Introduction: The Language of Chemistry
Chemical nomenclature is the systematic method of naming chemical compounds, providing a universal language that allows chemists worldwide to communicate precisely about chemical substances. Mastering chemical nomenclature is fundamental to success in chemistry, as it reveals crucial information about a compound’s composition, structure, and likely properties. This cheatsheet provides comprehensive guidelines for naming both ionic and covalent compounds according to IUPAC (International Union of Pure and Applied Chemistry) rules, with practical examples and troubleshooting tips for common naming challenges.
Core Principles of Chemical Nomenclature
Key Nomenclature Systems
- IUPAC system: International standard for systematic naming
- Common names: Traditional names still in use for many substances (e.g., water instead of dihydrogen monoxide)
- Stock system: Uses Roman numerals to indicate metal oxidation states
- Older systems: Including -ous/-ic suffixes for variable oxidation states
General Naming Process
- Identify compound type (ionic, molecular, acid)
- Apply specific rules for that category
- Write name with appropriate prefixes, suffixes, and numbers
Naming Ionic Compounds
Binary Ionic Compounds (Metal + Nonmetal)
| Component | Naming Rule | Examples |
|---|---|---|
| Metal cation (fixed charge) | Element name unchanged | Na⁺ = sodium |
| Metal cation (variable charge) | Element name + Roman numeral | Fe²⁺ = iron(II), Fe³⁺ = iron(III) |
| Nonmetal anion | Root + -ide suffix | Cl⁻ = chloride, O²⁻ = oxide |
General formula: Metal name + nonmetal root + -ide
Examples:
- NaCl: sodium chloride
- MgO: magnesium oxide
- FeCl₃: iron(III) chloride
- CuO: copper(II) oxide
Special cases:
- NH₄⁺ (ammonium) acts as a metal in nomenclature
- Hg₂²⁺ (mercury(I)) is diatomic mercury
Ionic Compounds with Polyatomic Ions
| Polyatomic Ion | Formula | Charge |
|---|---|---|
| Ammonium | NH₄⁺ | 1+ |
| Hydroxide | OH⁻ | 1- |
| Cyanide | CN⁻ | 1- |
| Nitrate | NO₃⁻ | 1- |
| Nitrite | NO₂⁻ | 1- |
| Acetate | CH₃COO⁻ | 1- |
| Carbonate | CO₃²⁻ | 2- |
| Sulfate | SO₄²⁻ | 2- |
| Sulfite | SO₃²⁻ | 2- |
| Phosphate | PO₄³⁻ | 3- |
General formula: Cation name + polyatomic ion name
Examples:
- NaOH: sodium hydroxide
- NH₄Cl: ammonium chloride
- Ca(NO₃)₂: calcium nitrate
- Fe₂(SO₄)₃: iron(III) sulfate
- Al(OH)₃: aluminum hydroxide
Hydrates
| Component | Naming Rule | Examples |
|---|---|---|
| Water molecules | Greek prefix + “hydrate” | monohydrate (1), dihydrate (2), etc. |
General formula: Ionic compound name + hyphen + prefix + hydrate
Examples:
- CuSO₄·5H₂O: copper(II) sulfate pentahydrate
- MgSO₄·7H₂O: magnesium sulfate heptahydrate
- CaSO₄·2H₂O: calcium sulfate dihydrate
Naming Covalent (Molecular) Compounds
Binary Molecular Compounds (Nonmetal + Nonmetal)
| Component | Naming Rule | Examples |
|---|---|---|
| First nonmetal | Name + Greek numerical prefix (except mono) | C = carbon, N = nitrogen |
| Second nonmetal | Greek prefix + root + -ide | Cl₂ = dichloride, O = monoxide |
General formula: Prefix + first element + prefix + second element root + -ide
Greek prefixes: 1 = mono (often omitted for first element) 2 = di 3 = tri 4 = tetra 5 = penta 6 = hexa 7 = hepta 8 = octa 9 = nona 10 = deca
Examples:
- CO₂: carbon dioxide
- N₂O: dinitrogen monoxide
- CCl₄: carbon tetrachloride
- P₄O₁₀: tetraphosphorus decaoxide
- SF₆: sulfur hexafluoride
Special cases:
- H₂O: water (common name used instead of dihydrogen monoxide)
- NH₃: ammonia (common name used)
Acids
Binary Acids (H + Nonmetal)
| Component | Naming Rule | Examples |
|---|---|---|
| Aqueous solution | “hydro” + nonmetal root + -ic acid | HCl(aq): hydrochloric acid |
General formula: hydro + nonmetal root + -ic acid
Examples:
- HCl(aq): hydrochloric acid
- HBr(aq): hydrobromic acid
- H₂S(aq): hydrosulfuric acid
Oxoacids (H + Polyatomic Ion with Oxygen)
| Polyatomic Ion | Naming Pattern | Example Acid |
|---|---|---|
| -ate ion | -ic acid | H₂SO₄: sulfuric acid |
| -ite ion | -ous acid | H₂SO₃: sulfurous acid |
| per- + -ate ion | per- + -ic acid | HClO₄: perchloric acid |
| hypo- + -ite ion | hypo- + -ous acid | HClO: hypochlorous acid |
Examples:
- HNO₃: nitric acid (from nitrate)
- HNO₂: nitrous acid (from nitrite)
- H₃PO₄: phosphoric acid (from phosphate)
- H₂CO₃: carbonic acid (from carbonate)
Organic Compounds (Basic Naming)
| Carbon Chain Length | Alkane | Alkene | Alkyne |
|---|---|---|---|
| 1 | methane | N/A | N/A |
| 2 | ethane | ethene | ethyne |
| 3 | propane | propene | propyne |
| 4 | butane | butene | butyne |
| 5 | pentane | pentene | pentyne |
| 6 | hexane | hexene | hexyne |
| 7 | heptane | heptene | heptyne |
| 8 | octane | octene | octyne |
| 9 | nonane | nonene | nonyne |
| 10 | decane | decene | decyne |
General pattern:
- Alkanes: -ane suffix (single bonds)
- Alkenes: -ene suffix (double bond)
- Alkynes: -yne suffix (triple bond)
Naming Compounds with Variable Oxidation States
Stock System (Current IUPAC)
| Element | Naming Pattern | Examples |
|---|---|---|
| Transition metals | Element + Roman numeral for oxidation state | Fe²⁺: iron(II), Fe³⁺: iron(III) |
General formula: Metal name + (oxidation number) + anion name
Examples:
- CuCl: copper(I) chloride
- CuCl₂: copper(II) chloride
- SnO: tin(II) oxide
- SnO₂: tin(IV) oxide
Classical System (Older Method)
| Oxidation State | Suffix | Examples |
|---|---|---|
| Lower | -ous | FeCl₂: ferrous chloride |
| Higher | -ic | FeCl₃: ferric chloride |
Examples in both systems:
- FeCl₂: iron(II) chloride (Stock) or ferrous chloride (classical)
- FeCl₃: iron(III) chloride (Stock) or ferric chloride (classical)
- CuO: copper(II) oxide (Stock) or cupric oxide (classical)
- Cu₂O: copper(I) oxide (Stock) or cuprous oxide (classical)
Determining Charges and Oxidation States
Common Ion Charges
Fixed-Charge Metals (Groups 1, 2, 13)
- Group 1 (alkali metals): Always 1+ (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Fr⁺)
- Group 2 (alkaline earth metals): Always 2+ (Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Ra²⁺)
- Group 13: Typically 3+ (Al³⁺, Ga³⁺)
Variable-Charge Metals (Transition Metals)
| Element | Common Oxidation States |
|---|---|
| Chromium | Cr²⁺, Cr³⁺, Cr⁶⁺ |
| Manganese | Mn²⁺, Mn⁴⁺, Mn⁷⁺ |
| Iron | Fe²⁺, Fe³⁺ |
| Cobalt | Co²⁺, Co³⁺ |
| Nickel | Ni²⁺, Ni³⁺ |
| Copper | Cu⁺, Cu²⁺ |
| Zinc | Zn²⁺ |
| Silver | Ag⁺ |
| Cadmium | Cd²⁺ |
| Tin | Sn²⁺, Sn⁴⁺ |
| Mercury | Hg₂²⁺, Hg²⁺ |
| Lead | Pb²⁺, Pb⁴⁺ |
Nonmetal Anions
- Group 17 (halogens): Always 1- (F⁻, Cl⁻, Br⁻, I⁻)
- Group 16: Typically 2- (O²⁻, S²⁻, Se²⁻)
- Group 15: Typically 3- (N³⁻, P³⁻)
Calculating Oxidation Numbers
- Free elements have oxidation number of 0
- Monatomic ions have oxidation number equal to their charge
- Oxygen usually has oxidation number of -2 (except in peroxides: -1)
- Hydrogen usually has oxidation number of +1 (except in metal hydrides: -1)
- Fluorine always has oxidation number of -1
- Sum of oxidation numbers equals total charge of the compound
Examples:
- In Fe₂O₃: 2(Fe) + 3(-2) = 0, so Fe = +3
- In Cr₂O₇²⁻: 2(Cr) + 7(-2) = -2, so Cr = +6
Common Prefixes and Suffixes
Prefixes
| Prefix | Meaning | Example |
|---|---|---|
| mono- | one | carbon monoxide (CO) |
| di- | two | carbon dioxide (CO₂) |
| tri- | three | sulfur trioxide (SO₃) |
| tetra- | four | carbon tetrachloride (CCl₄) |
| penta- | five | phosphorus pentachloride (PCl₅) |
| hexa- | six | sulfur hexafluoride (SF₆) |
| hepta- | seven | iodine heptafluoride (IF₇) |
| octa- | eight | osmium tetroxide (OsO₄) |
| nona- | nine | nonane (C₉H₂₀) |
| deca- | ten | decane (C₁₀H₂₂) |
| hypo- | below | hypochlorous acid (HClO) |
| per- | above | perchloric acid (HClO₄) |
Suffixes
| Suffix | Meaning | Example |
|---|---|---|
| -ide | simple anion | sodium chloride (NaCl) |
| -ate | oxoanion (more oxygen) | sodium sulfate (Na₂SO₄) |
| -ite | oxoanion (less oxygen) | sodium sulfite (Na₂SO₃) |
| -ic | higher oxidation state or oxoacid from -ate | ferric chloride (FeCl₃), sulfuric acid (H₂SO₄) |
| -ous | lower oxidation state or oxoacid from -ite | ferrous chloride (FeCl₂), sulfurous acid (H₂SO₃) |
Common Polyatomic Ions
Negative Ions (Anions)
| Name | Formula | Charge |
|---|---|---|
| Acetate | CH₃COO⁻ | 1- |
| Bicarbonate (hydrogen carbonate) | HCO₃⁻ | 1- |
| Bisulfate (hydrogen sulfate) | HSO₄⁻ | 1- |
| Carbonate | CO₃²⁻ | 2- |
| Chlorate | ClO₃⁻ | 1- |
| Chlorite | ClO₂⁻ | 1- |
| Cyanide | CN⁻ | 1- |
| Dichromate | Cr₂O₇²⁻ | 2- |
| Hydroxide | OH⁻ | 1- |
| Nitrate | NO₃⁻ | 1- |
| Nitrite | NO₂⁻ | 1- |
| Oxalate | C₂O₄²⁻ | 2- |
| Permanganate | MnO₄⁻ | 1- |
| Peroxide | O₂²⁻ | 2- |
| Phosphate | PO₄³⁻ | 3- |
| Sulfate | SO₄²⁻ | 2- |
| Sulfite | SO₃²⁻ | 2- |
| Thiocyanate | SCN⁻ | 1- |
Positive Ions (Cations)
| Name | Formula | Charge |
|---|---|---|
| Ammonium | NH₄⁺ | 1+ |
| Hydronium | H₃O⁺ | 1+ |
| Mercury(I) (mercurous) | Hg₂²⁺ | 2+ |
Common Compound Names and Formulas
Everyday Compounds
| Common Name | Chemical Name | Formula |
|---|---|---|
| Water | Dihydrogen monoxide | H₂O |
| Table salt | Sodium chloride | NaCl |
| Baking soda | Sodium bicarbonate | NaHCO₃ |
| Vinegar | Acetic acid (dilute) | CH₃COOH |
| Bleach | Sodium hypochlorite | NaClO |
| Lye | Sodium hydroxide | NaOH |
| Lime | Calcium oxide | CaO |
| Chalk | Calcium carbonate | CaCO₃ |
| Epsom salt | Magnesium sulfate heptahydrate | MgSO₄·7H₂O |
| Milk of magnesia | Magnesium hydroxide | Mg(OH)₂ |
| Hydrogen peroxide | Dihydrogen dioxide | H₂O₂ |
| Laughing gas | Dinitrogen monoxide | N₂O |
| Dry ice | Solid carbon dioxide | CO₂ |
Important Lab Compounds
| Chemical Name | Formula | Common Uses |
|---|---|---|
| Sodium hydroxide | NaOH | Base, cleaning agent |
| Hydrochloric acid | HCl | Acidifier, cleaning |
| Sulfuric acid | H₂SO₄ | Industrial chemical, batteries |
| Nitric acid | HNO₃ | Oxidizer, metal dissolution |
| Ammonium nitrate | NH₄NO₃ | Fertilizer |
| Silver nitrate | AgNO₃ | Halide test, photography |
| Potassium permanganate | KMnO₄ | Oxidizer, disinfectant |
| Copper(II) sulfate pentahydrate | CuSO₄·5H₂O | Fungicide, blue vitriol |
Naming Strategy Flowchart
Identify compound type:
- Contains metal + nonmetal? → Ionic compound
- Contains only nonmetals? → Molecular compound
- Contains hydrogen + anion in water? → Acid
For ionic compounds:
- Fixed-charge metal? → Metal name + nonmetal-ide
- Variable-charge metal? → Metal name(Roman numeral) + nonmetal-ide
- Contains polyatomic ion? → Name each ion
For molecular compounds:
- Binary compound? → Prefix-first element + prefix-second element-ide
- Contains oxygen + hydrogen? → Possibly an acid or base
For acids:
- Binary acid? → Hydro + nonmetal root + -ic acid
- Oxoacid? → Nonmetal root + -ic/-ous acid (per-/hypo- as needed)
Common Naming Challenges & Solutions
Challenge: Determining Oxidation State
Solution:
- Write the formula
- Assign known oxidation numbers
- Use algebra to find unknown
- Verify that total charge equals zero
Example: In Fe₃O₄
- Three iron atoms and four oxygen atoms
- Oxygen is -2
- 3(Fe) + 4(-2) = 0
- 3(Fe) = 8
- Fe has mixed oxidation state (Fe²⁺ and Fe³⁺)
Challenge: Naming Compounds with Multiple Polyatomic Ions
Solution:
- Name cation first
- Name anion second
- No multiplying prefixes needed
Example: Ca(NO₃)₂ = calcium nitrate (not calcium dinitrate)
Challenge: Determining if Prefixes are Needed
Solution:
- Ionic compounds: No prefixes (use oxidation numbers if needed)
- Molecular compounds: Always use prefixes to indicate number of atoms
Challenge: Acid Names vs. Anion Names
Solution:
- Memorize pattern: -ate → -ic acid; -ite → -ous acid
- Binary acids use hydro- prefix + -ic suffix
Resources for Further Learning
Recommended Books
- “Nomenclature of Inorganic Chemistry: IUPAC Recommendations 2005” (Red Book)
- “Nomenclature of Organic Chemistry: IUPAC Recommendations” (Blue Book)
- “Chemistry” by Zumdahl and Zumdahl
Online Resources
- IUPAC website (iupac.org)
- ChemSpider for compound lookups
- Khan Academy Chemistry
- Royal Society of Chemistry interactive periodic table
Practice Tools
- American Chemical Society naming practice
- ChemTeam nomenclature tutorials
- Interactive naming quizzes from the Royal Society of Chemistry
Mobile Apps
- IUPAC Nomenclature
- Chemical Formula Challenge
- Periodic Table (Royal Society of Chemistry)
This cheatsheet provides comprehensive guidance for naming chemical compounds following the IUPAC rules. Remember that practice is key to mastering chemical nomenclature, and the ability to name compounds correctly is essential for clear communication in chemistry. Regular exposure to chemical formulas and their names will help develop pattern recognition skills that make nomenclature increasingly intuitive over time.