Naming Binary Compounds of Metals and Nonmetals Presentation

Topic 1 · Ionic naming

Naming Binary Compounds of Metals and Nonmetals

Binary ionic compounds contain two elements: a metal cation and a nonmetal anion. Their names are built from ion identities and charge balance.

metal first nonmetal becomes -ide Roman numerals when needed

Learning target

Identify the metal and nonmetal ions, determine whether a Roman numeral is needed, and write the correct name from a binary ionic formula.

FeCl₃

iron(III) chloride

Why it matters

Names communicate composition and charge.

A compound name is not just a label. It tells chemists which ions are present and, for variable-charge metals, which charge the metal has in that formula unit.

Laboratory communication

“Copper(I) chloride” and “copper(II) chloride” describe different compounds.

Formula interpretation

Subscripts reveal the charge ratio needed to make a neutral formula unit.

Problem solving

Naming rules connect periodic table patterns, ionic charges, and formula writing.

Core concept

A binary ionic name follows a predictable pattern.

Name the metal cation first. Then name the nonmetal anion by changing its ending to -ide. Add a Roman numeral only when the metal can form more than one charge.

1. Find the metal

The metal is the cation and is written first in the formula.

2. Find the nonmetal

The nonmetal is the anion and is written second.

3. Check metal charge

Variable-charge metals require Roman numerals.

4. Name the anion

Change the nonmetal ending to -ide.

Pattern: metal name + optional Roman numeral + nonmetal root + ide.

Vocabulary

Charge patterns tell you when Roman numerals are needed.

Many main-group metals have predictable fixed charges. Many transition metals can form more than one cation, so the name must state the charge.

Term	Meaning	Example	Naming rule
Metal cation	Positive ion formed by a metal	Na⁺, Mg²⁺, Fe³⁺	Name the metal first.
Nonmetal anion	Negative ion formed by a nonmetal	Cl⁻, O²⁻, N³⁻	Change ending to -ide.
Fixed-charge metal	Metal with one common charge	Na⁺, Ca²⁺, Al³⁺	No Roman numeral.
Variable-charge metal	Metal with more than one possible charge	Fe²⁺ or Fe³⁺	Use Roman numeral.
Formula unit	Lowest whole-number ratio of ions in an ionic compound	MgCl₂	Total charge must be zero.

Main rule

Charge balance explains the formula and the name.

Ionic compounds are electrically neutral. The total positive charge from cations must equal the total negative charge from anions.

\[ \text{total positive charge} + \text{total negative charge} = 0 \]

For MgCl₂, Mg is Mg²⁺ and each chloride is Cl⁻. One Mg²⁺ balances two Cl⁻ ions, so the name is magnesium chloride.

Fixed-charge example

NaCl is sodium chloride. Sodium is always Na⁺ in this context, so no Roman numeral is needed.

Variable-charge example

FeCl₃ is iron(III) chloride because three chloride ions require Fe³⁺.

Interactive simulation

Choose ions and build the compound name.

Select a metal ion and a nonmetal ion. The simulation balances charges, writes the formula unit, and builds the correct name.

Ion name builder

Metal cation

Nonmetal anion

Balanced formula and name

MgCl₂ — magnesium chloride

Total charge: +2 and −2, so the formula unit is neutral.

Static fallback model

Mg²⁺ needs two Cl⁻ ions for charge balance. The formula is MgCl₂, and the name is magnesium chloride.

Cation

Mg2+

+

Anion

2 Cl−

Dynamic relationship

The formula is the smallest neutral charge combination.

The graph shows how many cations and anions are required to make the total positive and total negative charges equal in magnitude.

This visual uses the ion choices from the interactive builder.

Worked example

Name FeCl₃.

The formula contains a metal, Fe, and a nonmetal, Cl. Chlorine forms chloride, Cl⁻. Use charge balance to find the iron charge.

1

Identify the ions

Fe is the metal cation. Cl is the nonmetal anion and becomes chloride.

2

Find the metal charge

Three Cl⁻ ions give a total charge of −3, so iron must be Fe³⁺.

3

Use a Roman numeral

Iron is a variable-charge metal, so Fe³⁺ is written as iron(III).

Final answer: FeCl₃ is iron(III) chloride.

Common mistake

Do not use Roman numerals for fixed-charge metals.

Roman numerals are not used for metals with predictable fixed charges, such as Group 1, Group 2, aluminum, zinc, silver, and cadmium in introductory naming.

Incorrect reasoning

“MgCl₂ is magnesium(II) chloride because Mg has a 2+ charge.”

The charge is true, but the naming rule is wrong.

Correct reasoning

Magnesium is a fixed-charge Group 2 metal. The correct name is magnesium chloride, with no Roman numeral.

Practice check

Name CuO.

Question: What is the correct name of CuO?

Show answer

1

Identify the anion

Oxygen forms oxide, O²⁻.

2

Find the copper charge

There is one oxide ion with charge −2, so copper must be Cu²⁺.

3

Name the compound

Copper is variable-charge, so use copper(II). The name is copper(II) oxide.

Reasonableness check

Cu⁺ would need only half an oxide ion to balance O²⁻, which is impossible. One Cu and one O means copper is 2+.

Apply the topic

Use charge balance to move between formulas and names.

Binary ionic naming becomes reliable when you always identify the ions, balance charge, and decide whether the metal needs a Roman numeral.

Open the calculator

Practice naming binary ionic compounds from formulas and ion charges.

Try related questions

Check your understanding of fixed-charge metals, variable-charge metals, and -ide endings.

Metal

Name first.

Charge

Add Roman numeral if needed.

Nonmetal

Change ending to -ide.

Formula unit

Confirm charge neutrality.

Final summary

Binary ionic names are built from ions and charge balance.

Metal first

Name the metal cation first, using the element name.

Nonmetal second

Name the nonmetal anion with the -ide ending.

Roman numerals

Use Roman numerals only for variable-charge metals.

Neutral formula units

Subscripts come from the smallest whole-number charge balance.

Key idea: The correct name communicates both the ion identities and, when necessary, the metal ion charge.