Name That Compound
Free chemical nomenclature practice. See a formula and type its name, or flip it and write the formula, with instant grading and the rule behind every answer.
New to naming? Read the Chemical Nomenclature study guide → or grab the printable cheat sheet →
NaCl
How Chemical Nomenclature Works
Chemical nomenclature is the system for turning a compound’s formula into its name and back again. Which rule applies depends on the kind of compound, so this practice tool draws from five families:
- Binary ionic (Metal + nonmetal): A fixed-charge metal and a nonmetal. Name the metal, then the nonmetal root with -ide. No Greek prefixes.
- Multiple-charge metals (Stock (Roman numerals)): A metal with more than one common charge. Work out the charge from the anions, then show it as a Roman numeral in parentheses: iron(III).
- Polyatomic ions (Named ion groups): Compounds built from polyatomic ions (sulfate, nitrate, ammonium, hydroxide). Use the ion name unchanged; wrap it in parentheses when its subscript is > 1.
- Molecular (covalent) (Greek prefixes): Two nonmetals. Use Greek prefixes (mono-, di-, tri-, ...) to count each element. Drop mono- on the first element.
- Acids (hydro-/-ic/-ous): Aqueous acids. No oxygen → hydro-…-ic acid; from an -ate anion → -ic acid; from an -ite anion → -ous acid.
Every answer is graded the same way ChemWhiz’s Study engine grades it: your answer and the correct answer are each reduced to a canonical form and compared exactly. Chemical formulas are case-sensitive, because case is meaningful (Co is cobalt, CO is carbon monoxide), so element symbols must be capitalized correctly (NaCl, not nacl). Subscripts can be typed as ordinary digits (NaCl, Fe2(SO4)3); the grader reads a typed digit the same as a formatted subscript.
Naming trips up nearly every general-chemistry student, so drill one family at a time until it is automatic, then switch to “Write the formula” to practice the reverse direction. Use “Show answer” whenever you want the rule without guessing.
Frequently Asked Questions
How do you name an ionic compound?
Name the cation (metal or ammonium) first, then the anion. A monatomic anion takes an -ide ending (chloride, oxide, sulfide); a polyatomic ion keeps its own name (sulfate, nitrate, carbonate). Ionic names never use Greek prefixes, because the subscripts are fixed by charge balance, so calcium chloride is CaCl2, not "calcium dichloride".
When do you use Roman numerals in a chemical name?
Use a Roman numeral for metals that have more than one common charge, which is most transition metals plus tin and lead. Work out the metal’s charge from the anions, then show it in parentheses right after the metal name: FeCl3 is iron(III) chloride, FeCl2 is iron(II) chloride. Fixed-charge metals (Groups 1 and 2, aluminum, zinc) never take a Roman numeral.
What is the difference between naming ionic and molecular compounds?
Ionic compounds (a metal with a nonmetal or polyatomic ion) are named by charge balance and take no prefixes. Molecular compounds (two nonmetals) are named with Greek prefixes that count each atom: CO is carbon monoxide, CO2 is carbon dioxide, N2O4 is dinitrogen tetroxide. The prefix mono- is dropped on the first element.
How do you name acids?
An acid with no oxygen uses hydro-…-ic acid (HCl → hydrochloric acid). An oxoacid from an -ate anion becomes -ic acid (NO3- nitrate → HNO3 nitric acid); from an -ite anion it becomes -ous acid (NO2- nitrite → HNO2 nitrous acid).
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