Chemical names follow a small set of IUPAC rules. In an ionic compound the cation is named first and the anion second. A monatomic anion ends in “-ide” (chloride, oxide, nitride), polyatomic anions keep their own names (sulfate, nitrate, hydroxide), and a metal that can form more than one ion carries its charge as a Roman numeral – FeCl₂ is iron(II) chloride, FeCl₃ iron(III) chloride. The charge is found by making the formula neutral: three chloride ions (3 × −1) must be balanced by one Fe³⁺.
Compounds of two non-metals are molecular and use Greek prefixes instead: CO is carbon monoxide, N₂O₄ dinitrogen tetroxide, SF₆ sulfur hexafluoride. Acids are named from their anions – chloride gives hydrochloric acid, sulfate gives sulfuric acid, nitrite gives nitrous acid – and water of crystallisation becomes “pentahydrate” and so on.
Type a formula and the calculator works out which ions fit, checks the charges, applies the rules and explains each step. It also knows dozens of compounds whose names are not rule-based (water, ammonia, methane, glucose) and the everyday names of household chemicals. The second mode works like a table of ions: pick a cation and an anion to get the formula and name.
How to use the Chemical Name Calculator
- Mode
- Chemical formula — Examples: CuSO4·5H2O, (NH4)2CO3, N2O5, HNO3, SO4^2-, Fe3+. Capitals matter: Co is cobalt, CO is carbon monoxide.
- Cation
- Anion
Everything is calculated in your browser, so results appear instantly and nothing you type is sent to a server.
How it works
The formula is first compared with a list of compounds that have established names, then tested as an ion, an acid (hydrogen plus a known anion), an ionic compound (every way of splitting it into a known cation and anion whose charges cancel – fixed-charge metals must match, common oxidation states are preferred) and finally as a binary molecular compound named with prefixes.
Worked example
Name Fe₂(SO₄)₃. Iron is a metal and SO₄ is the sulfate ion, SO₄²⁻, so this is an ionic compound. Three sulfates carry 3 × (−2) = −6, which two iron ions must balance: each is +6/2 = +3. Iron has more than one common charge, so the name needs a Roman numeral: iron(III) sulfate (traditional: ferric sulfate). Its molar mass is 2 × 55.845 + 3 × 96.06 = 399.87 g/mol.
Second example: N₂O₄ contains only non-metals, so it is molecular: “di” for the two nitrogens and “tetra” for the four oxygens, with the final “a” dropped before “oxide” – dinitrogen tetroxide.
Common polyatomic ions
| Ion | Name | Acid |
|---|---|---|
| NH₄⁺ | ammonium | – |
| OH⁻ | hydroxide | – |
| NO₃⁻ / NO₂⁻ | nitrate / nitrite | nitric / nitrous acid |
| SO₄²⁻ / SO₃²⁻ | sulfate / sulfite | sulfuric / sulfurous acid |
| CO₃²⁻ / HCO₃⁻ | carbonate / hydrogen carbonate | carbonic acid |
| PO₄³⁻ | phosphate | phosphoric acid |
| ClO⁻ / ClO₂⁻ / ClO₃⁻ / ClO₄⁻ | hypochlorite / chlorite / chlorate / perchlorate | hypochlorous / chlorous / chloric / perchloric acid |
| MnO₄⁻ | permanganate | permanganic acid |
| Cr₂O₇²⁻ | dichromate | dichromic acid |
| CH₃COO⁻ | acetate | acetic acid |
Tips
- Type formulas with normal capitals and numbers, e.g. Ca(OH)2 or CuSO4·5H2O – brackets and hydrates work.
- Atomic masses are IUPAC standard atomic weights; radioactive elements use the mass number of their longest-lived isotope.
- Electronegativity values are on the Pauling scale.
- Everything is calculated in your browser.
Common mistakes to avoid
- Writing CO (carbon monoxide) when you mean Co (cobalt) – capitals matter.
- Forgetting to multiply the bracket contents by the subscript after the bracket.
- Mixing up atomic number (protons) and mass number (protons + neutrons).
Formula
Ionic: cation name (+ Roman numeral for variable charge) + anion name · Σ charges = 0Molecular: prefix + first element + prefix + root of second element + “-ide”Acids: hydro-…-ic (from -ide), …-ic (from -ate), …-ous (from -ite)Worked example
Inputs — Mode: Formula → name; Chemical formula: Fe2(SO4)3.
Results — Name = iron(III) sulfate; Formula = Fe₂(SO₄)₃; Traditional / common name = ferric sulfate; Type of compound = Ionic compound with a polyatomic ion; Ions and charges = Fe³⁺ × 2 + SO₄²⁻ × 3 (charges: 2 × (+3) + 3 × (-2) = 0); Molar mass = 399.858 g/mol.
Key terms
- Cation
- A positively charged ion, such as Na⁺, Fe³⁺ or NH₄⁺.
- Anion
- A negatively charged ion, such as Cl⁻, O²⁻ or SO₄²⁻.
- Polyatomic ion
- A charged group of covalently bonded atoms that acts as one ion, such as nitrate (NO₃⁻).
- Stock system
- Naming that shows a metal’s charge with Roman numerals, e.g. iron(III).
- Oxyanion
- A polyatomic anion containing oxygen; -ate and -ite forms differ by one oxygen atom.
Frequently asked questions
How do you name an ionic compound?
Name the cation, then the anion. If the metal has more than one common charge, add it in Roman numerals: CuO is copper(II) oxide because one O²⁻ needs a Cu²⁺; Cu₂O is copper(I) oxide.
When do I use Roman numerals?
For metals with variable charge – most transition metals plus tin, lead and mercury. Group 1 and 2 metals, aluminium, zinc, cadmium and silver have one common charge and get no numeral.
How do you name covalent compounds?
Use Greek prefixes for the number of atoms (mono, di, tri, tetra, penta, hexa, hepta, octa, nona, deca) and end the second element in “-ide”. Mono- is never used on the first element: CO₂ is carbon dioxide, P₄O₁₀ tetraphosphorus decoxide.
What is the name of Fe₂(SO₄)₃?
Iron(III) sulfate (traditional name ferric sulfate). Three sulfate ions carry −6, so each of the two iron ions is +3.
How are acids named?
Hydrogen + an “-ide” anion gives hydro-…-ic acid (HCl, hydrochloric acid); an “-ate” anion gives an “-ic” acid (H₂SO₄, sulfuric acid); an “-ite” anion gives an “-ous” acid (HNO₂, nitrous acid).
How do I name a hydrate?
Name the salt and add a prefix plus “hydrate” for the water molecules: CuSO₄·5H₂O is copper(II) sulfate pentahydrate.
What is the difference between ferrous and ferric?
They are the older names for iron(II) and iron(III). The “-ous” ending marks the lower charge and “-ic” the higher one, as in cuprous/cupric and stannous/stannic.
Can it name organic compounds?
Only common ones such as methane, ethanol, acetic acid or glucose. Organic names depend on how the atoms are connected, which a molecular formula alone does not show.
What formula does the Chemical Name Calculator use?
Ionic: cation name (+ Roman numeral for variable charge) + anion name · Σ charges = 0.