Since when do names include numbers?

Copper II Sulfate, Lead IV Oxide, Nickel III Hydroxide...What's with the Roman numerals in those names for chemical compound?

Some elements can only have one charge, so you can just use their name without needed to add anything to explain what the charge is. Sodium is always 1+ charge, so you can just name the compounds sodium chloride, sodium oxide, etc.

But some elements can have different charges at different times. Copper is sometimes 1+ and sometimes 2+, so you can't just call something copper oxide. You wouldn't know if that was CuO or Cu2O becuase you wouldn't know what charge to criss-cross. So we use a Roman numeral in the name to show what charge the metal has in this particular substance.

So CuO would be copper II oxide and Cu2O would be copper I oxide. Remember that the Roman numeral doesn't tell us what the subscripts are, they tell us the charge. It's easy to get confused and get the names backwards.

So which elements need these Roman numerals? All of the transition metals except for zinc, cadmium and silver can have more than one charge and need Roman numerals. Those three always have the same charge (silver is 1+ and zinc and cadmium are 2+) so they don't need Roman numerals. Also tin and lead, even though they aren't transition metals, can have 2+ or 4+ charges and need Roman numerals.

Ionic, covalent, polyatomic...are those even real words?

Listening to a science class can really sound like a foreign language sometimes. It's like people tried to come up with the most confusing words they could think of. And then they used other complicated words to describe the first set of complicated words (like stoichiometry? even the spell-check thinks the word is made up).

And then they want you to name the compounds. And if you try to give them nice names like Buttercup or Hugo they don't give you any credit at all... They want you to follow a very confusing set of rules just to give the simple looking symbols long confusing names. Nitrogen triiodide (which by the way is so explosive it will ignite it touched by a feather) has a name that looks like it can't possibly be real, or at least must be spelled wrong. Who puts two "i"s in a row in a word anyways.

The rules don't really have to be that complicated if you break it down in to pieces. First you have to figure out if the compound you have is ionic or covalent (there are also acids, organic compounds and other special compounds, but that is for a different post).

Remember that an ionic compound is made of one positive and one negative ion. That almost always means one metal and one nonmetal. The only common exceptions are hydrogen, which can act like either a nonmetal or a metal depending on the situation, and the polyatomic ions which are a dead giveaway that you have an ionic compound. Hydrogen you can name like a metal in simple compounds.The polyatomic ions each have a special name, like sulfate or hydroxide, and they keep that name in the compound.

Ionic compounds are named by giving the name for metal followed by the name of the nonmetal.

• Ending of the nonmetal is changed to -ide (oxygen becomes oxide, chlorine becomes chloride)
• Polyatomic ions keep their -ite and -ate endings
• If the metal can have more than one charge[transition metals plus tin and lead, minus silver, cadmium and zinc], include the Roman Numeral for the charge it has in that compound
  

Covalent compounds are made of only nonmetals. Since they can go together in more than one combination (N2O, NO2, N2O3) you can't just use the element names, no one would know which nitrogen oxide you had. So we use prefixes, or extra letters in front of the name, to show how many of that element are in the particular element you are trying to name right now.

So N2O would be dinitrogen monoxide, di- meaning 2 for the two nitrogens, and mono- meaning 1 for the one oxygen. NO2 would be nitrogen dioxide, notice that it isn't mononitrogen. One of the goofy things with the prefixes is that is if the first element is only one, they don't include the mono-, but if the second element is one they do.

Why do Acids have to have funny names anyways?

So why is HCl hydrochloric acid instead of just plain old hydrogen chloride? Well, it is so that Chemistry teachers can torture their students by making them learn yet another different set of rules for naming stuff.

Well not really, but it might seem like that. And you actually have to know how to do it even if the only reason is a tortuous teacher (tortuous: adjective - not direct or straightforward; one who tortures) so you may as well try to get the rules figured out.

The naming rules are all based on the anion in the chemical formula for the acid. Remember the anion is the negative part so it will always come second. And the anion might be just one element, like in HCl or H2S. Or it might be a polyatomic ion like in HNO3 or H3PO4. The ending of the name of the anion tells you how the acid will be named.

Three rules:

1. anion ends in "ide" the acid will be named hydro_____ic acid

• HCl, anion is chloride, acid name is hydrochloric acid
• H2S, anion of sulfide, acid name if hydrosulfuric acid

2. anion ends in "ite" the acid will be named ______ous acid

• HNO2, anion is nitrite, acid name is nitrous acid
• H2SO3, anion is sulfite, acid name is sulfurous acid

3. anion ends in "ate" the acid will be named _______ic acid

• H2CO3, anion is carbonate, acid name is carbonic acid
• H2SO4, anion is sulfate, acid name is sulfuric acid

But WHY do they have these confusing naming rules that seem to just be made up out of nowhere? It's based on an older system of naming that used name suffixes instead of number to give information about the compound. The compounds that we use Roman Numerals to name used to use -ous and -ic endings instead to show which charge the metal had in that compound. The larger of the 2 possible charges got the -ic ending and the smaller got the -ous ending. So instead of Hg II chloride it would have been mercuric chloride.

Anyways, acids still use this older naming system with the different endings telling you what to put in the formula.