Last updated: July 3, 2026
Chemical Name Calculator
Creators
Dharmendra SinghReviewers
Creators
Dharmendra SinghReviewers
Quick Answer
The chemical name calculator uses a deterministic ion lookup table and the criss-cross method to name common ionic compounds. For cation charge p and anion charge q, it returns cation subscript q/gcd(p,q), anion subscript p/gcd(p,q), the neutral formula, and the compound name.
To name an ionic compound, choose the cation and anion, reduce their charge magnitudes to the lowest whole-number ratio, write the neutral formula, and say the cation name followed by the anion name. For aluminium sulfate, Al three plus and sulfate two minus make Al two sulfate three, named aluminium sulfate.
Key Takeaways
- Ionic formulas must have zero net charge.
- Criss-cross charge magnitudes, then reduce subscripts by gcd(p,q).
- Polyatomic ions stay intact and get parentheses only when their count is greater than one.
- The compound name is cation name followed by anion name.
- Transition-metal names need Roman numerals when multiple charges are possible.
Creators
Dharmendra SinghReviewers
Creators
Dharmendra SinghReviewers
Formula
cation subscript = q/gcd(p,q); anion subscript = p/gcd(p,q)
Where:
- p=Cation charge magnitude(charge units)
- q=Anion charge magnitude(charge units)
- gcd(p,q)=Greatest common divisor of the charge magnitudes(charge units)
- n=Reduced formula subscript(count)
Worked Examples
Sodium chloride
A +1 sodium ion and a −1 chloride ion combine in a one-to-one ratio.
- 1Set p = 1 for Na⁺ and q = 1 for Cl⁻.
- 2gcd(1,1)=1, so the cation subscript is 1/1 = 1 and the anion subscript is 1/1 = 1.
- 3Write one Na and one Cl with no visible 1 subscripts.
- 4Name the compound by cation then anion: sodium chloride.
Calcium chloride
Calcium is +2 and chloride is −1, so two chloride ions are required.
- 1Set p = 2 for Ca²⁺ and q = 1 for Cl⁻.
- 2gcd(2,1)=1, so Ca gets subscript 1 and Cl gets subscript 2.
- 3The neutral formula is CaCl₂ because +2 and 2×(−1) cancel.
- 4Name the compound calcium chloride.
Aluminium oxide
Aluminium is +3 and oxide is −2, giving the classic Al₂O₃ ratio.
- 1Set p = 3 for Al³⁺ and q = 2 for O²⁻.
- 2gcd(3,2)=1, so Al gets subscript 2 and O gets subscript 3.
- 3Check neutrality: 2×(+3)=+6 and 3×(−2)=−6.
- 4Name the compound aluminium oxide.
Aluminium sulfate
A polyatomic sulfate ion needs parentheses when three sulfate groups are present.
- 1Set p = 3 for Al³⁺ and q = 2 for SO₄²⁻.
- 2gcd(3,2)=1, so the subscripts are Al₂ and (SO₄)₃.
- 3Put sulfate in parentheses because the polyatomic ion count is greater than 1.
- 4Name the compound aluminium sulfate.
Ammonium sulfate
Both ions include a polyatomic ion, but only ammonium repeats.
- 1Set p = 1 for NH₄⁺ and q = 2 for SO₄²⁻.
- 2gcd(1,2)=1, so ammonium gets subscript 2 and sulfate gets subscript 1.
- 3Write repeated ammonium as (NH₄)₂, while a single sulfate needs no parentheses.
- 4Name the compound ammonium sulfate.
Introduction
The chemical name calculator names common ionic compounds and builds their neutral formulas from a selected cation and anion. It applies the classroom criss-cross method rigorously: take the positive and negative charge magnitudes, reduce by their greatest common divisor, and use the opposite charge as each ion's subscript. This complements formula-focused tools such as the molar mass calculator and the atom calculator, while following naming principles described by IUPAC and open chemistry texts such as OpenStax Chemistry 2e.
What the calculator does
Choose one supported cation and one supported anion. The calculator looks up each ion's symbol, charge magnitude, and name, then returns a compound name, a charge-balanced formula, and the reduced subscripts. It is intentionally deterministic: sodium always means Na⁺, sulfate always means SO₄²⁻, and iron(III) always means Fe³⁺.
Criss-cross formula method
For a cation charge magnitude p and an anion charge magnitude q, the raw criss-cross subscripts are q and p. The chemically correct formula uses the lowest whole-number ratio, so both are divided by gcd(p,q). For Al³⁺ and SO₄²⁻, gcd(3,2)=1, so the formula is Al₂(SO₄)₃. For Ca²⁺ and CO₃²⁻, gcd(2,2)=2, so the reduced formula is CaCO₃ rather than Ca₂(CO₃)₂.
How ionic names are assembled
Binary and polyatomic ionic compound names normally put the cation name first and the anion name second: sodium chloride, calcium carbonate, aluminium sulfate. Monatomic anions use the familiar -ide ending, while polyatomic anions keep standard names such as nitrate, sulfate, carbonate, phosphate, hydroxide, and bicarbonate. Transition-metal entries include the Roman numeral because Fe²⁺ and Fe³⁺ form different compounds.
When parentheses are needed
Parentheses are used only when a polyatomic ion appears more than once in the formula. One sulfate group in CaSO₄ needs no parentheses, but three sulfate groups in Al₂(SO₄)₃ do. Similarly, ammonium sulfate is (NH₄)₂SO₄ because two ammonium groups are required. After formula construction, the percent composition calculator can use the same formula to analyze mass fractions.
Checking neutrality
Every ionic formula unit must have a net charge of zero. Multiply the cation subscript by the cation charge and the anion subscript by the anion charge; the magnitudes should match. FeCl₃ is neutral because Fe³⁺ contributes +3 and three Cl⁻ ions contribute −3. For amount calculations after naming, use the mole calculator or molar mass calculator.
Scope and data quality
The lookup table covers common introductory chemistry ions: alkali metals, alkaline-earth ions, aluminium, ammonium, selected transition-metal cations, halides, oxide, sulfide, hydroxide, nitrate, sulfate, carbonate, phosphate, and bicarbonate. Names and formulas align with conventions in LibreTexts nomenclature resources and the NIST Chemistry WebBook where compound records are available.
Quick Reference Card
Ionic Naming Quick Reference
Quick reference • Chemical Name Calculator
n(cation)=q/gcd(p,q); n(anion)=p/gcd(p,q)Valid range: Common monoatomic and polyatomic ions in the built-in lookup table; output formulas are reduced neutral formula units.
Common Values
⚠ Watch Out
- •Always reduce subscripts to the lowest whole-number ratio.
- •Do not alter atoms inside a polyatomic ion such as NO₃⁻ or SO₄²⁻.
- •Use parentheses only for repeated polyatomic ions, not for single groups.
- •Choose the correct transition-metal charge before naming the compound.
Pro Tips
- →Check neutrality by multiplying each subscript by its ion charge.
- →Remember that a missing subscript means 1.
- →For equal charge magnitudes like Ca²⁺ and CO₃²⁻, the formula ratio is 1:1.
- →After building a formula, use molar mass to connect the name to lab quantities.
FAQs
What is the criss-cross method?
It is a shortcut for balancing ionic charges. The cation charge magnitude becomes the anion subscript, the anion charge magnitude becomes the cation subscript, and the ratio is reduced to lowest whole numbers.
Why is calcium carbonate CaCO₃ instead of Ca₂(CO₃)₂?
Calcium is +2 and carbonate is −2. The gcd is 2, so both raw subscripts reduce from 2:2 to 1:1, giving CaCO₃.
When do I use Roman numerals in names?
Use Roman numerals for metals with variable charges. This calculator includes Iron(II), Iron(III), and Copper(II), so FeCl₃ is named Iron(III) chloride.
Do polyatomic ions change internally during criss-crossing?
No. Keep the ion intact. Sulfate remains SO₄ and ammonium remains NH₄; only the number of whole ion groups changes.
Why are parentheses added around some ions?
Parentheses show that more than one whole polyatomic ion is present, as in Al₂(SO₄)₃ or (NH₄)₂SO₄. They are not used for a single polyatomic ion.
Can this name covalent molecules?
No. It is designed for common ionic compounds. Molecular prefix names such as carbon dioxide or dinitrogen tetroxide follow different covalent naming rules.