Naming Covalent Compounds

Naming Covalent Compounds

High School

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Learning Objectives

• Define a covalent compound and differentiate it from an ionic compound.

• Recall and apply Greek prefixes for numbers 1-10 in naming compounds.

• Apply the rules to correctly name a binary covalent compound from its chemical formula.

• Write the correct chemical formula for a binary covalent compound from its name.

Key Vocabulary

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Covalent Compound

A compound made of two or more nonmetals that are sharing electrons between them.

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Ionic Compound

A compound formed between a metal and a nonmetal through the complete transfer of valence electrons.

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Prefix

A prefix is a word part added to the beginning of a word to change its meaning.

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Binary Covalent

A compound that is formed from exactly two different nonmetal elements sharing electrons.

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Subscript

A number written below and to the right of a chemical symbol showing the number of atoms.

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What is a Covalent Compound?

Ionic Compound

• ​Composed of a metal and a nonmetal that are bonded together.

• ​​Involves the transfer of electrons, resulting in positive and negative charges.

• ​Naming these compounds often involves the use of Roman numerals for clarity.

Covalent Compound

• ​Composed of two nonmetals that are sharing electrons with each other.

• ​​Involves the sharing of electrons, so no positive or negative charges form.

• ​The naming system uses Greek prefixes to indicate the number of each atom.

Multiple Choice

Which of the following statements is true about covalent compounds?

• They are made of ions with positive and negative charges.

• They are formed by two nonmetals sharing electrons and are named using Greek prefixes.

• They involve the transfer of electrons between a metal and a nonmetal.

• They have high melting points and are named using Roman numerals.

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Rules for Naming Covalent Compounds

• Name the first nonmetal; use a prefix, but never use ‘mono-’ on it.

• ​Name the second nonmetal, but be sure to change its name ending to ‘-ide’.

• Add a prefix to the second element, like in dichlorine heptoxide (Cl₂O₇).

• Drop the prefix's vowel if the element name starts with 'o', like monoxide.

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Solved Example 1
What is the chemical formula for dinitrogen tetroxide?

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Step 1: Analyze and Sketch the Problem

• Goal: To write the chemical formula for dinitrogen tetroxide.

• Knowns: The name of the covalent compound is dinitrogen tetroxide. The prefixes tell us the number of atoms of each element.

• Unknowns: The chemical symbols and subscripts for the formula.

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Solved Example 1
What is the chemical formula for dinitrogen tetroxide?

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Step 2: Solve for the Unknown

• "Di-" in dinitrogen means there are 2 atoms of nitrogen (N).

• "Tetr-" in tetroxide means there are 4 atoms of oxygen (O).

• Combine the symbols and subscripts to get the formula: N₂O₄.

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Solved Example 1
What is the chemical formula for dinitrogen tetroxide?

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Step 3: Evaluate the Answer

• The chemical formula is written as N₂O₄.

• This matches the prefixes in the name: N₂ for dinitrogen and O₄ for tetroxide, so the formula is correct.

Multiple Choice

Following the naming rules, what is the correct name for the compound CO?

• Carbon oxide

• Monocarbon monooxide

• Carbon monoxide

• Monocarbon oxide

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How to Write Chemical Formulas

• A prefix on the first element’s name gives its subscript; no prefix means 1.

• A prefix on the second element’s name gives the subscript for its symbol.

• Dinitrogen monoxide (N₂O) has 2 nitrogens ('di-') and 1 oxygen ('mono-').

• Phosphorus trifluoride (PF₃) has 1 phosphorus (no prefix) and 3 fluorines ('tri-').

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Multiple Choice

What is the correct chemical formula for dinitrogen pentachloride?

• N₂Cl

• N₅Cl₂

• N₂Cl₅

• NCl

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Common Misconceptions in Naming Compounds

Misconception	Correction
Prefixes are used for all chemical compounds.	Prefixes are only for covalent compounds, not ionic ones.
The prefix 'mono-' is always used for one atom.	The prefix 'mono-' is never used on the first element.
Covalent compounds have positive or negative charges.	Covalent compounds share electrons and do not have charges.

Multiple Choice

Why is it necessary to use prefixes when naming covalent compounds like CO and CO₂, but not for an ionic compound like NaCl?

• Because nonmetals can form multiple different compounds together, and prefixes specify the exact ratio of atoms.

• Because covalent compounds are always gases and need special names.

• Because ionic compounds don't have subscripts in their formulas.

• Because the periodic table requires prefixes for all elements on the right side.

Multiple Choice

Which of the following pairs of compounds is named correctly according to the rules for covalent compounds?

• PBr₅: Phosphorus pentabromide; CO: Carbon monoxide

• CO₂: Monocarbon dioxide; NCl₂: Nitrogen dichloride

• N₂O₃: Dinitrogen oxide; SO₃: Monosulfur trioxide

• S₅F₄: Sulfur tetrafluoride; NH₃: Nitrogen hydride

Multiple Choice

A compound has the formula As₂Br₃. Based on the naming rules, what is the correct name, and what does the formula tell you about the compound's structure?

• Biarsenic tribromide; it has a high melting point.

• Arsenic (III) bromide; it has a charge of +3 on the arsenic.

• Diarsenic tribromide; it is a molecule with two arsenic atoms and three bromine atoms sharing electrons.

• Arsenic bromide; it is an ionic compound.

Multiple Choice

If you are given the name 'dicarbon trichloride,' what steps would you take to write its chemical formula, and why is it incorrect to name it 'carbon chloride'?

• The name is incorrect, it should be Dicarbon Trichlorine.

• Ignore the prefixes and criss-cross charges (C₃Cl₂); prefixes are just suggestions for covalent compounds.

• Write the symbols C and Cl; the name is sufficient without prefixes because their charges are known.

• Use the prefixes 'di-' for carbon and 'tri-' for chloride to get the subscripts C₂Cl₃; prefixes are essential because they specify the exact ratio of atoms.

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Summary

• Covalent compounds are formed when nonmetals share electrons.

• Use Greek prefixes for atom counts and change the second element's ending to -ide.

• To write a formula, use the prefixes as subscripts for each element.

• Never use 'mono-' on the first element; names must specify the atom ratio.

Poll

On a scale of 1-4, how confident are you about naming and writing formulas for covalent compounds?

• 1

• 2

• 3

• 4