Unit 1: Chemistry

Chapter 3: Molecular Compounds

Science 10

Mrs. Purba

UNIT 1 Chapter 3: Chemical Names, Formulae, & Equations

Molecular Compounds

UNIT 1 Chapter 3: Chemical Names, Formulas, and Equations Section 3.1

• A molecule is a particle formed by two or more atoms

joined by covalent bonds.

• A molecular compound is a compound formed of atoms of

two or more elements that share electrons.

• The particles in a molecule are held together by covalent

bonds.

• What properties do molecular

compounds usually have?

• What role do electrons have

in covalent bonds?

Nomenclature and Formulae of Binary

Molecular Compounds

UNIT 1 Chapter 3: Chemical Names, Formulas, and Equations Section 3.2

• A binary molecular compound is a compound composed of

atoms of two different elements, usually two non-metals,

that are joined together with covalent bonds.

Nomenclature and Formulae of Binary

Molecular Compounds

UNIT 1 Chapter 3: Chemical Names, Formulas, and Equations Section 3.2

• Chemical formulas of binary molecular compounds

indicate how many atoms of each element are present in a

single molecule of the compound, as shown for sulfur

hexafluoride.

• What is the name of a binary

molecular compound that contains

one sulfur atom and six fluorine atoms?

Nomenclature and Formulae of Binary

Molecular Compounds

UNIT 1 Chapter 3: Chemical Names, Formulas, and Equations Section 3.2

• Like the names for ionic compounds, names for binary

molecular compounds have only two “parts” to consider.

• The following three rules will help you write names and

formulas of binary molecular compounds.

Rules for Writing Names and Formulas of

Binary Molecular Compounds

UNIT 1 Chapter 3: Chemical Names, Formulas, and Equations Section 3.2

1. The first element in the name and formula of a binary

molecular compound is usually the one that is farther to

the left on the periodic table.

Example: In carbon monoxide, CO, carbon comes first

because carbon is to the left of oxygen on the

periodic table.

Rules for Writing Names and Formulas of

Binary Molecular Compounds

UNIT 1 Chapter 3: Chemical Names, Formulas, and Equations Section 3.2

2. When naming, the suffix “–ide” is attached to the name of

the second element.

Example: “Oxygen” is changed to “oxide” in the name

“carbon monoxide.”

Rules for Writing Names and Formulas of

Binary Molecular Compounds

UNIT 1 Chapter 3: Chemical Names, Formulas, and Equations Section 3.2

3. When naming, prefixes are used to indicate how many

atoms of each type are present in one molecule of the

compound.

• The prefix “mono-” is used only for the second element in

the name.

• Also, when “mono-” comes before “-oxide,” an "o" is

dropped. Thus, you write “monoxide,” not “monooxide.”

Example : Using prefixes correctly, the name of CO is carbon

monoxide.

Sample Problem:

UNIT 1 Chapter 3: Chemical Names, Formulas, and Equations Section 3.2

Nitrogen and oxygen form a wide variety of different

molecular compounds with different properties. Two

examples are described below.

(a) Dinitrogen tetraoxide is used in rocket fuels. What is its

formula?

(b) NO2 is a toxic brown gas that is found in smog in urban

areas. What is its name?

Problem

• The compound NO acts to widen blood

vessels, which can lessen chest pain in

heart patients.

• The patient takes nitroglycerin pills,

which react in the body to form NO.

• What is the name of the

compound NO?

IUPAC and Systematic Names

UNIT 1 Chapter 3: Chemical Names, Formulas, and Equations Section 3.2

• The international system for naming chemicals is

maintained by the International Union of Pure and Applied

Chemistry (IUPAC).

• IUPAC has developed a systematic method for naming

chemicals according to their composition.

• Why is an international system for

naming chemicals important?

These calcium sulfate crystals are found in Mexico.

Thanks to IUPAC, scientists around the world can

share information about them.

Key Naming Rules: A Summary

UNIT 1 Chapter 3: Chemical Names, Formulas, and Equations Section 3.2

Exceptions to the Rules

UNIT 1 Chapter 3: Chemical Names, Formulas, and Equations Section 3.2

• Compounds that contain hydrogen are exceptions to the

general naming rules. Hydrogen is a non-metal, and

hydrogen chloride (HCl) is molecular compound. Binary

hydrogen compounds are named as though they are ionic

compounds.

• Compounds that contain hydrogen and carbon are also

named differently.If hydrogen chloride was

named according to the

naming rules for molecular

compounds, it would be

called hydrogen

monochloride.

HCl

Section 3.2 Review

UNIT 1 Chapter 3: Chemical Names, Formulas, and Equations Section 3.2

• Chemical compounds are named according to whether

they are ionic or molecular.

• The formula of an ionic compound represents the ratio of

the positive and negative ions in the electrically neutral

compound.

• The formula of a molecular compound represents the

number of atoms of each element in a molecule of the

compound.

• Chemical names and formulas are standardized by bodies

such as the International Union of Pure and Applied

Chemistry (IUPAC).