red asked in Science & MathematicsChemistry · 5 months ago

How do I know when to specify amount of atoms in a molecule in the name?

Heres an example CO2 has 2 oxygen atoms, So in the name "carbon dioxide" we specify that with the "di" part meaning two, but in hydrogen peroxide, we never specified that there are two hydrogens, im confused

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  • 5 months ago
    Best answer

    There is a set of rules for naming compounds. Peroxide defines the oxygen as O2 (2-) (that is why the "per" prefix is there), and given the two minus charge, and the fact that H can give, at most, a +1 charge, the presumption is that the must be two H in hydrogen peroxide.

    A lot of introductory chemistry involves learning the nomenclature rules.

  • Anonymous
    5 months ago

    There is a set of rules for naming compounds. Peroxide defines the oxygen as O2 (2-) (that is why the "per" prefix is there), and given the two minus charge, and the fact that H can give, at most, a +1 charge, the presumption is that the must be two H in hydrogen peroxide.

    A lot of introductory chemistry involves learning the nomenclature rules.

  • 5 months ago

    Naming binary compounds with the Greek prefixes ....

    You can use the Stock system (Named for Alfred Stock) which uses a Roman numeral to specify the oxidation state of the first element in the formula. By the way, the first element in the formula is the one with the lower electronegativity. And the second element's name is modified to end in "-ide."

    The Greek prefix system gives the number of number of atoms in a molecule. The first caveat is avoid the use of "mono" unless it is to distinguish between two similar compounds like carbon dioxide and carbon monoxide. But you would never say "monocarbon dioxide".

    There are a fist-full of possible names for H2O2 in the Wikipedia entry, including dihydrogen dioxide, but the IUPAC approved name is hydrogen peroxide. It's one of those common names of a common compound that has stuck over the years (like water and ammonia). By the way, "peroxide" comes from the O−O linkage of two oxygen atoms in H−O−O−H. The linkage of O−O with a combined oxidation state of -2 is called the "peroxide" ion, O2^2-, and appears in a few other compounds as that same O2^2-.

    As you study chemistry and become familiar with the names of compounds, you will simply remember the names of those common compounds whose names may not follow a convention but are ingrained in the common nomenclature. Those like the aforementioned water, ammonia, and hydrogen peroxide, and many more.

    If you want to have a bit of fun with your chemistry, then take a look at this Wikipedia entry of unusual chemical names:

    https://en.wikipedia.org/wiki/List_of_chemical_com...

    Some are a hoot, but I'm not sure if any, much less all, are officially sanctioned by the IUPAC.

  • david
    Lv 7
    5 months ago

    I will guess that you are in an introductory chem. class. Dr. W gave you a very detailed answer, but probably more than you need. You are probably not studying organic chemistry or you would already have had much of the basic info. My bet is that you only want the basic info.

    ===== At the beginning level .. there are ionic compounds and molecular compounds .. Binary ionic compounds consist of a metal and a nonmetal, like NaCl .. sodium chloride .. no prefixes are used in the names to indicate the number of atoms .. CaF2 is just calcium fluoride. But Binary molecular compounds are the ones that use the prefixes you are talking about. ... CO one oxygen so the name is carbon monoxide

    CO2 has 2 oxygen so it is carbon dioxide

    the first element does NOY use the mono prefix to indicate 1 atom.

    .. but if there is more tan 1 atom then the first element also uses a prefix

    .. Cl2O3 .. both Cl and O are nonmetals so this is not ionic, but is molecular .. 2 = di, and 3 = tri so the name is dichlorine trioxide <<< notice the last element in all these BINARY compounds gets the -ide suffix.

    == That is it. Later you will learn more rules for naming other kinds of compounds ... LEARN THEM AS SOON AS THEY ARE GIVEN. Trying to learn all the rules at one time is just too much to do.

    ==========================================

    some names do not follow these rules .. hydrogen peroxide is an older, common name and does not follow these rules .. Like english spelling rules, there are exceptions and those must just be memorized,

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  • 5 months ago

    your comment doesn't make any sense, you never said why they dont say dihydrogen peroxide.

  • Dr W
    Lv 7
    5 months ago

    first... you're combining several topics here

    .. (1).. "peroxide".. "superoxide".. etc nomenclature

    .. (2).. mono, di, tri - prefix when 2 elements for a series of compounds

    .. (3).. nomenclature of polyatomic particles

    second, chemistry is like learning a foreign language. We have vocabulary, words, terms, structure, etc. To become fluent in it takes years.

    ********

    that said, read through my answer here

    https://answers.yahoo.com/question/index?qid=20160...

    notice the naming scheme? based on the oxidation state of the central atom?

    .. .. oxidation state.. .. .. .. ... .. .acid.. .. .. .. .. .. .. . .. .salt

    .. .. of central atom. . .. .. .. prefix / suffix.. .. .. .. . .prefix / suffix

    .. .. .. .. .lowest.. .. .. . .. ... ..hypo-.. -ous.. . .. .. .. ..hypo-..-ite

    .. .. . . ...higher.. ... .. .. . .. ... .... .... -ous.. . .. .. .. .... .. ... .-ite

    .. .. . . ...higher.. ... .. .. . .. ... .... .... -ic.. .. . .. .. .. .... .. ... .-ate

    .. .. .. .. .highest.. .. .. . .. ... ...per-.. -ic.. . .. .. .. .... .. per-..-ate

    ********

    H2O2... . exists like this.. H - O - O - H

    where

    .. H is +1

    why?

    .. O has the higher "electronegativity" https://en.wikipedia.org/wiki/Electronegativity

    .. so O takes all the electrons from the H's leaving them as +1

    and

    .. O is in the -1 oxidation state...

    why?

    .. the overall H2O2 has no charge.... we know that because when no charge is shown.. we assume 0

    .. each H is +1

    .. each O is identical..

    .. so.. 2x(+1) + 2x(O) = 0 ----> O = -1.. right? 2x(+1) + 2x(-1) = 0?

    and

    .. it's "per" oxide because O's are usually -2 in a compound.. -1 is a "higher" oxidation state

    from this point forward, you should recognize this.. [-O-O-]2-.. . as peroxide

    ... the bond between the O's is the peroxide bond.

    likewise.. [-O-O-]1-.. is "superoxide". as in HO2.. hydrogen superoxide.

    O is in an even higher oxidation state

    **********

    FYI.. you learn this stuff the more you use it. It's not obvious to newbies. don't expect to just know it.

    ********

    ********

    as to carbon dioxide... we use "di" because C and O form a series of compounds

    .. CO.. carbon monoxide

    .. CO2.. carbon dioxide

    .. CO3.. carbon trioxide

    .. C2O.. dicarbon monoxide

    .. C5O2.. pentacarbon dioxide

    and just to toss in a monkey or two

    .. C3O2.. . not tricarbon dioxide.. but "carbon suboxide"

    .. C2O3... oxiranedione... . . .it's named via organic nomenclature systems

    .. C4O6.. .dioxane tetraketone... . ..also organically named

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