oxides of nitrogen are NO, NO2, NO3 (unstable), N2O, N2O3, N2O4, N2O5, and N2O6 (also unstable). Strictly speaking, nitrogen tetroxide would be NO4 (even though it doesn't actually exist as far as I know), so your teacher is right about that. It is perfectly correct to say, "Nitrogen tetroxide (meaning NO4) is an unstable molecule not known to exist." Unfortunately these names are often used carelessly, with people calling N2O4 "nitrogen tetroxide" when they should really call it dinitrogen tetroxide. A Google keyword search on "nitrogen tetroxide" gives hits mostly for N2O4. (Sometimes NO4 is mentioned specifically, but I'm not so sure about that!)
There is a Wikipedia encyclopedia entry for "nitrogen tetroxide". It says (with some typos),
Nitrogen tetroxide
From Wikipedia, the free encyclopedia.
Nitrogen tetroxide (N2O4) is a hypergolic propellant often used in combination with a hydrazine-based rocket fuel. Nitrogen tetroxide is an oxidizer and highly toxic and corrosive. When it is combined with water the resultant is nitric acid. It is also called dinitrogen tetroxide.
And,
Talk:Nitrogen tetroxide
From Wikipedia, the free encyclopedia.
According to the rules for naming chemical elements, the name that this article designates the element at indicates NO4 (one nitrogen and 4 oxygen.)Does NO4 exist?? It can't! The reason is:
The oxidation number for oxygen is -2. To cancel out the 4 oxygen atoms, the nitrogen has to be 4 * 2 = 8. Nitrogen can have an oxidation number of +5, and so 8 is too large. The following compounds exist:
- N2O: Dinitrogen monoxide
- NO: Nitrogen monoxide
- N2O3: Dinitrogen trioxide
- NO2: Nitrogen dioxide
- N2O5: Dinitrogen pentoxide
>> In water this would be hydrosulfuric acid right? <<
That's normally the case. In aqueous solution, H2S is a weak acid, so it is usually appropriate to use the acid name in this context.
>> Also how do you know when to treat H as a metal or non metal when naming compounds? <<
With the most active metals (Group IA and IIA) hydrogen can form ionic hydrides in which it is more energetically favorable for H to be the negative ion. In any ionic compound the positive ion is always named first and the negative ion second. In NaH and similar hydrides, the hydrogen is the negative ion. In binary molecular compounds like HCl, the rule is to name the less electronegative element, which has a "partial" positive charge (d+), first, and the more electronegative element, which has a partial negative charge (d-), is named second analogous to the way ionic compounds are named. When dissolved in water, HCl actually is in the form of H+ and Cl- ions. In the case of NaH, a table of electronegativities also tells us that H is the more electronegative element.
Names like "water", "hydrogen peroxide", and "ammonia" are common names of these substances and as such are normally used in place of "dihydrogen monoxide", dihydrogen dioxide", and "trihydrogen nitride". One more note - Organic hydrocarbons such as CH4 and C2H6 (methane and ethane) have their own special names and naming rules, different from that described above.
>> Do most semi-metals and non-metals, when combined, make molecular compounds? <<
That's correct. Examples would be SiCl4 and GeCl4 which are molecular.
Hope all this isn't too confusing!
Steve
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