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8.1 Molecular Compounds > Molecules and
8.1 Molecular Compounds >
Molecular Compounds
Molecules and Molecular Compounds
Chapter 8
Covalent Bonding
What information does a molecular
formula provide?
8.1 Molecular Compounds
8.2 The Nature of Covalent Bonding
8.3 Bonding Theories
8.4 Polar Bonds and Molecules
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8.1 Molecular Compounds > Molecules and
Molecular Compounds
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8.1 Molecular Compounds > Molecules and
Molecular Compounds
In nature, only the noble gas elements, such
as helium and neon, exist as uncombined
atoms.
But not all elements are monatomic.
•  O2 represents two oxygen
atoms that are bonded
together.
•  Monatomic molecules
•  What are the 7 diatomic
molecules?
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8.1 Molecular Compounds > Molecules and
Molecular Compounds
8.1 Molecular Compounds > Molecules and
Molecular Compounds
Ionic compounds are generally crystalline solids
with high melting points.
The attractions that hold together the
atoms in O2, H2O, CO2, and N2O are not
ionic bonds.
Molecular compounds, however, have very
different properties.
•  do not involve the transfer of electrons.
•  Water (H2O) is a liquid at
room temperature.
•  Carbon dioxide (CO2) and
nitrous oxide (N2O) are
both gases at room
temperature.
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8.1 Molecular Compounds > Molecules and
Molecular Compounds
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8.1 Molecular Compounds > Molecules and
Molecular Compounds
Sharing Electrons
•  Molecular compounds combine by
sharing electrons.
Sharing Electrons
A molecule is a neutral group of atoms
joined together by covalent bonds.
–  covalent bond
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•  Oxygen gas consists of oxygen molecules;
each oxygen molecule consists of two
covalently bonded oxygen atoms.
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8.1 Molecular Compounds > Molecules and
Molecular Compounds
8.1 Molecular Compounds > Molecules and
Molecular Compounds
Representing Molecules
•  A molecular formula shows how many
atoms of each element a substance
contains.
Representing Molecules
The molecular formula of water is H2O.
•  The subscript after an element’s symbol
indicates the number of atoms of each
element in the molecule.
•  the subscript 1 is omitted.
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8.1 Molecular Compounds > Molecules and
Molecular Compounds
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8.1 Molecular Compounds > Molecules and
Molecular Compounds
Representing Molecules
Butane is also a molecular compound.
Representing Molecules
A molecular formula reflects the actual
number of atoms in each molecule.
•  The molecular formula
for butane is C4H10.
•  The subscripts are not necessarily the
lowest whole-number ratios.
•  One molecule of
butane contains four
carbon atoms and ten
hydrogen atoms.
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8.1 Molecular Compounds > Molecules and
Molecular Compounds
8.1 Molecular Compounds > Molecules and
Molecular Compounds
Representing Molecules
A molecular formula does not tell you
about a molecule’s structure.
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8.1 Molecular Compounds > Molecules and
8.1 Molecular Compounds > Molecules and
Representing Molecules
Representing Molecules
The arrangement of atoms within a
molecule is called its molecular structure.
Molecular Compounds
The arrangement of atoms within a
molecule is called its molecular structure.
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Molecular Compounds
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8.1 Molecular Compounds > Molecules and
Molecular Compounds
8.1 Molecular Compounds >
Representing Molecules
The arrangement of atoms within a
molecule is called its molecular structure.
Acetylsalicylic acid, also known as aspirin,
has a molecular formula of C9H8O4.
What elements make up acetylsalicylic acid?
How many atoms of each element are found
in one molecule of acetylsalicylic acid?
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8.1 Molecular Compounds > Comparing Molecular and
Ionic Compounds
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8.1 Molecular Compounds > Comparing Molecular and
Ionic Compounds
Comparing Molecular and Ionic
Compounds
The representative unit of a molecular
compound is a molecule.
For an ionic compound, the smallest
representative unit is a formula unit.
What representative units define
molecular compounds and ionic
compounds?
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8.1 Molecular Compounds > Comparing Molecular and
Ionic Compounds
8.1 Molecular Compounds > Comparing Molecular and
Ionic Compounds
•  Recall that a formula unit is the lowest wholenumber ratio of ions in an ionic compound.
Molecular compounds tend to have
relatively lower melting and boiling points
than ionic compounds.
–  A molecule is made up of two or more
atoms that act as a unit.
•  So, Many molecular compounds are gases or
liquids at room temperature.
–  No such units exist in an ionic compound
–  continuous array of ions
–  There is no such thing as a molecule of
sodium chloride or magnesium chloride.
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8.1 Molecular Compounds > Comparing Molecular and
Ionic Compounds
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8.1 Molecular Compounds > Comparing Molecular and
Ionic Compounds
•  Ionic compounds
Collection of
water molecules
Array of
sodium ions and
chloride ions in a
crystal
1 Molecule of
Water made up of 3
atoms
Formula unit of
sodium chloride
made up of 2 ions
•  formed from a metal combined with a
nonmetal
•  Higher melting points and boiling points
•  Solids at room temperature
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Chemical formula
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H 2O
NaCl
Chemical formula
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8.1 Molecular Compounds >
How is the formula unit of an ionic
compound different from a
molecule?
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