Naming Binary Compounds of Nonmetals Presentation

Topic 1 · Molecular naming

Naming Binary Compounds of Nonmetals

Binary molecular compounds contain two nonmetals. Their names use Greek prefixes to show the exact number of atoms in the molecular formula.

two nonmetals Greek prefixes second element ends in -ide

Learning target

Use element order, prefixes, and the -ide ending to write names from formulas and formulas from names.

N₂O₅

dinitrogen pentoxide

Why it matters

Prefixes prevent different molecules from having the same name.

Carbon and oxygen can form CO and CO₂. Without prefixes, their names would not show the different atom counts that make them different substances.

Exact composition

Prefixes tell the number of atoms in each molecule, not just which elements are present.

Molecular identity

Carbon monoxide and carbon dioxide have different formulas, properties, and names.

Formula writing

A name such as sulfur hexafluoride directly encodes SF₆.

Core concept

Binary molecular names are count-based, not charge-based.

Ionic names depend on charges. Molecular names depend on the actual number of atoms shown by the formula subscripts.

1. Confirm nonmetals

The formula should contain two nonmetals.

2. Name first element

Use a prefix only if there is more than one atom.

3. Name second element

Always use a prefix for the second element.

4. Add -ide

Change the second element ending to -ide.

Pattern: prefix + first element name + prefix + second element root + ide.

Vocabulary

Greek prefixes are the counting language of molecular formulas.

Prefixes match subscripts. The first element usually drops mono-, but the second element uses mono- when there is one atom.

Number	Prefix	Formula example	Name example
1	mono-	CO	carbon monoxide
2	di-	CO₂	carbon dioxide
3	tri-	NCl₃	nitrogen trichloride
4	tetra-	CCl₄	carbon tetrachloride
5	penta-	N₂O₅	dinitrogen pentoxide
6	hexa-	SF₆	sulfur hexafluoride
7–10	hepta-, octa-, nona-, deca-	Cl₂O₇	dichlorine heptoxide

Main rule

Subscripts become prefixes.

A subscript tells how many atoms of that element are in one molecule. Molecular names translate those subscripts into Greek prefixes.

\[ \text{subscript count} \rightarrow \text{Greek prefix in the name} \]

For N₂O₅, the subscript 2 gives dinitrogen, and the subscript 5 gives pentoxide. The full name is dinitrogen pentoxide.

First element

Do not use mono- on the first element. CO is carbon monoxide, not monocarbon monoxide.

Second element

Always use a prefix and change the ending to -ide: oxygen becomes oxide, chlorine becomes chloride.

Interactive simulation

Build a binary molecular formula and name it.

Choose two nonmetals and set their atom counts. The simulation turns subscripts into prefixes and builds the molecular name.

Molecular name builder

First nonmetal

Second nonmetal

First element atoms: 2

Second element atoms: 5

Formula and name

N₂O₅ — dinitrogen pentoxide

Prefixes show 2 nitrogen atoms and 5 oxygen atoms.

Static fallback model

N₂O₅ contains two nitrogen atoms and five oxygen atoms, so its name is dinitrogen pentoxide.

N N O O O O O

The model shows atom counts, not the real molecular geometry.

Dynamic relationship

Changing subscripts changes both formula and name.

The graph compares atom counts and shows the prefix assigned to each subscript. This reinforces that molecular naming is count-based.

This visual uses the molecule built on the interactive slide.

Worked example

Name PCl₅.

The formula contains phosphorus and chlorine, both nonmetals. Use molecular prefixes instead of ionic charges.

1

Name the first element

The first element is phosphorus. Because there is only one phosphorus atom, do not use mono-.

2

Name the second element with a prefix

There are five chlorine atoms, so use penta- and change chlorine to chloride.

3

Combine the parts

phosphorus + pentachloride gives phosphorus pentachloride.

Final answer: PCl₅ is phosphorus pentachloride.

Common mistake

Do not use ionic charge rules for two nonmetals.

Binary molecular formulas do not need charge balancing or Roman numerals. Their names come from atom counts.

Incorrect reasoning

“N₂O₅ should be nitrogen(V) oxide because oxygen is 2−.”

That uses ionic naming on a molecular compound.

Correct reasoning

Both elements are nonmetals, so use prefixes: dinitrogen pentoxide.

Practice check

Name SF₆.

Question: What is the correct name of SF₆?

Show answer

1

Identify compound type

Sulfur and fluorine are nonmetals, so this is a binary molecular compound.

2

Name the first element

One sulfur atom is written as sulfur, not monosulfur.

3

Name the second element

Six fluorine atoms use hexa-, and fluorine becomes fluoride.

Answer: SF₆ is sulfur hexafluoride.

Reasonableness check

The subscript 6 must appear in the name as hexa-. Without the prefix, the name would not communicate the exact molecular formula.

Apply the topic

Use prefixes whenever the compound is made of two nonmetals.

Before naming, classify the formula. Metal + nonmetal usually uses ionic naming. Nonmetal + nonmetal uses molecular prefixes.

Open the calculator

Practice naming binary molecular compounds from formulas and prefixes.

Try related questions

Check your ability to use Greek prefixes, element order, and -ide endings.

Classify

Two nonmetals means molecular naming.

Count atoms

Read subscripts directly.

Add prefixes

Use mono-, di-, tri-, and beyond.

End with -ide

Modify the second element name.

Final summary

Binary molecular names translate subscripts into prefixes.

Two nonmetals

Use molecular naming rules, not ionic charge rules.

Prefixes show counts

Di-, tri-, tetra-, and other prefixes match formula subscripts.

First mono- is omitted

CO is carbon monoxide, not monocarbon monoxide.

Second element ends in -ide

Oxygen becomes oxide, fluorine becomes fluoride, and chlorine becomes chloride.

Key idea: Molecular names communicate exact atom counts, so changing a subscript changes the compound name.