UNIT 1
Chapter 3: Chemical Names, Formulae, & Equations
Unit 1: Chemistry
Chapter 3: Molecular Compounds
Science 10
Mrs. Purba
UNIT 1
Chapter 3: Chemical Names, Formulas, and Equations
Section 3.1
Molecular Compounds
• 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?
UNIT 1
Chapter 3: Chemical Names, Formulas, and Equations
Section 3.2
Nomenclature and Formulae of Binary
Molecular Compounds
• 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.
UNIT 1
Chapter 3: Chemical Names, Formulas, and Equations
Section 3.2
Nomenclature and Formulae of Binary
Molecular Compounds
• 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?
UNIT 1
Chapter 3: Chemical Names, Formulas, and Equations
Section 3.2
Nomenclature and Formulae of Binary
Molecular Compounds
• 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.
UNIT 1
Chapter 3: Chemical Names, Formulas, and Equations
Section 3.2
Rules for Writing Names and Formulas of
Binary Molecular Compounds
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.
UNIT 1
Chapter 3: Chemical Names, Formulas, and Equations
Section 3.2
Rules for Writing Names and Formulas of
Binary Molecular Compounds
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.”
UNIT 1
Chapter 3: Chemical Names, Formulas, and Equations
Section 3.2
Rules for Writing Names and Formulas of
Binary Molecular Compounds
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.
UNIT 1
Chapter 3: Chemical Names, Formulas, and Equations
Section 3.2
Sample Problem:
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?
UNIT 1
Chapter 3: Chemical Names, Formulas, and Equations
Section 3.2
IUPAC and Systematic Names
• 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.
UNIT 1
Chapter 3: Chemical Names, Formulas, and Equations
Key Naming Rules: A Summary
Section 3.2
UNIT 1
Chapter 3: Chemical Names, Formulas, and Equations
Section 3.2
Exceptions to the Rules
• 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.
HCl
If hydrogen chloride was
named according to the
naming rules for molecular
compounds, it would be
called hydrogen
monochloride.
UNIT 1
Chapter 3: Chemical Names, Formulas, and Equations
Section 3.2
Section 3.2 Review
• 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).