Chemical Name Calculator
Build an ionic compound name and charge-balanced formula from common cations and anions, with optional hydrate notation.
01 Set up your calculation
- Select the positive and negative ions. For a metal with several listed charges, choose the intended Stock numeral, such as iron(II) or iron(III).
- Leave water at 0 for the formula without added water. Enter 1–10 only when that hydrate composition is specified.
- Read the name, the smallest neutral ion ratio, and the formula. The molar mass includes any water you entered.
02 The relationship
For the assumptions behind these results, read the explanation below. You can also explore Molar Mass and Percent Composition.
Follow the numbers
Calcium is Ca²⁺ and phosphate is PO₄³⁻. Three calcium ions contribute +6 and two phosphate ions contribute −6, giving Ca3(PO4)2, calcium phosphate. Its formula contains 3 Ca, 2 P and 8 O atoms, for a molar mass of 310.174 g/mol with the rounded weights used here.
03 Balance ion charges without changing the ions
Begin with the charge of each selected ion, then find the smallest total charge they can cancel. Equal charges such as Mg²⁺ and O²⁻ need a 1:1 ratio, so the formula is MgO rather than Mg2O2. A 3+ ion and a 2− ion need a 2:3 ratio.
Parentheses keep repeated polyatomic ions together. Aluminum sulfate is Al2(SO4)3: the subscript outside the parentheses multiplies the entire sulfate group. Do not reduce the internal subscripts of an ion. Peroxide remains O2²⁻, and mercury(I) remains the two-atom ion Hg2²⁺.
04 Read the name as a composition label
The positive-ion name comes first, followed by the negative-ion name. A Stock numeral identifies the metal oxidation state, not the number of atoms: iron(II) chloride is FeCl2, while iron(III) chloride is FeCl3. Familiar fixed-charge ions such as sodium and calcium are listed without numerals.
Polyatomic names are retained. Sulfate and sulfite, for example, contain different numbers of oxygen atoms and must be selected separately. Hydrogen carbonate is also commonly called bicarbonate. The name here describes the chosen ions; it does not identify a substance from an unknown formula or trade name.
05 Add hydrate water only when it is known
Hydrate notation records water included in the stated crystal composition. Five waters after copper(II) sulfate produce CuSO4·5H2O and the name copper(II) sulfate pentahydrate. The water count is per neutral formula unit, after the ion ratio has been reduced.
Water changes the formula mass but contributes no net charge. It is not the volume of solvent added to dissolve a sample. The calculator accepts a specified count; it does not predict which hydrate forms, or whether a particular hydrate can exist under your conditions.
06 What a valid formula establishes
A neutral charge balance is a nomenclature result, not evidence that an isolable compound exists. Some selected pairs may react, decompose, form complexes, or behave differently from a simple ionic model. Solubility, stability, bonding character and crystal structure require separate information.
This tool covers the listed cations and anions and integer hydrates through ten waters. It does not name arbitrary organic molecules, covalent compounds, mixed-cation salts or coordination complexes. Molar masses use rounded average atomic weights and are not isotope-specific exact masses.
Questions from the notebook
Why does calcium phosphate need parentheses?
The two phosphate units each contain one phosphorus and four oxygen atoms. Ca3(PO4)2 preserves those groups, giving a total of two phosphorus and eight oxygen atoms.
Does a Roman numeral count the metal atoms?
No. It identifies the oxidation state. In Fe2(SO4)3, each iron is in the +3 state, so the name is iron(III) sulfate even though the formula contains two iron atoms.
Why does mercury(I) have a 2+ ion charge?
The listed mercury(I) ion is Hg2²⁺. It contains two mercury atoms, each with oxidation state +1. The complete ion therefore carries +2, and its Hg2 group must stay intact.
Can I paste a formula and get its name?
This calculator builds a name and formula from selected ions. It does not perform a universal formula-to-name lookup. For a formula you already know, the molar mass calculator can check its elemental composition.
Does choosing a hydrate mean that hydrate is real?
No. The tool writes the composition you specify. Confirm a material’s hydrate form from its documented composition before using the resulting molar mass.
References & reading
- OpenStax, Rice University — Chemistry 2e: Ionic and Molecular Compounds ↗
Figure 2.29 and Table 2.5 supply common ion charges and polyatomic formulas; the chapter explains charge-neutral formula ratios and limits of ionic classification.
- OpenStax, Rice University — Chemistry 2e: Chemical Nomenclature ↗
Supports cation–anion naming, Stock numerals, the mercury(I) dimer, tin charge states, polyatomic parentheses and hydrate names through decahydrate.
- OpenStax, Rice University — Chemistry 2e: Formula Mass and the Mole Concept ↗
Explains summing the atomic-mass contributions in a formula to obtain formula mass and molar mass.
- NIST — Atomic Weights and Isotopic Compositions ↗
Provides atomic-weight and isotope context. The site uses rounded conventional weights for its approximate molar-mass calculation.
Our explanations are written for ChemistryCalc. Read how we build and check our tools. These calculations are educational estimates where the underlying model requires assumptions.