Writing Formulas, Oxidation Numbers, and Nomenclature

Nomenclature of Covalent Compounds and Writing Formulas

Binary Molecular Compounds of Two Nonmetals (Covalent Compounds)

• Name the first element in the formula without modification, using its full name.
• Name the second element by modifying it to end with "-ide".
• Use prefixes to indicate the number of atoms of each element; never use "mono-" for the first element.

Subscript Prefixes

• 1 = mono- (not used on the first nonmetal)
• 2 = di-
• 3 = tri-
• 4 = tetra-
• 5 = penta-
• 6 = hexa-
• 7 = hepta-
• 8 = octa-
• 9 = nona-
• 10 = deca-

Nonmetal Naming

• Change the ending of the element name to "-ide".
  • IVA:
    • C = Carbide
    • Si = Silicide
  • VA:
    • N = Nitride
    • P = Phosphide
    • As = Arsenide
  • VIA:
    • O = Oxide
    • S = Sulfide
    • Se = Selenide
    • Te = Telluride
  • VIIA:
    • F = Fluoride
    • Cl = Chloride
    • Br = Bromide
    • I = Iodide
  • H = Hydride

Example: Naming Binary Covalent/Molecular Compounds, BF3

• Identify the major class: Boron (B) and Fluorine (F) are nonmetals, thus it's a covalent compound.
• Identify the subclass: Two elements indicate a binary covalent compound.
• Name the first element: Boron.
• Name the second element with an "-ide" ending: Fluorine becomes fluoride.
• Add prefixes: monoboron, trifluoride.
• Write the name, dropping "mono-" from the first element: Boron trifluoride.

Example: Naming Binary Covalent/Molecular Compounds, Cl2O7

• Identify the major class: Chlorine (Cl) and Oxygen (O) are nonmetals, thus it's a covalent compound.
• Identify the subclass: Two elements indicate a binary covalent compound.
• Name the first element: Chlorine.
• Name the second element with an "-ide" ending: Oxygen becomes oxide. Drop the last “a” from the prefix if the name begins with vowel.
• Add prefixes to indicate the subscript: dichlorine, heptoxide.
• Write the name: dichlorine heptoxide.

Practice Examples

• NO2: Nitrogen dioxide
• PCl5: Phosphorus pentachloride
• I2F7: Diiodine heptafluoride

Writing Formulas

• Sulfur hexachloride: $SCl_6$
• Tetraphosphorus nonasulfide: $P<em>4S</em>9$
• Disulfur trifluoride: $S<em>2F</em>3$

Predicting the Formula of Ionic Compounds

• Ionic compounds contain a metal and a nonmetal.
• Metals form cations (positive charge, lose electrons).
• Nonmetals form anions (negative charge, gain electrons).
• Ionic compounds are electrically neutral: the total positive charge must equal the total negative charge.

Writing the Formula of an Ionic Compound (e.g., Aluminum and Oxygen)

• Write the symbol for the metal cation and its charge: $Al^{+3}$.
• Write the symbol for the nonmetal anion and its charge: $O^{-2}$.
• Cross the charges (without signs) to become subscripts for the other ion: $Al<em>2O</em>3$.
• Reduce subscripts to the smallest whole-number ratio.
• Check that the total charge cancels: $Al = (2) \cdot (+3) = +6$, $O = (3) \cdot (-2) = -6$

Predicting Formulas with Polyatomic Ions

• Write the symbol for the cation and its charge.
• Write the symbol for the anion and its charge.
• Cross the charges to become subscripts.
• Reduce subscripts to the smallest whole-number ratio.
• Check that the total charge cancels.
• Example: $Cr^{+6}$ and $C<em>2O</em>4^{-2}$ becomes $Cr(C<em>2O</em>4)_3$.
  • $Cr = (2) \cdot (+6) = +12$
  • $C<em>2O</em>4 = (6) \cdot (-2) = -12$

Predicting Oxidation Numbers

• Oxidation number represents the number of electrons an element loses, gains, or shares in a bond.
  • Positive oxidation number: element loses or electrons are pulled away from an element.
  • Negative oxidation number: element gains or electrons are pulled toward an element.

Calculating Oxidation Numbers

• For Ions
  • The sum of the oxidation numbers equals the charge on the ion.
• For Neutral Species
  • The sum of all oxidation numbers equals zero.

Elements with Fixed Oxidation States

• +1: IA metals, H (when bonded to a non-metal), Ag
• +2: IIA metals, Zn, Cd
• +3: Al
• -1: F
• -2: O (except in peroxides $-1$ or superoxides $\rightarrow -\frac{1}{2}$)
• -1: Cl, Br, I (except when bonded to F or O)
• +1: H (when bonded to a non-metal)
  *Fixed Oxidation States:
  *IVA non-metals in binary ionic compounds.
  *VA non-metals in binary ionic compounds.
  *VIA non-metals in binary ionic compounds.

Calculating Oxidation Numbers for Neutral Species

• Example: K2CrO4
  • $2(+1) + 1(Cr) + 4(-2) = 0$
  • $Cr = +6$

Calculating Oxidation Numbers for Ions

• Example: $HCO_3^-$
  • $1(+1) + 1(C) + 3(-2) = -1$
  • $C = +4$

Practice

• IF7: I = +7 (F = -1)
• NaIO3: I = +5 (Na = +1, O = -2)
• K2Cr2O7: Cr = +6 (K = +1, O = -2)

Nomenclature (Naming Ionic Compounds/Salts)

• Ionic compounds are called salts, made of cations and anions.
• Name by simply naming the ions (cations and anions).

Cations

• Type I (fixed charge):
  • IA metals (+1), IIA metals (+2), Al (+3), Zn (+2), Ag (+1), Cd (+2)
• Type II (variable charge):
  • Transition metals, any metal not on the Type I list
    *Note: Only use Roman numerals in parenthesis for metals of variable charges. If the metal has a fixed charge, the Roman numeral is omitted from the name.

Anions

• Name the nonmetal, changing the ending to "-ide".
• Examples: Fluoride, Chloride, Oxide, Sulfide, Nitride

Common Polyatomic Ions

• +1: $NH_4^+$ (ammonium)
• +2: $Hg_2^{2+}$ (Mercury (I))
• -1: $OH^-$, $CN^-$, $SCN^-$, $MnO<em>4^-$, $C</em>2H<em>3O</em>2^-$
• -2: $CO<em>3^{2-}$, $CrO</em>4^{2-}$, $Cr<em>2O</em>7^{2-}$, $O<em>2^{2-}$, $C</em>2O_4^{2-}$

Patterns for Oxyanions

• Oxyanions contain oxygen and a nonmetal.
• Elements in the same column form similar oxyanions (same number of O's and same charge).
• Example: $ClO<em>3^-$ = chlorate, $BrO</em>3^-$ = bromate

More Polyatomic Ions (Oxyanions)

• -ate Groups (Examples):
  • $BO<em>3^{3-}$, $NO</em>3^{-}$, $SiO<em>3^{2-}$, $PO</em>4^{3-}$, $SO<em>4^{2-}$, $ClO</em>3^{-}$, $AsO<em>4^{3-}$, $SeO</em>4^{2-}$, $BrO<em>3^{-}$, $TeO</em>4^{2-}$, $IO<em>3^{-}$, $CO</em>3^{2-}$

Patterns in Oxyanions (-ate Group)

• +1 oxygen: "Per____ate"
• "Normal": "____ate"
• -1 oxygen: " ____ite"
• -2 oxygens: "hypo__ite"
  *Example:
  *BrO4 - Perbromate
  *BrO3 - bromate
  *BrO2 - bromite
  *BrO- hypobromite
• Charges do not change in the different forms, only the number of oxygens.

Example: Naming Binary Ionic, Type I Metal (Na2O)

• Identify major class: Na is a metal, O is a nonmetal, \ Ionic.
• Identify subclass: Two elements, \ Binary ionic.
• Metal Type: Na is in Group 1A, \ Type I.
• Identify ions: Cation = $Na^+$, Anion = $O^{2-}$
• Name ions: Sodium, Oxide
• Write name: Sodium oxide

Example: Naming Ionic with Polyatomic Ions, Type I Metal ($Ag<em>2CO</em>3$)

• Identify major class: Ag is a metal, O is a nonmetal, \ Ionic.
• Identify subclass: Ionic with polyatomic ions (ternary).
• Metal Type: Ag is Type I.
• Identify ions: Cation = $Ag^+$, Anion = $CO_3^{2-}$
• Name ions: Silver, Carbonate
• Write name: Silver carbonate

Practice

• KCl: Potassium chloride
• $MgBr_2$: Magnesium bromide
• $Al<em>2(SO</em>3)_3$: Aluminum sulfite

Naming Ionic Compounds with Metals that Form Multiple Cations

• Specify the charge of the metal cation using Roman numerals in parentheses.
• Example: Cu+ is Copper(I), Cu2+ is Copper(II)

Example: Naming Ionic, Type II Metal (CuCl)

• Identify major class: Cu is a metal, Cl is a nonmetal, \ Ionic.
• Identify subclass: Binary ionic.
• Metal Type: Cu is Type II.
• Identify ions: Cation = $Cu^+$, Anion = $Cl^-$
• Name ions: Copper(I), Chloride
• Write name: Copper(I) chloride

Example: Naming Ionic, Type II Metal ($Cu(NO<em>2)</em>2$)

• Identify major class: Cu is a metal, N and O are nonmetals, \ Ionic.
• Identify subclass: Ionic with polyatomic ions.
• Metal Type: Cu is Type II.
• Identify ions: Cation = $Cu^{+2}$, Anion = $NO_2^-$
• Name ions: Copper(II), Nitrite
• Write name: Copper(II) nitrite

Practice

• $Ti(ClO)_4$: Titanium(IV) hypochlorite
• $PbO_2$: Lead(IV) Oxide/ Plumbic Oxide
• $Fe<em>2S</em>3$: Iron(II) Sulfide/Ferrous Sulfide

Formulas from Ions

• Gold(I) tellurite: $Au<em>2TeO</em>3$
• Iron(III) bromide: $FeBr_3$

Exception (Mercury)

*Mercury (I): +1, exists as dimer $Hg<em>2^{2+}$ instead of Hg+ . *Mercury (II): Mercury +2 exists as $Hg^{2+}$ *Mercury (I) Chloride *cation: $Hg</em>2^{2+}$
*Anion: $Cl^-$
*Formula: $Hg<em>2Cl</em>2$
*Mercury (II) Chloride
*cation: $Hg^{2+}$
*Anion: $Cl^-$
*Formula: $HgCl_2$

Acids

• Acids are molecular compounds that behave as ionic compounds when dissolved in water.
• Form $H^+$ cation when dissolved in water and also a nonmetal anion.
• May be binary or oxyacid.
• (aq) indicates dissolved in water.
• Formula generally starts with H (except $H<em>2O$ and $H</em>2O_2$).

Nomenclature of Acids

• If the anion contains oxygen:
  • -ate \rightarrow -ic (root)ic acid
  • -ite \rightarrow -ous (root)ous acid
• If the anion does not contain oxygen:
  • hydro- + anion root + -ic \rightarrow hydro(anion root)ic acid

Example: Naming HCl

• Identify major class: First element is H, \ Acid.
• Identify subclass: Two elements, acid with no oxygen.

Example: Naming Binary Acids (HCl)

• Identify the anion: $Cl^-$ = chloride.
• Name the anion with an "-ic" suffix: chloride \rightarrow chloric.
• Add a "hydro-" prefix: hydrochloric.
• Add the word "acid": hydrochloric acid.

Acids without Oxygens

• HF (g): hydrogen fluoride, HF (aq): hydrofluoric acid
• HCl (g): hydrogen chloride, HCl (aq): hydrochloric acid
• HBr (g): hydrogen bromide, HBr (aq): hydrobromic acid
• HI (g): hydrogen iodide, HI (aq): hydroiodic acid
• $H<em>2S$ (g): hydrogen sulfide, $H</em>2S$ (aq): hydrosulfuric acid
• $H<em>2Se$ (g): hydrogen selenide, $H</em>2Se$ (aq): hydroselenic acid
• $NH<em>3$ (g): ammonia, $NH</em>3$ (aq) or $NH_4OH$: ammonium hydroxide (base)

Example: Naming H2SO4

• Identify major class: First element is H, \ Acid.
• Identify subclass: Oxyacid.

Example: Naming Oxyacids (H2SO4)

• Identify the anion: $SO_4^{2-}$ = sulfate.
• Change "-ate" to "-ic": sulfate \rightarrow sulfuric.
• Write the name: sulfuric acid.

Example: Naming Oxyacids (H2SO3)

• Identify major class: First element is H, \ Acid.
• Identify subclass: Oxyacid.

Example: Naming Oxyacids (H2SO3)

• Identify the anion: $SO_3^{2-}$ = sulfite.
• Change "-ite" to "-ous": sulfite \rightarrow sulfurous.
• Write the name: sulfurous acid.

Practice

• $H_2S$ (aq): hydrosulfuric acid
• $HClO_3$: chloric acid
• $HNO_2$: nitrous acid

Writing Formulas for Acids

• If the name ends in "acid", the formula starts with H.
• Write formulas as if ionic.
• "Hydro-" prefix means no oxygen.
• For oxyacids, "-ic" corresponds to "-ate", "-ous" corresponds to "-ite".

Example: Hydrosulfuric Acid

• $H^+$ with $S^{2-}$
• $H_2S$ (aq)

Example: Carbonic Acid

• $H^+$ with $CO_3^{2-}$
• $H<em>2CO</em>3$ (aq)

Example: Sulfurous Acid

• $H^+$ with $SO_3^{2-}$
• $H<em>2SO</em>3$ (aq)

Practice: Writing Formulas for Acids

• Chlorous acid: $HClO_2$
• Phosphoric acid: $H<em>3PO</em>4$
• Hydrobromic acid: HBr (aq)

Acids of Other Polyatomic Ions

• Hydrocyanic acid: HCN (aq)
• Hydrogen cyanide: HCN (g)
• Acetic acid: $HC<em>2H</em>3O_2$
• Oxalic acid: $H<em>2C</em>2O_4$

Naming Some Inorganic Compounds

• Acidic Salts: Made from ternary acids that retain one or more acidic hydrogen atoms.
• Modern system uses prefixes and the word "hydrogen."

Acid Anions

• Polyatomic ions with hydrogen (add "hydrogen-" prefix and add 1 to the charge).
• $CO<em>3^{2-}$ = carbonate \rightarrow $HCO</em>3^-$ = hydrogen carbonate
• $SO<em>3^{2-}$ = sulfite \rightarrow $HSO</em>3^-$ = hydrogen sulfite
• the addition of two hydrogens, the name adds dihydrogen- prefix
• $PO<em>4^{3-}$ = phosphate \rightarrow $H</em>2PO_4^{-1}$ = dihydrogen phosphate

Acid Salts

• Compounds derived from acid anions.
• Naming: Name the metal (Type I or II) followed by the name of the acid anion.

Example: $K<em>2HAsO</em>4$ Potassium hydrogen arsenate

Naming Some Inorganic Compounds

• $NaHCO_3$: sodium hydrogen carbonate
• $KHSO_4$: potassium hydrogen sulfate
• $KH<em>2PO</em>4$: potassium dihydrogen phosphate
• $K<em>2HPO</em>4$:

Hydrates

• Compounds that have water attached to them.
• Naming: Name the ionic salt followed by "____ hydrate", where ____ denotes the number of water molecules.
• $BaCl<em>2 \cdot 2H</em>2O$: Barium Chloride dihydrate.
  $CuSO<em>4 \cdot 5H</em>2O$: Copper (II) Sulfate pentahydrate