The chemical formula name converter above works in both directions. Give it a formula and it returns the systematic name, identifying whether the compound is ionic, covalent or an acid and applying the right set of rules to each. Give it a name and it returns the formula, working out the charges, crossing them over and reducing the result to its simplest whole-number ratio with brackets where they are needed. Every answer is converted back the other way as a check, and that check is displayed rather than hidden.
Arb Digital publishes free calculators for the steps that are mechanical but easy to get wrong under time pressure. Naming is exactly that: the rules are not difficult, but there are several sets of them, the set you need depends on what kind of compound you have, and the single commonest error is applying the covalent rules to an ionic compound or the reverse. The page decides which rules apply and says which it used, so the reasoning is visible.
What This Converter Does
In formula-to-name mode it parses the formula into a positive and a negative part, handling brackets and subscripts. For an ionic compound it names the cation, works out its charge from the charge balance, adds a Roman numeral where the metal has more than one common charge, and names the anion. For a covalent compound it applies Greek prefixes to both elements and elides the vowel where convention requires it, so it produces dinitrogen pentoxide rather than dinitrogen pentaoxide. For a compound that is an acid in aqueous solution it applies the acid naming rules.
In name-to-formula mode it runs the same logic backwards. It identifies the cation and anion from their names, reads any Roman numeral, takes the two charges and crosses them over, divides by their greatest common divisor and adds brackets around a polyatomic ion that appears more than once. Magnesium oxide comes out as MgO rather than Mg2O2, because the reduction step is part of the rule rather than an optional tidy-up.
The boundary against the adjacent tool is worth stating. The molar mass calculator also parses a formula, brackets and hydrates included, but it does so to compute a mass in grams per mole. It does not name anything. This page names it and does not weigh it. The two are natural neighbours: identify the compound here, then take the formula there for the mass.
How to Use It
- Choose a direction and type into the box. The hint text and the labels change to match.
- Mind the capitalisation of symbols. Element symbols have a capital first letter and a lower-case second, so CO is carbon monoxide and Co is cobalt. This is the single most common input error.
- Write brackets normally. Al2(SO4)3 and Fe(NO3)3 parse as written; the subscript after a bracket applies to the whole group.
- Give the Roman numeral when naming to a formula, as in iron(III) chloride. Without it the charge on a variable metal is not determined.
- Read the round-trip box. It converts the answer back the other way, which catches a mistyped subscript immediately.
How the Conversion Works
Parsing a formula begins by peeling off the leading group, which is either a bracketed polyatomic ion with a subscript or the longest element symbol that matches a known cation. Whatever remains is the anion, and it is looked up whole first, so SO4 is recognised as sulfate rather than being read as a sulfur atom followed by four oxygens. Only if the whole remainder is not a known ion is a trailing subscript stripped and the lookup retried, which is how Cl2 in CaCl2 resolves to two chloride ions.
The charge on the metal then comes from the charge balance rather than from a table. Working the default, Fe2(SO4)3 has three sulfate ions, each carrying two negative charges, so the anion side totals six. Two iron atoms must supply six positive charges between them, so each is three, and the compound is iron(III) sulfate. The same reasoning gives copper(II) in CuSO4 and tin(IV) in SnO2, and it is why a formula alone is enough to determine an oxidation state that no table lookup could supply.
Going the other way, the two charges are crossed over: a metal charge of three and an anion charge of two give three anions and two cations, which is where the subscripts in Fe2(SO4)3 come from. The result is then divided by the greatest common divisor of the two counts, so calcium at two and oxide at two reduces to CaO rather than staying as Ca2O2. Brackets are added around any polyatomic ion whose count exceeds one. The conventions underlying all of this are maintained by IUPAC, the recognised authority on chemical nomenclature.
Roman Numerals: Which Metals Need Them
A Roman numeral in a name gives the charge on the metal ion, and it is required whenever that charge is not fixed by the element. Sodium is always plus one and calcium always plus two, so writing sodium(I) chloride is not wrong so much as redundant. Iron can be plus two or plus three, and iron chloride is genuinely ambiguous: it could be FeCl2 or FeCl3, which are different substances with different colours and different chemistry.
The metals that need a numeral are broadly the transition metals plus the heavier p-block metals: iron, copper, chromium, manganese, cobalt, nickel, tin, lead, mercury, gold, platinum, titanium and vanadium among the common ones. Zinc, silver, cadmium and aluminium are transition or post-transition metals with effectively one common charge each, so they are conventionally written without a numeral. Group 1 and group 2 metals never take one.
An older naming system is still encountered and is worth recognising even though this page does not produce it. It used the suffixes -ous and -ic on a Latin stem for the lower and higher of two charges, giving ferrous for iron(II) and ferric for iron(III), cuprous for copper(I) and cupric for copper(II), stannous and stannic for tin. The system cannot express a metal with three or more common charges, which is why it was superseded, but it survives in older literature, in some industrial usage and in a few common names.
Ionic and Covalent Compounds Follow Different Rules
Greek prefixes appear in covalent names and not in ionic ones, and mixing the two systems produces names that are recognisably wrong to anyone reading them. Calcium chloride is not calcium dichloride, even though the formula is CaCl2, because the subscripts in an ionic formula are determined entirely by the charges and carry no independent information. Once you know the compound is calcium and chloride, the formula follows, so a prefix would be redundant.
Covalent compounds are the opposite case. Nitrogen and oxygen form NO, NO2, N2O, N2O3, N2O4 and N2O5, all of which exist and none of which is determined by any charge rule. The prefixes are load-bearing: without them the name does not identify the compound. This is why the mono- prefix is dropped from the first element but kept on the second where it is needed, giving carbon monoxide rather than monocarbon monoxide, and carbon dioxide rather than carbon dioxide with a leading prefix.
The vowel elision is a small point that catches people writing names by hand. Where a prefix ending in a or o meets an element name beginning with a vowel, the prefix loses its final letter: monoxide rather than monooxide, pentoxide rather than pentaoxide, tetroxide rather than tetraoxide, decoxide rather than decaoxide. Prefixes ending in i keep it, so dioxide and trioxide are correct as they stand. The converter applies this automatically.
The -ide, -ate and -ite Endings
Three endings carry most of the information in an anion name. An -ide ending on a single element means the simple anion: chloride, oxide, sulfide, nitride. It is also used for a small number of polyatomic ions that behave like simple ones, notably hydroxide and cyanide, which is a genuine irregularity rather than a pattern.
The -ate and -ite endings distinguish members of an oxyanion family. Within a family, -ate is the one with more oxygen and -ite the one with less: sulfate is SO4 and sulfite SO3, nitrate is NO3 and nitrite NO2, phosphate is PO4 and phosphite PO3. Crucially the endings are relative rather than absolute. Sulfate carries four oxygens and nitrate three, so you cannot infer the oxygen count from the ending alone; you can only infer which of a pair has more.
The halogens extend the pattern to four members using two additional affixes. For chlorine the series runs hypochlorite with one oxygen, chlorite with two, chlorate with three and perchlorate with four. The per- prefix means one more oxygen than the -ate form, and hypo- means one fewer than the -ite form. The same four-member pattern applies to bromine and iodine.
Acids are named from the anion they contain. An -ate anion gives an -ic acid, so sulfate gives sulfuric and nitrate gives nitric. An -ite anion gives an -ous acid, so nitrite gives nitrous and sulfite sulfurous. A simple -ide anion gives a hydro- prefix with an -ic ending, so chloride gives hydrochloric. The converter reports the acid name where the formula begins with hydrogen and the remainder is a recognised anion.
What This Converter Cannot Do
The scope is deliberately limited to compounds where a name follows mechanically from a formula. Organic nomenclature is out of scope entirely, and for good reason: the name of an organic compound depends on connectivity, not composition. C2H6O could be ethanol or dimethyl ether, and no amount of parsing a molecular formula distinguishes them, because the difference lies in which atom is bonded to which. Naming those requires a structure, and a structure is not what a molecular formula contains. If you are working from measured composition rather than a known formula, the empirical formula calculator and the percent composition calculator are the tools for that stage.
Coordination compounds are also excluded. Their names use ligand prefixes, a defined ligand ordering and an oxidation state in brackets, and the formula conventions differ from those of a simple salt. Hydrates are named with a Greek prefix and the word hydrate appended, which is a straightforward extension but one that depends on the dot notation being present in the input.
The ion tables cover the common cations and the standard polyatomic anions rather than every ion that exists, so an unusual species will return a message saying it was not recognised rather than a guess. That is the intended behaviour: a naming tool that guesses is worse than one that declines, because a plausible wrong name is harder to catch than an obvious blank. Where a name or formula needs checking against measured data for a real substance, the NIST Chemistry WebBook indexes compounds by both name and formula.
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Browse All Free Tools Suggest a ToolCommon Mistakes to Avoid
- Mis-capitalising a symbol — CO is carbon monoxide and Co is cobalt, and the two parse to entirely different compounds.
- Using Greek prefixes on an ionic compound — calcium chloride, never calcium dichloride, because the charges already fix the subscripts.
- Omitting a Roman numeral on a variable metal — iron chloride does not identify a compound, since FeCl2 and FeCl3 both exist.
- Forgetting to reduce the crossed charges — calcium and oxide both carry two, so the formula is CaO and not Ca2O2.
- Reading -ate as a fixed number of oxygens — the ending only says which member of a family has more oxygen, and sulfate has four while nitrate has three.
Related Free Tools From Arb Digital
Take the formula this page produces to the molar mass calculator for grams per mole, or to the percent composition calculator for the mass breakdown. The chemical equation balancer and the net ionic equation calculator take it into a reaction, the molarity calculator takes it into solution, and the empirical formula calculator is where to start if you are working back from measured composition. For the atomic side, see the electron configuration calculator and the average atomic mass calculator. The full free online tools hub lists everything else.
Frequently Asked Questions
Whenever the metal has more than one common charge, which covers most transition metals and the heavier p-block metals. Group 1 and group 2 metals, along with zinc, silver, cadmium and aluminium, have a fixed charge and take no numeral.
Because it is ionic, and in an ionic compound the subscripts are fixed by the charges. Once you know the ions are calcium and chloride the formula follows, so a prefix would add nothing. Greek prefixes belong to covalent naming.
Sulfate has four oxygens and sulfite three. The -ate ending marks the member of an oxyanion family with more oxygen and -ite the one with less, but the endings are relative, so they do not give an absolute count.
Because a Greek prefix ending in a or o loses that letter when the element name begins with a vowel. The same rule gives monoxide, tetroxide and decoxide, while prefixes ending in i keep it, as in dioxide and trioxide.
No. An organic name depends on how the atoms are connected, not on the molecular formula, and C2H6O could be ethanol or dimethyl ether. Naming those requires a structure rather than a composition.
An -ate anion gives an -ic acid, so sulfate gives sulfuric. An -ite anion gives an -ous acid, so nitrite gives nitrous. A simple -ide anion takes a hydro- prefix with an -ic ending, giving hydrochloric from chloride.
They are the older names for iron(II) and iron(III), from a system that used -ous for the lower charge and -ic for the higher on a Latin stem. It cannot express a metal with three or more charges, which is why Roman numerals replaced it.
This converter is provided for education and general reference. It applies standard naming conventions to common ionic, covalent and acid compounds, and is not a substitute for an authoritative chemical registry when identifying a real substance.
