Chemical Name Calculator
Select a compound type, choose your ions or enter a formula, and get the correct IUPAC systematic name with a full worked explanation. The calculator handles binary ionic compounds, polyatomic-ion salts, variable-charge (Roman numeral) metals, binary covalent molecules with Greek prefixes, binary acids, oxoacids, and ionic hydrates. Each result shows the charge-balance steps so you can see exactly how the name is built.
How to name chemical compounds using IUPAC rules
Chemical nomenclature is the set of rules chemists use worldwide to give every compound a unique, unambiguous name. The system managed by the International Union of Pure and Applied Chemistry (IUPAC) covers four main families of inorganic compounds: ionic salts, covalent (molecular) compounds, acids, and hydrates. Each family follows its own naming rule, but the underlying goal is always the same: the name must encode exactly what atoms are present and, for ionic compounds, what charge each ion carries.
Naming ionic compounds: cations, anions, and Roman numerals
An ionic compound is named by placing the cation (positive ion) first, followed by the anion (negative ion). For monatomic anions, the element name is modified to end in -ide: chlorine becomes chloride, oxygen becomes oxide, sulfur becomes sulfide, and so on. Polyatomic anions keep their own systematic names (sulfate, nitrate, phosphate, carbonate, hydroxide, etc.) unchanged. When the metal cation can carry more than one charge, a Roman numeral is inserted in parentheses immediately after the metal name to specify the oxidation state: iron(II) for Fe2+ and iron(III) for Fe3+. Subscripts in the formula are determined by charge balance: the total positive charge must equal the total negative charge. For example, iron(III) and oxide (O2-) give Fe2O3 because two Fe3+ ions (+6 total) balance three O2- ions (-6 total).
Naming covalent compounds: Greek prefixes and the -ide rule
Covalent (molecular) compounds contain two nonmetals sharing electrons. IUPAC names them using Greek number prefixes to show exactly how many atoms of each element are present: mono (1), di (2), tri (3), tetra (4), penta (5), hexa (6), hepta (7), octa (8), nona (9), deca (10). The first element in the formula is named normally; "mono" is never placed before the first element. The second element takes the -ide suffix: SO3 is sulfur trioxide (not monosulfur trioxide), CO is carbon monoxide, N2O4 is dinitrogen tetroxide. If the prefix ends in a vowel and the element name also begins with a vowel, the prefix vowel is usually dropped for ease of pronunciation (e.g., pent + oxide = pentoxide, not pentaoxide).
Naming acids and hydrates
Binary acids contain hydrogen and one other nonmetal. In aqueous solution they are named with the prefix "hydro-", the stem of the nonmetal, and the suffix "-ic acid": HCl(aq) is hydrochloric acid, HBr(aq) is hydrobromic acid. Oxoacids contain hydrogen, oxygen, and another element. Their names come from the parent oxyanion: -ate anions yield -ic acids (sulfate gives sulfuric acid, nitrate gives nitric acid), and -ite anions yield -ous acids (sulfite gives sulfurous acid, nitrite gives nitrous acid). The prefixes "per-" and "hypo-" from the oxyanion carry over to the acid name unchanged. Hydrates are ionic compounds that trap water molecules in their crystal structure. The name is the anhydrous salt name followed by a Greek-prefix "-hydrate": CuSO4 . 5H2O is copper(II) sulfate pentahydrate. The number of water molecules per formula unit is shown in the formula with a centered dot.
IUPAC chemical nomenclature rules at a glance
| Compound type | Key rule | Example formula | Example name |
|---|---|---|---|
| Ionic - binary | Cation name + anion stem + -ide | NaCl | sodium chloride |
| Ionic - variable metal | Cation name + (Roman numeral) + anion name | FeCl3 | iron(III) chloride |
| Ionic - polyatomic anion | Cation name + polyatomic anion name (unchanged) | Na2SO4 | sodium sulfate |
| Covalent (molecular) | Greek prefix + element 1 + Greek prefix + element 2 -ide | SO3 | sulfur trioxide |
| Binary acid (aqueous) | hydro- + element stem + -ic acid | HBr (aq) | hydrobromic acid |
| Oxoacid | -ate anion -> -ic acid; -ite anion -> -ous acid | H2SO4 | sulfuric acid |
| Hydrate | Salt name + Greek prefix + -hydrate | CuSO4.5H2O | copper(II) sulfate pentahydrate |
Quick reference for the four main compound types covered by this calculator.
Frequently asked questions
When do I use a Roman numeral in a chemical name?
Roman numerals are used only for metals that can adopt more than one oxidation state - the so-called variable-charge or transition metals such as iron, copper, lead, tin, chromium, cobalt, manganese, gold, and mercury. A fixed-charge metal like sodium (always +1) or calcium (always +2) never needs a Roman numeral. The numeral tells you which charge that metal is carrying in this particular compound: FeCl2 is iron(II) chloride (Fe2+) and FeCl3 is iron(III) chloride (Fe3+).
What is the difference between an ionic and a covalent compound name?
Ionic compound names use the cation name followed by the anion name (with an -ide suffix for monatomic anions) and no Greek prefixes. Covalent compound names use Greek prefixes before both element names to show exact atom counts, and always end in -ide. The key indicator is the types of elements: a metal paired with a nonmetal almost always forms an ionic compound; two nonmetals bonded together form a covalent compound.
Why does "mono" never appear before the first element in a covalent name?
By IUPAC convention, the prefix "mono" is omitted from the first element in a binary covalent compound because it is redundant - there is no ambiguity about there being at least one atom of the first element listed. CO is carbon monoxide, not monocarbon monoxide. The second element always takes a prefix, including mono where appropriate (CO2 is carbon dioxide because "di" refers to the two oxygen atoms).
How do I find the subscripts in an ionic formula from the charges?
Use the crisscross rule: the numerical value of the cation charge becomes the subscript of the anion, and the numerical value of the anion charge becomes the subscript of the cation. Then reduce to the lowest whole-number ratio. For example, Al3+ and O2-: crisscross gives Al2O3. For Ca2+ and Cl-: crisscross gives Ca1Cl2, which simplifies to CaCl2.
What is a hydrate and how do you name one?
A hydrate is an ionic compound whose crystal structure includes a fixed number of water molecules per formula unit. Chemists write the number of water molecules after a centered dot: CuSO4 . 5H2O. The name is the anhydrous salt name followed by a Greek prefix and the word "-hydrate": copper(II) sulfate pentahydrate. Common hydrates include magnesium sulfate heptahydrate (Epsom salt, MgSO4 . 7H2O) and sodium carbonate decahydrate (washing soda, Na2CO3 . 10H2O).
What is the difference between a binary acid and an oxoacid name?
Binary acids (e.g., HCl, HBr, H2S) contain only hydrogen and one nonmetal. In aqueous solution they are named "hydro-[stem]-ic acid". Oxoacids (e.g., H2SO4, HNO3, H3PO4) also contain oxygen. Their names are derived from the parent polyatomic oxyanion: if the anion ends in -ate, the acid ends in -ic (sulfate gives sulfuric); if the anion ends in -ite, the acid ends in -ous (sulfite gives sulfurous).