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Chemical Nomenclature

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    A) Nomenclature for Binary (two elements) Compounds

    1. Nomenclature for Nonmetal-Nonmetal* (not the same as that for Metal-Nonmetal)

    a) Use prefix to indicate how many of each of the elements there are, and change the ending of the last element to -ide.
    Number Prefix** Number Prefix** Number Prefix**
    1 mono-,mon- 4 tetra-, tetr- 7 hepta-. hep-
    2 di- 5 penta-, pent- 8 octa-, oct-
    3 tri- 6 hexa-, hex- 9 nona-, non-
    **The final a or o in a prefix is left off when the first letter of the element is an a or o, as in tetroxide (rather than tetraoxide,) but triiodide, not triodide.
    b) Examples: nitrogen monoxide, NO (if there is no prefix on the first element, then it is understood to be mono, this is not true for the second element); N2O, dinitrogen monoxide; dinitrogen trioxide, N2O3; trinitrogen tetroxide, N3O4; tetranitrogen trioxide, N4O3.

    2. Nomenclature for Metal-Nonmetal

    a) The net charge [the sum of all the Oxidation States (ox. st.)] in a molecule must equal zero, the ending of the last element is changed to -ide, and if the metal has more than one common charge, the charge must be given as part of the name.

    ***Rules for Assigning The Oxidation State (or Oxidation Number) (the charge) for Atoms
    Memorize and apply in order! Example, if there is a choice, rule 3 is applied before rule 4, 4 before 5, etc.

    1. Free elements in their natural form (uncombined with other elements) are assigned an oxidation state (ox. st.) of 0. (e.g. Fe(s), O2(g)...)
    2. The sum of the ox. st. of all the atoms in a species (molecule, ion, isolated atom, or formula unit) must be equal to the net charge on the species.
    3. Group(1 or I) elements, and Ag are assigned an ox. st. of +1 (e.g Li+, Na+, K+......etc)
    4. Fluorine in a compound is assigned an ox. st. of -1 (e.g. F-)
    5. Group(2 or II) elements, and also Zn and Cd are assigned an ox. st. +2 (e.g. Be+2, Mg+2 , Ca+2.....etc)
    6. Hydrogen in a compound is assigned an ox. st. of +1.
    7. Oxygen in a compound is assigned and ox. st. of -2.

    ***These rules are related to electronegativities (electronegativity is how much an atom wants to be the negative partner in a polar bond).

    Some other useful Oxidation States to know

    • Group(3 or III)) elements tend to form +3 ions, e.g. Al+3, Ga+3......etc
    • Group(17 or VII) elements tend to form -1 ions, e.g. F-, Cl-, Br-......etc
    • Group(16 or VI) elements tend to form -2 ions, e.g. O-2,S-2.....etc
    • Group(15 or V) elements tend to form -3 ions, e.g. N-3,P-3......etc

    b) Examples:

    • calcium oxide, CaO (rule 5 Ca+2, and rule 7 O-2 ; Total charge: (+2) + (-2) = 0)
    • lithium oxide, Li2O ( rule 3 Li+, and rule 7 O-2 ; Total charge: (+1)x2 + (-2) = 0)
    • magnesium fluoride, MgF2 (rule 4 F-, rule 5 Mg+2 ; Total charge: (+2) + (-1)x2 = 0)

    Transition and many other Metals have more than one common ionic charge. (Some do not as Zn+2,Cd+2, Ag+)
    Here are some common metals which have more than one common ionic charge
    Metal Ionic Charge Symbols Modern (systematic) Names

    • Chromium +2 and +3 Cr+2, Cr+3 Chromium(II), Chromium(III)
    • Cobalt +2 and +3 Co+2, Co+3 Cobalt (II), Cobalt (III)
    • Copper +1 and +2 Cu+, Cu+2 Copper (I), Copper (II)
    • Gold +1 and +3 Au+, Au+3 Gold (I), Gold (III)
    • Iron +2 and +3 Fe+2, Fe+3 Iron (II), Iron (III)
    • Mercury +1 and +2 Hg2

    +2(yes), Hg+2 Mercury (I), Mercury (II)
    Tin +2 and +4 Sn+2, Sn+4 Tin (II), Tin (IV)
    Thallium +1 and +3 Tl+, Tl+3 Thallium(I), Thallium(III)

    Metals that do not have more then one charge are only groups I and II , Zn+2,Cd+2, Ag+ and Al and Ga from group 13 (or III), which are +3. All other metals can have more than one oxidation state.

    c) Examples:
    Iron(III)* oxide, Fe2O3 (given in the name Fe+3, and rule 7 O-2. Total charge (rule 2): (+3)x2 + (-2)x3 = 0
    Iron(II)* oxide, FeO (given in the name Fe+2, and rule 7 O-2 Total charge (rule 2): (+2)x1 + (-2)x1 = 0
    *Iron can be either +2 or+3, so the charge must be indicated in the name with Roman numerals.

    B) Nomenclature for Polyatomic Ions

    1 . Polyatomic cations (cations are positive ions). There are only two you need to know:
    ammonium, \(NH_4^+\) , and mercury (I), \(Hg_2^{+2}\)
    2 . Polyatomic anions (anions are negative ions):

    Here is a system that can help you memorize some of the polyatomic anions.

    • First memorize the -ate ions (shaded) in the first table (on the next page) and all the ions in the second table.
    • Second, memorize the rules below for naming the polyatomic ions that are related to the -ate ions.

    Here are the rules for naming other ions if you know the -ate ions.

    1. If you remove one oxygen from the -ate anion, you have an -ite anion. (e.g. bromate, \(BrO_3\), becomes bromite, \)BrO_2\)
    2. If you remove one oxygen from the -ite anion, you have an hypo- -ite anion. (e.g. bromite, \(BrO_2\), becomes hypobromite, \(BrO^-\))
    3. If you add one oxygen to the -ate anion, you have a per- -ate anion. (e.g. bromate, \(BrO_3^-\), becomes perbromate, \(BrO_4\)

    Here is the system for naming the corresponding acids if you know the -ate ions and the rules above.
    a) The -ate ion makes an -ic acid when enough H+ 's are added to make the molecule neutral.
    (e.g. bromate BrO3-, becomes Bromic acid, HBrO3) (Don't forget H is plus one)
    b) The -ite ion makes an -ous acid when enough H+ 's are added to make the molecule neutral.
    (e.g. bromi te, BrO2-, becomes Bromous acid, HBrO2)
    c) The hypo -ite ion makes a hypo -ous acid when enough H+ 's are added to make the molecule neutral.
    (e.g. hypobromite BrO-, becomes hypobromous acid, HBrO)
    d) The per -ate ion makes a per -ic acid when enough H+ 's are added to make the molecule neutral.
    (e.g. perbromate BrO4 -, becomes perbromic acid, HBrO4 )
    e) The -ide ion (no oxygens) makes a hydro -ic acid when enough H+ 's are added to make the molecule neutral.
    (e.g. Bromide Br-, becomes hydrobromic acid, HBr(aq)). (However, the gas, HBr(g)is called hydrogen bromide;
    (aq)means in water, that is,aqueous, and (g) means gas phase.)

    -ate ions (must be memorized)

    Also the -ic acids and -ite anions are shown to help show some of the rules from the last page.
    -ate Anion Chemical -ic Acid Chemical -ite Anion Chemical Mnemonic
    Name Formula Name Formula Name Formula
    sulfate SO4
    -2 sulfuric acid H2SO4 Sulfite SO3
    -2 (Super
    phosphate PO4
    -3 phosphoric acid H3PO4 phosphite PO3
    -3 Popeye
    carbonate CO3-2 carbonic acid H2CO3 skip skip Constantly
    chlorate ClO3
    - chloric acid HClO3 chlorite ClO2
    - Clubbed
    bromate BrO3
    - bromic acid HBrO3 bromite BrO2
    - Brutus
    iodate IO3
    - Iodic acid HIO3 iodite IO2
    - In
    nitrate NO3
    - nitric acid HNO3 nitrite NO2
    - Nevada)

    Below are more polyatomic anions whose names must be memorized:

    Name Formula Name Formula

    • hydroxide OH- thiosulfate S2O3-2 (thio tells you that one of the oxygens on a sulfate has been replaced by a sulfur)
    • cyanide CN- hydrogen sulfate *HSO4 - (or"bisulfate")
    • oxalate C2O4-2 hydrogen carbonate *HCO3 - (or "bicarbonate")
    • permanganate MnO4-
    • chromate CrO4-2
    • acetate C2H3O2- or C2H3OO- or CH3COOdichromate Cr2O7-2

    *Note: These are not named as acids because they are charged species.

    C) Nomenclature for compounds with Polyatomic ions

    1. The net charge (the sum of all the charges) in the compound must equal zero (rule 2). The name of the polyatomic ion is used. The metal is named first and if the metal has more than one common charge, the charge must be given as part of the name.

    2. Examples:
    lithium nitrate, LiNO3 (rule 3 for Li+, NO3
    - so, (+1) + (-1) = 0)
    calcium nitrate, Ca(NO3)2 (rule 5 for Ca+2, NO3
    - so, (+2) + (-1)x2 = 0)
    iron(II) phosphate, Fe3(PO4)2 (given in name Fe+2, PO4
    -3 so, (+2)x3 + (-3)x2 = 0)
    iron(III) phosphate, FePO4 (given in name Fe+3, PO4
    -3 so (+3)x1 + (-3)x1 = 0)
    magnesium sulfate, MgSO4 (rule 5 Mg+2; we have memorized that sulfate is -2.)
    gold(I) sulfate, Au2SO4 (sulfate is always -2 To find Au charge: (+X)x2 + (-2) = 0, so X = +1)
    copper(II) nitrite, Cu(NO2)2 (nitrite is always -1; (+X)x1 + (-1)x2 = 0 so X = +2)
    hypoiodous acid, HIO(aq) (IO3- is iodate, so IO - is hypoiodite)
    hydroiodic acid, HI (I- is iodide)
    chromic acid, H2CrO4 (CrO4-2 is chromate)
    Oxyacids, Their Anions, and Nomenclature

    Actually, you need to learn the acid names and the per-ate, -ate, -ite, and hypo-ite anions referred to in the preceding (page 2). The tables below summarize many of the rules.

    In the cases presented here, an acid is a compound that can donate hydrogens in water. Oxyacids are acids that contain oxygen in the anion (negative) species.

    Memorize all the -ic acids and their corresponding -ate anions in Table 1 below. Also learn the ionization equations for the acids and note that the negative charge of the anion is equal to the number of positive hydrogens that dissociate1 from the acid.

    Table 1 Total Ionization Equations of Selected Acids

    Acid Name (-ic acids) Total Ionization Equation of Acid Anion Name (-ate anions)
    chloric acid, HClO3 (aq)2 HClO3 (1) (in H2O) ====> H+(aq) + ClO3- (aq) chlorate: ClO3-
    nitric acid, HNO3 (aq) HNO3 (l) (in H2O) ====> H+(aq) + NO3- (aq) nitrate: NO3-
    sulfuric acid, H2SO4 (aq) H2SO4 (l) (in H2O) ====> 2H+(aq) + SO4-2 (aq) sulfate: SO4-2
    carbonic acid1, H2CO3 (aq) H2CO3 (s) (in H2O) ====> 2H+(aq) + CO3-2 (aq) carbonate: CO3-2
    phosphoric acid1, H3PO4(aq) H3PO4 (s) (in H2O) ====> 3H+(aq) + PO4-3 (aq) phosphate: PO4-3
    hydrochloric acid3, HCl (aq) HCl (g) (bubbled into H2O) ====>H+(aq) + Cl-(aq) chloride: Cl-

    1 Carbonic and phosphoric acids do not totally dissociate in water, but pretend they do to learn the nomenclature.

    The anions of these oxyacids often occur in other compounds.

    2 All oxyacids from the halogens, F, Cl, Br, and I follow the same nomenclature rules. Also note: (aq) stands for aqueous; it means the ionic species is dissolved in water. The (s) means solid, (l) means liquid, and (g) means gas.

    3 The chloride ion in hydrochloric acid is not polyatomic but is included for comparison. Also note that HCl(aq), is called hydrochloric acid if it is an aqueous solution, but it is called hydrogen chloride, HCl(g), if it is a pure gas. Similarly, HBr(aq) is called hydrobromic acid, but HBr(l) is called hydrogen bromide.

    Once you have learned the -ic acids and -ate anions from Table 1, you may substitute them into the row in Table 2 which is shaded and says Same. By learning the different prefixes and suffixes for acids and anions with more or fewer oxygens than the memorized Same species, you can predict the proper name for many related oxyacids and their corresponding anions.

    Table 2 Prefixes and Suffixes in Acid and Anion Nomenclature
    Oxygen Atoms Compared
    to the memorized -ic Acids
    and -ate Anions (above chart)
    Acid Prefix and/or Suffix
    (Example: name; formula)
    Anion Prefix and/or Suffix
    (Example: name; formula)
    One more oxygen than Same
    (the Same as learned in top chart)
    (perchloric; HClO4)
    (perchlorate; ClO4-)
    the Same -ic acid & -ate anion
    (the Same as learned in top chart)
    (chloric; HClO3)
    (chlorate; ClO3-)
    One less oxygen than Same -ous
    (chlorous; HClO2)
    (chlorite; ClO2-)
    Two less oxygens than Same hypo-ous
    (hypochlorous; HClO or HOCl)
    (hypochlorite; ClO- or OCl-)
    No oxygens hydro-ic
    (hydrochloric; HCl)
    (chloride; Cl-)
    D) See how you can do! (answers are given at the end)
    1 . Give the ox. st. for each element in each of the following (may not be needed to name these):
    a) NO ox. st. Nitrogen__________ ox. st. Oxygen__________
    b) N2O ox. st. Nitrogen__________ ox. st. Oxygen__________
    c) ClO4
    - ox. st. Chlorine__________ ox. st. Oxygen__________
    d) K2O2 ox. st. Potassium___________ ox. st. Oxygen__________
    e) Fe2O3 ox. st. Iron__________ ox. st. Oxygen__________
    f) SF6 ox. st. Sulfur__________ ox. st. Fluorine__________
    g) SO4
    -2 ox. st. Sulfur__________ ox. st. Oxygen__________
    h) SO3
    -2 ox. st. Sulfur__________ ox. st. Oxygen__________
    i) CaBr2 ox. st. Calcium__________ ox. st. Bromine__________
    j) FeO ox. st. Iron__________ ox. st. Oxygen__________
    2 . Give the correct chemical formula for each of the following:
    a) barium chloride _________________ g) iron(II) phosphate _________________
    b) sulfur dioxide _________________ h) gold(I) thiosulfate _________________
    c) disulfur tetroxide _________________ i) cobalt(III) cyanide _________________
    d) iron(II) bromide _________________ j) aluminium nitrite _________________
    e) calcium nitrate _________________ k) sulfur hexachloride _________________
    f) hydrosulfuric acid _________________ l) nitrous acid _________________
    3 . Give the correct name for each of the following:
    a) S2O3 ______________________ g) AgNO ______________________
    b) SrO ______________________ h) Co2(S2O3)3 ______________________
    c) Fe2(SO3)3 ______________________ i) Al(OH)3 ______________________
    d) SBr2 ______________________ j) K2CrO4 ______________________
    e) CoO ______________________ k) Sn3(PO4)2 ______________________
    f) H2CO3(aq) ______________________ l) HNO(aq) ______________________
    1) a.+2,-2 b.+1,-2 c.+7,-2 d. +1,-1 (yes, this is correct use rules) e. +3, -2 f. +6, -1 g. +6, -2 h.+4, -2 i.+2, -1 j.+2, -2
    2) a. BaCl2 b. SO2 c. S2O4 d. FeBr2 e. Ca(NO3)2 f. H2S(aq) g. Fe3(PO4)2 h. Au2S2O3 i. Co(CN)3 j. Al(NO2)3
    k. SCl6 l. HNO2(aq)
    3) a. disulfur trioxide b. strontium oxide c. iron(III) sulfite d. sulfur dibromide e. cobalt(II) oxide
    f. Carbonic acid g. silver hyponitrite h. cobalt(III) thiosulfate i. Aluminium hydroxide j. potassium chromate
    k. tin(II) phosphate l. hyponitrous acid


    • Rolf Unterleitner, SASC

    Chemical Nomenclature is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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