oxidation numbers -...

OXIDATION NUMBER (#)

In ionic compounds, ox # of an ion = the charge of the ion, eg, +2 for Ca+2 and -2 for O-2 in CaO.In polar compounds, ox # of an atom = the charge it would have if it were an ion (if all electrons in each bond are assigned to the more electronegative* atom), eg, +2 for C and -2 for O in CO.In elements and pure covalent compounds, ox # of all atoms = zero, eg, H2, N2, O2, F2, Cl2, Br2, I2, P4, S8, PH3

In ionic and polar compounds most atoms can have more than one ox #. Memorize the few that have fixed ox #'s. They are:

+1 = Ag+, Group IA metals+2 = Cd+2, Zn+2, and Group IIA metals +3 = most Group IIIA atoms (B+3, Al+3, Ga+3 & In+3)-1 = F-

Rules for Assigning Oxidation Numbers

1. Noble gases and atoms in elemental compounds have ox # = 0. eg. He, Cl2, O2, S8, etc.2. The sum of ox#'s of all atoms in a compound = 0 eg. NaCl: Na = +1, Cl = -1, [(+1) + (-1)] = 03. The sum of ox#'s of all atoms in a polyatomic ion = the charge on the polyatomic ion e.g. NH4

+

4. The ox # of a monatomic ion = its ionic charge, eg. ox # of Na+ = +1, of Ca+2 = +2, etc.5. In compounds containing unlike atoms:

A ‘-’ ox # is assigned to the more electronegative atomA ‘+’ ox # is assigned to the more electropositive atomeg. ICl EN (I) = 2.5 EN (Cl) = 3.0

ox # (I) = +1 ox # (Cl) = -16. The ox # of H is either +1 or -1

H is +1 when combined with more electronegative atoms as in H2O and HClH is -1 when combined with less electronegative atoms as in LiH, CaH2, and AlH3

7. The ox # of O is always -2 except in peroxides where it is always –1. Peroxides have one more oxygen than the normal oxide.

in hydrogen oxide (H2O), O = -2 but in hydrogen peroxide (H2O2), O = -1in sodium oxide (Na2O), O = -2 but in sodium peroxide (Na2O2), O = -1

8. When a nonmetal is the more electronegative atom in a compound, its ox # equals the number of electrons needed to be isoelectronic with the nearest noble gas.

‘-’ ox # for Group IVA atoms = -4 in K4C C = -4‘-’ ox # for Group VA atoms = -3 in K3N N = -3‘-’ ox # for Group VIA atoms = -2 in K2O O = -2‘-’ ox # for Group VIIA atoms = -1 in KF F = -1

Nomenclature Review of 15

Note: In chemical formulas the less electronegative atom is usually written first and the more electronegative atom is usually written last, eg, H2O, BaBr2, AlF3, SO2, etc.Exceptions include NH3, CH4, and other organic compounds.

The more electronegative atom has the the highest ‘electronegativity’ as per Linus Pauling’s Table of Electronegativity. For example, F (EN=4.0) is more electronegative than C (EN=2.5).

OXIDATION NUMBER EXERCISEUsing the rules from the previous page, assign oxidation numbers to the underlined atoms in each compound.

1. Si F4

2. Cr I3

3. C O2

4. Mn O4-

5. CaC2

6. S O3-2

7. Br O3-

8. Sn Br4

9. Fe 2O3

10. Co 2S3

11. P 3O10-5

12. Mo 3P4

13. Sb 2O5

14. As 2O3

15. Os O4

16. Pt H4

17. BaO2

18. Cu 2C

19. Cr 2O7-2

20. W 3N5

21. H2SiF6

22. Na2B4O7

23. Cu 3N

24. HClO4

Answers:


1. +42. +33. +44. +75. –1 (an exception)6. +47. +58. +4

9. +310. +311. +512. +413. +514. +315. +816. +4

17. –1 (a peroxide)18. +219. +620. +521. +422. +323. +324. +7


RULES FOR NAMING INORGANIC COMPOUNDS ( The Stock System)

Naming Binary Compounds (compounds made of two different atoms):1. Think of compounds as having ‘+’ and ‘-’ atoms (even if they are not ionic).

The name of the more ‘+’ atom (the atom on the left side of the periodic table) is written first.If both atoms are in the same group, the atom which is lower in the table is more ‘+’.The name of the more ‘-’ atom is written last.

in NaCl sodium is more ‘+’ and chlorine is more ‘-’.

2. The name of the ‘+’ ion (cation) is the same as the element.in NaCl Na+ is called sodium (same as the element Na).

If the cation has more than one possible ox #, then state its ox # in Roman Numerals.FeCl2 is named iron(II) chloride FeCl3 is named iron(III) chlorideMnCl7 is manganese(VII) chloride TiCl4 is titanium(IV) chloride

3. To name the ‘-’ ion (anion), drop the ending of the element name and add the suffix "ide".SiC is silicon carbide AlP is aluminum phosphideCaO is calcium oxide KBr is potassium bromide

Formulas of Binary Compounds:1. Write the symbol of the ‘+’ ion (cation) first and the symbol of the ‘-’ ion (anion) last.Recall that the anion ends in "ide". 2. Using number subscripts, make the sum of the ox #'s in the compound = 0.It is often helpful to write the ox #'s of the ions before writing the formula of the compound.

name formula cation anioniron(II) iodide FeI2 Fe+2 I-

chromium(VI) oxide CrO3 Cr+6 O-2

zinc sulfide ZnS Zn+2 S-2

When combining ions with more complex ox #'s, use the inverse rule, i.e., use the ox # of the one symbol as the subscript for the other symbol.

Note that formulas such as Sn2O4 must be simplified to the lowest whole number subscripts.Try these.

arsenic(V) oxide As2O5 As+5 O-2

arsenic(III) oxide As2O3 As+3 O-2

aluminum sulfide Al2S3 Al+3 S-2

manganese(VII) sulfide Mn2S7 Mn+7 S-2

magnesium carbide Mg2C Mg+2 C-4

calcium nitride Ca3N2 Ca+2 N-3


THE PREFIX SYSTEM

For binary compounds containing 2 non-metals, a Greek or Latin prefix is attached to the name of an element to indicate the number of atoms of that element in the compound.

Number Prefix Formula Name

1 mono- CO carbon monoxide

2 di- SO2 sulfur dioxide

3 tri- SO3 sulfur trioxide

4 tetra- CCl4 carbon tetrachloride

5 penta- PCl5 phosphorus pentachloride

6 hexa- SF6 sulfur hexafluoride

7 = hepta, 8 = octa, 9 = ennea, 10 = deca, 11= hendeca, 12 = dodeca, 1/2 = hemi, 3/2 = sesquiNote: A prefix is attached to the 1st element only if more than 1 is present. Although this system is used almost exclusively for non-metal/non-metal compounds, occasionally, it is used when a metal is present.

Name the following using the Prefix system and the Stock System system.

Prefix System Name Stock System NameN2O dinitrogen monoxide nitrogen(I) oxideNO nitrogen monoxide nitrogen(II) oxideNO2 nitrogen dioxide nitrogen(IV) oxideN2O3 dinitrogen trioxide nitrogen(III) oxideN2O4 dinitrogen tetr(a)oxide nitrogen(IV) oxide (dimer)N2O5 dinitrogen pentoxide nitrogen(V) oxidePCl3 phosphorus trichloride phosphorus(III) chlorideP2O5 diphosphorus pentoxide phosphorus(V) oxideS2Cl2 disulfur dichloride sulfur(I) choride (dimer)As2O3 (di)arsenic trioxide arsenic(III) oxideAs2O5 diarsenic pentoxide arsenic(V) oxidePbO2 lead dioxide lead(IV) oxideMnO2 manganese dioxide manganese (IV) oxideU3O8 triuranium octaoxide uranium(5 1/3) oxide (not used)Fe3O4 triiron tetr(a)oxide iron(2 2/3) oxide (not used)

common names include: black iron oxide or magnetite ore or magnetic iron ore

Note: In the stock system, there is no space between the cation name and the oxidation number.


THE “ous-ic” SYSTEM

For binary compounds in which the cation has only 2 valences, the old “ous-ic” system is sometimes used. Use the Latin name of the first element and add the suffix “ous” for the lower valency and use “ic” for the higher valency.

Symbol Name Latin Name

Cu copper cuprum

Fe iron ferrum

Pb lead plumbum

Sn tin stannum

Au gold aurum

Name the following compounds using the “ous-ic” system.

ous-ic Name Stock System Name

PbCl2 plumbous chloride lead(II) chloride

PbCl4 plumbic chloride lead(IV) chloride

SnBr2 stannous bromide tin(II) bromide

SnBr4 stannic bromide tin(IV) bromide

Cu2O cuprous oxide copper(I) oxide

CuO cupric oxide copper(II) oxide

FeO ferrous oxide iron(II) oxide

Fe2O3 ferric oxide iron(III) oxide

Hg2O mercurous oxide mercury(I) oxide

HgO mercuric oxide mercury(II) oxide

PtCl2 platinous chloride plantinum(II) chloride

PtCl4 platinic chloride platinum(IV) chloride

CoO cobaltous oxide cobalt(II) oxide

Co2O3 cobaltic oxide cobalt(III) oxide

Ce2(SO4)3 cerous sulfate cerium(III) sulfate

Ce(SO4)2 ceric sulfate cerium(IV) sulfate


OXYACIDSOxyacids, like H2SO4 contain, in addition to a nonmetal, such as S, both hydrogen and oxygen. Students must memorize the names and formulas of the eight main oxyacids and their anions since many others are derived from these.

The Eight Main Oxyacids

Acid Name Acid Formula Polyatomic Anion Formula

Polyatomic Anion Name

1 acetic acid CH3COOH or HC2H3O2 CH3COO- or C2H3O2- acetate

2 chloric acid * HClO3 ClO3- chlorate

3 bromic acid * HBrO3 BrO3- bromate

4 iodic acid * HIO3 IO3- iodate

5 nitric acid HNO3 NO3- nitrate

6 carbonic acid H2CO3 CO3-2 carbonate

7 sulfuric acid H2SO4 SO4-2 sulfate

8 phosphoric acid H3PO4 PO4-3 phosphate

* Cl, Br and I are all in Group 7A of the periodic table and form analogous acids and polyatomic anions.

Many main oxyacids also exist in forms with more and/or less oxygens. For example, a sulfur oxyacid with one less oxygen than the main acid is sulfurous acid, H2SO3. A chlorine oxyacid with one more oxygen than the main acid is perchloric acid, HClO4. In the naming system of oxyacids, ‘per…ic’ means one more oxygen than the ‘ic’ acid, ‘ous’ means one less oxygen than the ‘ic’ acid and ‘hypo…ous’ means two less oxygens than the ‘ic’ acid.

A Car Never Stays Perfectly Clean

per …. ic * HClO4

…. ic HC2H3O2 H2CO3 HNO3 H2SO4 H3PO4 * HClO3

…. ous HNO2 H2SO3 H3PO3 * HClO2

hypo …. ous

H3PO2 * HClO

Note the patterns and learn the memory aid. * Cl may be replaced by Br or I.

Oxyacid anions and their salts are also named systematically. The anion of the ‘ ic’ acid ends with the suffix ‘ate’. ‘per…ate’ means the anion of the ‘per…ic’ acid, ‘ite’ means the anion of the ‘ous’ acid, and ‘hypo…ite’ means the anion of the ‘hypo…ous’ acid.

A Car Never Stays Perfectly Clean

per …. ate * ClO4-

…. ate C2H3O2- CO3

-2 NO3- SO4

-2 PO4-3 * ClO3

-

…. ite NO2- SO3

-2 ** HPO3-2 * ClO2

-

hypo …. ite ** H2PO2- * ClO-

* Cl may be replaced by Br or I. ** H3PO3 has only 2 acidic hydrogens so sodium phosphite is Na2HPO3

** H3PO2 has only 1 acidic hydrogen so sodium hypophosphite is NaH2PO2


SALTS OF OXYACIDS

Salts of oxyacids are named using the Stock System rules like binary compounds.

Formula Name Formula NameZn(C2H3O2)2

zinc acetate Sn(ClO3)2 tin(II) chlorate

Fe(C2H3O2)3 iron(III) acetate Pb(ClO2)4 lead(IV) chloriteCr(NO2)6 chromium(IV) nitrite Bi(ClO)5 bisthmus(V) hypochloriteMn(NO3)7 manganese(VII) nitrate HgBrO mercury(I) hypobromiteAl2(CO3)3 aluminum carbonate Co(BrO3)3 cobalt(III) bromateGa2(SO4)3 gallium sulfate Mo(BrO4)6 molybdenum(VI) perbromateK2SO3 potassium sulfite Sr(IO2)2 strontium ioditeBa3(PO4)2 barium phosphate NaIO4 sodium periodateCaHPO3 calcium phospite LiIO lithium hypoioditeMg(H2PO2)2 magnesium hypophosphite Be(IO3)2 beryllium iodateCd(ClO4)2 cadmium perchlorate Cu(BrO2)2 copper(II) bromite

BINARY ACIDS

Binary acids contain hydrogen and a non metal. They are all named as ‘hydro…ic’ acids when dissolved in water. In the anhydrous state (in parenthesis) they are named using standard notation.

HF = hydrofluoric acid (hydrogen fluoride)

HCl = hydrochloric acid (hydrogen chloride)

HBr = hydrobromic acid (hydrogen bromide)

HI = hydroiodic acid (hydrogen iodide)

H2S = hydrosulfuric acid (hydrogen sulfide)

HCN = hydrocyanic acid (hydrogen cyanide)


NAMING ACID(IC) SALTSPartially ionized polyprotic acids produce important polyatomic anions whose charges can be deduced from the original oxyacid and whose names must be memorized. The names may seem confusing at first because several conventions are used. It is important to remember that any chemical name must be unambiguous, i.e., it must be definitive, that is, each name can correspond to only one possible formula and the number of atoms must be clearly stated or must be readily determined from the name.

HCO3- (mono)hydrogen carbonate or bicarbonate

HSO4- (mono)hydrogen sulfate or bisulfate

HSO3- (mono)hydrogen sulfite or bisulfite

H2PO4-1 dihydrogen phosphate

H2PO3-1 dihydrogen phosphite

HPO4-2 monohydrogen phosphate

HPO3-2 monohydrogen phosphite

H2PO3-1 dihydrogen phosphite

H2PO3-2 dihydrogen hypophosphite

Note that the prefix “bi” means ‘half’ is only applicable to acid salts of diprotic acids. Since acid salts of diprotic acids can only have one hydrogen, the prefix “mono” is optional.In the case of acid salts of triprotic acids, “bi” cannot be used and further, the number of hydrogen’s remaining must be identified by the use of “mono” or “di”.

Keep in mind that in the foregoing, we are naming ions not compounds. These ions can and do form neutral compounds, called acid salts, by combining with metal cations and these are named as follows.

NaHSO4 sodium hydrogen sulfate or sodium bisulfateCa(HSO4)2 calcium hydrogen sulfate or calcium bisulfateAl(HSO4)3 aluminum hydrogen sulfate or aluminum bisulfate

NaH2PO4 sodium dihydrogen phosphate or monosodium phosphateor monosodium (di)hydrogen phosphate

Na2HPO4 sodium monohydrogen phosphate or disodium phosphateor disodium (mono)hydrogen phosphate

For compounds of monovalent cations like Na above, i.e., Li+, K+, etc., there are at least 3 acceptable names (as shown). For polyvalent cations, like Ca+2, Al+3, etc. the convention is to state the number of H’s but not the number of metal cations, as follows.

Ca(H2PO4)2 calcium dihydrogen phosphateCaHPO4 calcium monohydrogen phosphate

Al(H2PO4)3 aluminum dihydrogen phosphateAl2(HPO4)3 aluminum monohydrogen phosphate

Acid salts of sulfite are named like sulfate and acid salts of phosphite are named like phosphate.


Calculate the oxidation # of the underlined atom or groups of atoms in each compound.

1. N 2O

2. N 2O5

3. AlPO4

4. S O4-2

5. Cd(BrO2)2

6. Ga(ClO3)3

7. Si F4

8. Mg2SiO4

9. Na2CrO4

10. Cr O3

11. MnO2

12. Zn(HCO3) 2

13. K2CO3

14. NO2-1

15. SnO2

16. AgClO4

17. As2O5

18. P4O10

19. P2O7-4

20. TiBr3

Answers:1. +12. +53. +54. +65. +36. +57. +4

8. +49. +610. +6

11. +412. +413. +414. +315. +416. +717. +518. +519. +520. +3

Quiz Binary Compounds and Special Groups

Write the name of formula of the following compounds. Spelling counts.The column on the right will not be marked.

Formula Name Symbols & Oxid. #

Cs3PCu3N2

Mn2O7

PtCl2

SiH4

AlBHg3As2

Cd(CN)2

Zn(OH)2

Sb2O5

nickel(III) sulfideammonium phosphidechromium(III) oxide

molybdenum(V) silicidesilver cyanide

gold(III) bromidegallium carbideiron(III) sulfide

lead(IV) hydroxideberyllium nitride

Quiz Binary Compounds and Special Groups ANSWERS:



Cs3P cesium phosphide Cs+1(only) P-3(only)

Cu3N2 copper(II) nitride (Cu?)3 (N-3)2

Mn2O7 manganese(VII) oxide (Mn?)2 (O-2)7

PtCl2 platinum(II) chloride (Pt?) (Cl-1)2

SiH4 silicon hydride Si+4 (H-1)4

AlB aluminum boride Al+3(only) B-3

Hg3As2 mercury(II) arsenide (Hg?)3 (As-3)2

Cd(CN)2 cadmium cyanide Cd+2(only) [(CN)?]2

Zn(OH)2 zinc hydroxide Zn+2(only) [(OH)?]2

Sb2O5 antimony(V) oxide (Sb?)2 (O-2)5

Ni2S3 nickel(III) sulfide (Ni+3)? (S-2)?

(NH4)3P ammonium phosphide [(NH4)+1(only)]? (P-3)?

Cr2O3 chromium(III) oxide (Cr+3)? (O-2)?

Mo4Si5 molybdenum(V) silicide (Mo+5)? (Si-4)?

AgCN silver cyanide Ag+(only) CN-(only)

AuBr3 gold(III) bromide (Au+3)? (Br-1)?

Ga4C3 gallium carbide (Ga+3)? (C-4)?

Fe2S3 iron(III) sulfide (Fe+3)? (S-2)?

Pb(OH)4 lead(IV) hydroxide (Pb+4)? [(OH)-1]?

Be3N2 beryllium nitride [Be+2(only)]? [N-3]?

Oxyacids & Oxyacid Salts Name .........................................



(NH4)2SO3

chromium(III) sulfate

Ca(ClO)2

magnesium phosphate

barium acetate

Cu(BrO2)2

HBrO4

calcium iodite

mercury(II) hypobromite

lead(IV) chlorate

manganese(VII) carbonate

hydriodic acid

iodic acid

lithium peroxide

H2SO3

magnesium bicarbonate

LiHSO3

KHSO4

Na2HPO412H2O

gold(II) nitrite hexahydrate

HIO

HBrO2

HClO3

nitrous acid

sulfurous acid

calcium dihydrogen phosphate

aluminum monohydrogen phosphateOxyacids & Oxyacid Salts Answers



(NH4)2SO3 ammonium sulfite SO3-2 = sulfite

Cr2(SO4)3 chromium(III) sulfate (Cr+3)? (SO4-2)?

Ca(ClO)2 calcium hypochlorite OCl- = hypochlorite

Mg3(PO4)2 magnesium phosphate Mg+2(only), (PO4-3)only

Ba(CH3COO)2 barium acetate Ba+2, CH3COO- = acetate

Cu(BrO2)2 copper(II) bromite Cu+?, BrO2- = bromite

HBrO4 perbromic acid

Ca(IO2)2 calcium iodite Ca+2, IO2- = iodite

Hg(BrO)2 mercury(II) hypobromite Hg+2, BrO- = hypobromite

Pb(ClO3)4 lead(IV) chlorate Pb+4, ClO3- = chlorate

(Mn)2(CO3)7 manganese(VII) carbonate Mn+7, CO3-2 = carbonate

HI hydriodic acid

HIO3 iodic acid

Li2O2 lithium peroxide Li+1, O-1 = peroxide

H2SO3 sulfurous acid

Mg(HCO3)2 magnesium bicarbonate Mg+2, HCO3- = bicarbonate

LiHSO3 lithium bisulfite Li+1, HSO3- = bisulfite

KHSO4 potassium bisulfate K+, HSO4- = bisulfate

Na2HPO412H2O disodium phosphate dodecahydrate

Au(NO2)26H2O gold(II) nitrite hexahydrate Au+2, NO2-1 = nitrite

HIO hypoiodous acid

HBrO2 bromous acid

HClO3 chloric acid

HNO2 nitrous acid

H2SO3 sulfurous acid

Ca(H2PO4)2 calcium dihydrogen phosphate Ca+2, H2PO4-1 = diH phos.

Al2(HPO4)3 aluminum monohydrogen phosphate Al+3, HPO4-2 = monH phos.

oxidation numbers -...

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