Chemistry · 9th Grade · Chemical Bonding and Molecular Geometry · Weeks 1-9

Nomenclature of Covalent Compounds and Acids

Students will learn to name and write formulas for binary covalent compounds and common acids.

• Common Core State Standards
• HS-PS1-2
• STD.CCSS.ELA-LITERACY.L.9-10.6

About This Topic

Covalent nomenclature follows a different logic from ionic nomenclature: because two nonmetals can combine in many possible ratios, prefixes (mono-, di-, tri-, tetra-, penta-...) specify the exact number of each atom. Binary covalent compounds like dinitrogen tetroxide (N₂O₄) and sulfur hexafluoride (SF₆) require students to apply prefixes systematically and to drop redundant vowels where the prefix ends in a vowel and the element name begins with one , 'monoxide' not 'monooxide.'

Acids introduce a second naming convention based on whether the acid contains oxygen. Binary acids use the 'hydro-___-ic acid' pattern, while oxyacids derive their names from the polyatomic ion they release: '-ate' ions yield '-ic acid' and '-ite' ions yield '-ous acid.' Students who have already mastered ionic nomenclature find this connection between polyatomic ion names and oxyacid names rewarding , the prior knowledge transfers directly.

This topic is highly procedural, and students benefit from step-by-step frameworks they can apply independently rather than case-by-case memorization. Active learning strategies that require students to articulate their decision-making , not just produce an answer , build the metacognitive habits needed for flexible rule application on assessments.

Key Questions

1. Construct the chemical formula for a covalent compound given its name.
2. Differentiate between the naming conventions for binary covalent compounds and binary acids.
3. Explain the importance of prefixes in naming covalent compounds.

Learning Objectives

• Construct the chemical formula for binary covalent compounds given their IUPAC name, applying prefix rules.
• Differentiate between the naming conventions for binary covalent compounds and binary acids.
• Explain the role of prefixes in accurately representing the stoichiometry of binary covalent compounds.
• Write the IUPAC name for common binary acids and oxyacids based on their chemical formulas.
• Classify compounds as binary covalent, binary acid, or oxyacid based on their constituent elements and structure.

Before You Start

Introduction to Chemical Formulas

Why: Students must understand how to interpret subscripts in chemical formulas to correctly write formulas from names.

Periodic Table and Element Types

Why: Students need to identify metals and nonmetals to distinguish between ionic and covalent compounds, and to understand the basis for covalent nomenclature.

Introduction to Ions and Ionic Nomenclature

Why: Familiarity with naming ionic compounds provides a foundation for understanding the systematic approach to chemical nomenclature and helps differentiate covalent naming rules.

Key Vocabulary

binary covalent compound	A compound formed from two different nonmetal elements, named using prefixes to indicate the number of atoms of each element.
prefix	A syllable added to the beginning of a word, used in covalent nomenclature to denote the quantity of an atom (e.g., di-, tri-, tetra-).
binary acid	An acid composed of hydrogen and one other nonmetal element, named using the 'hydro-___-ic acid' pattern.
oxyacid	An acid containing hydrogen, oxygen, and at least one other element, named based on the polyatomic ion it contains.
suffix	A syllable added to the end of a word, used in acid nomenclature to indicate the type of acid (e.g., -ic, -ous).

Watch Out for These Misconceptions

Common Misconception

Covalent compounds follow the same naming rules as ionic compounds.

What to Teach Instead

Ionic compounds use a metal cation and nonmetal anion; covalent compounds use prefixes because two nonmetals can combine in many ratios. NaCl is always sodium chloride, but N and O can form NO, NO₂, N₂O, and more. Without prefixes, the formula would be ambiguous. Sorting examples by compound type before naming reinforces which rule applies when.

Common Misconception

All compounds containing hydrogen and a nonmetal are acids.

What to Teach Instead

Organic compounds like CH₄ contain hydrogen bonded to carbon but are not Arrhenius acids. Binary acids are specific compounds that dissolve in water to release H⁺ ions. Context , aqueous solution , matters for applying the acid naming convention correctly.

Common Misconception

The 'mono' prefix is always used for the first element in a covalent compound.

What to Teach Instead

By convention, 'mono' is never used for the first element. CO is 'carbon monoxide,' not 'monocarbon monoxide.' Students must apply this exception consistently. Flashcard practice with the specific rule stated explicitly helps address this, as it is easy to apply 'mono' habitually to both elements.

Active Learning Ideas

Flowchart Practice: Naming Decision Tree

Students receive a blank flowchart template with key decision points (covalent compound or acid? contains oxygen?) and fill in the appropriate naming rule at each branch. They apply the completed flowchart to ten compounds, then compare flowcharts with a partner to identify any discrepancies.

25 min·Pairs

Card Sort: Acids vs. Binary Covalent

Students receive sixteen formula cards and sort them into binary covalent compounds, binary acids, and oxyacids. After sorting, pairs name all sixteen compounds, check against an answer key, and note which rule each name follows , building category fluency alongside naming practice.

30 min·Pairs

Error Analysis: Name That Mistake

Students receive ten compound names with deliberate errors , wrong prefix, wrong acid naming pattern, or wrong suffix. They identify and correct each error, writing which specific rule was violated before comparing corrections with a partner.

20 min·Individual

Relay Race: Formula-to-Name Relay

In groups of four, each student names one compound and writes it on the board before passing the marker. The first group to correctly name all four compounds wins. A class-wide discussion follows on any contested names to clarify the rule at stake.

15 min·Small Groups

Real-World Connections

• Chemists in pharmaceutical companies use systematic nomenclature to precisely identify and synthesize new drug compounds, ensuring accurate labeling and safe administration.
• Environmental scientists analyzing air or water samples rely on correct naming conventions to differentiate between various atmospheric pollutants like sulfur dioxide (SO₂) and sulfur trioxide (SO₃), which have different environmental impacts.
• Food scientists use nomenclature to describe ingredients in processed foods, such as carbon dioxide (CO₂) used as a leavening agent or preservative.

Assessment Ideas

Quick Check

Provide students with a list of 5-7 chemical formulas. Ask them to write the correct IUPAC name for each, identifying whether each is a binary covalent compound, binary acid, or oxyacid. For example: CO₂, H₂S, HNO₃.

Exit Ticket

On one side of an index card, write the name 'dinitrogen pentoxide'. On the other side, write the name 'hydrochloric acid'. Ask students to write the corresponding chemical formula for each and briefly explain one rule they used for each naming convention.

Peer Assessment

Students work in pairs. One student writes 3-4 chemical names (mix of covalent and acids) and gives them to their partner. The partner writes the formulas. They then swap papers and check each other's work, identifying any errors and explaining the correct naming rule.

Frequently Asked Questions

When do you use prefixes in chemical nomenclature?

Prefixes are used when naming binary covalent compounds , two nonmetals , to specify exactly how many atoms of each element are present. They are not used for ionic compounds or acid names. This distinction is fundamental: the same formula-to-name rules do not apply across all compound types.

What is the difference between naming a binary acid and naming an oxyacid?

Binary acids (no oxygen) use the pattern 'hydro + root + ic acid' (e.g., hydrochloric acid for HCl(aq)). Oxyacids take their name from the polyatomic ion: -ate ions become '-ic acid' and -ite ions become '-ous acid' (e.g., sulfate → sulfuric acid; sulfite → sulfurous acid). The polyatomic ion name is the key to the oxyacid name.

Why does 'monooxide' get shortened to 'monoxide'?

When a prefix ends in a vowel (mono-, hexa-) and the element name begins with a vowel (oxide, iodide), the extra vowel is dropped for easier pronunciation. So 'mono + oxide' becomes 'monoxide' and 'hexa + oxide' becomes 'hexoxide.' This is a pronunciation convention, not a chemistry rule.

How does using a decision tree help students learn covalent and acid nomenclature?

Decision trees make the underlying logic explicit rather than presenting naming as a list of disconnected rules. Students who build and then apply their own flowcharts retain the rules better than those who work from example lists, because the tree forces them to identify the decision point at each step , building procedural reasoning, not just pattern matching.