Chemical Name Calculator

Name any ionic compound from its cation and anion, by symbol or by name.

Covers 33 cations and 38 anions, including polyatomic ions.

Updated August 23, 2026

CreatorFrank Zhao

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Introduction

Every ionic compound is built from a positively charged cation and a negatively charged anion, held together by the attraction between opposite charges. The tricky part is figuring out how many of each you need so the compound is electrically neutral — and then turning that ratio into a proper name and formula.

This calculator does both in one step. Pick a cation and an anion — by their symbols (like $\mathrm{Na^+}$ ) or by their names (like Sodium) — and it instantly shows the neutral compound's formula and its systematic name. It covers 33 common cations and 38 anions, including the polyatomic ions that tend to trip people up.

Who is this for? Students checking homework, anyone who needs to write a formula from a name (or a name from a formula), and people who just want to double-check a compound they came across in a label or a textbook.

How to use

Choose how you want to search: formula to pick ions by their symbols (like $\mathrm{Na^+}$ ), or name to pick them by their names (like Sodium).

Pick the cation — the positive ion. For example, Sodium ( $\mathrm{Na^+}$ ).

Pick the anion — the negative ion. For example, Chloride ( $\mathrm{Cl^-}$ ).

Read the result: the compound's name and its formula. The subscripts are already reduced to the smallest whole numbers that balance the charges.

Worked example — table salt

Search by formula, then pick Na⁺ as the cation.
Pick Cl⁻ as the anion.

\mathrm{Na^+}

+

\mathrm{Cl^-}

\rightarrow

\mathrm{NaCl}

The result reads Sodium Chloride with the formula NaCl — one sodium ion balances one chloride ion.

Calculation method

An ionic compound must be electrically neutral: the total positive charge has to exactly balance the total negative charge. The subscripts in the formula are the smallest whole numbers that make that balance work.

The classic shortcut is the cross-over method: the subscript on the cation is the magnitude of the anion's charge, and the subscript on the anion is the magnitude of the cation's charge. The calculator applies this and then divides both by the greatest common divisor so the ratio is always in its simplest form:

n_{\mathrm{cation}}

=

\frac{q_{\mathrm{anion}}}{\gcd(q_{\mathrm{cation}},\ q_{\mathrm{anion}})}

n_{\mathrm{anion}}

=

\frac{q_{\mathrm{cation}}}{\gcd(q_{\mathrm{cation}},\ q_{\mathrm{anion}})}

Where:

$q_{\mathrm{cation}}$ — charge of the cation (e.g. 3 for $\mathrm{Al^{3+}}$ )
$q_{\mathrm{anion}}$ — charge of the anion (e.g. 2 for $\mathrm{O^{2-}}$ )
$n_{\mathrm{cation}}$ and $n_{\mathrm{anion}}$ — the subscripts in the formula

Example — aluminum oxide (Al₂O₃)

Aluminum forms $\mathrm{Al^{3+}}$ and oxygen forms $\mathrm{O^{2-}}$ . The cross-over gives Al₂O₃:

n_{\mathrm{Al}}

=

\frac{2}{\gcd(3,2)}

=

\frac{2}{1}

=

2

n_{\mathrm{O}}

=

\frac{3}{\gcd(3,2)}

=

\frac{3}{1}

=

3

Result: Al₂O₃, named Aluminum Oxide.

Why subscripts get reduced — calcium oxide (CaO)

When both ions have the same charge, the cross-over would suggest Ca₂O₂ — but the simplest neutral ratio is CaO. The calculator divides by the GCD to avoid the doubled-up formula:

n_{\mathrm{Ca}}

=

\frac{2}{\gcd(2,2)}

=

\frac{2}{2}

=

1

Result: CaO, named Calcium Oxide — not Ca₂O₂.

Parentheses for polyatomic ions: when a polyatomic ion appears more than once, it is wrapped in parentheses. For example, ammonium ( $\mathrm{NH_4^+}$ ) with sulfate ( $\mathrm{SO_4^{2-}}$ ) gives (NH₄)₂SO₄ — the sulfate ion appears twice, so it is written in parentheses with a subscript 2.

Roman numerals for transition metals: metals like iron can form ions with different charges, so the name must say which one. Iron(II) is $\mathrm{Fe^{2+}}$ and Iron(III) is $\mathrm{Fe^{3+}}$ . The calculator applies these Roman numerals automatically from the ion you select. This convention follows the IUPAC recommendations for inorganic nomenclature.

Real-world examples

Ammonium sulfate — (NH₄)₂SO₄

A common nitrogen and sulfur fertilizer. Ammonium is $\mathrm{NH_4^+}$ (charge 1) and sulfate is $\mathrm{SO_4^{2-}}$ (charge 2).

n_{\mathrm{NH_4}}

=

\frac{2}{\gcd(1,2)}

=

2

Two ammonium ions balance one sulfate ion, so the formula is (NH₄)₂SO₄ — Ammonium Sulfate.

Iron(III) oxide — Fe₂O₃

The reddish-brown rust that forms on iron. Iron(III) is $\mathrm{Fe^{3+}}$ (charge 3) and oxide is $\mathrm{O^{2-}}$ (charge 2).

n_{\mathrm{Fe}}

=

\frac{2}{\gcd(3,2)}

=

2

n_{\mathrm{O}}

=

\frac{3}{\gcd(3,2)}

=

3

Result: Fe₂O₃ — Iron(III) Oxide. The Roman numeral (III) is essential here because iron also forms Fe²⁺.

Tips & best practices

Always reduce the ratio

The formula must use the smallest whole-number subscripts. Ca²⁺ + O²⁻ is CaO, not Ca₂O₂. The calculator does this reduction for you.

Watch for parentheses

A polyatomic ion that appears more than once goes in parentheses: Mg²⁺ + OH⁻ gives Mg(OH)₂, not MgOH₂.

Check transition-metal charges

Iron, copper, lead and others form more than one ion. The Roman numeral in the name (II, III, IV) tells you which charge was used.

Verify with the periodic table

If you are unsure of an ion’s charge, check the group number or the ion’s known charge before trusting the result.

Once you have the name and formula, a natural next step is working out the compound's mass. The Molar Mass Calculator turns any formula into grams per mole, which you need for preparing solutions or converting between mass and moles.

Frequently asked questions

Why do some formulas have parentheses?

Parentheses are used when a polyatomic ion (a group of atoms that acts as a single ion) appears more than once. For example, calcium and hydroxide give Ca(OH)₂ — the OH group appears twice, so it is wrapped in parentheses with a subscript 2. Without the parentheses, CaOH₂ would look like a different compound.

Why do some metals have Roman numerals in their names?

Transition metals can form ions with different charges. Iron can be $\mathrm{Fe^{2+}}$ or $\mathrm{Fe^{3+}}$ , so the name must say which one: Iron(II) or Iron(III). The Roman numeral is the charge of the ion used in that compound.

Can this calculator name covalent compounds?

No. Covalent compounds (made from two non-metals, like CO₂ or H₂O) use a different naming system with prefixes such as mono-, di- and tri-. This calculator handles ionic compounds only, where a metal or ammonium cation combines with an anion.

Limitations

•The calculator covers the 33 cations and 38 anions in its lists. Ions outside these lists (for example, less common polyatomic ions) cannot be entered.
•It names ionic compounds only. Covalent compounds, acids, hydrates and organic compounds follow different naming rules and are not covered.
•This is an educational tool. For graded work or anything where a name or formula must be exact, double-check the result against a textbook or your instructor.

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