I. Molecular Compounds
In a covalent bond atoms are held
together by sharing electrons.
 A molecule is a neutral group of atoms
joined together by covalent bonds.
 A compound composed of molecules is
called a molecular compound.

 The molecules of a given compound are all
the same.
II. Molecular Formulas
A molecular formula shows how many
atoms of each element a molecule
contains.
 The molecular formula does not tell you
about a molecule’s structure.

Ionic Compounds
--Cation (Metal loses
electron(s)
--Anion (Non-metal gains
electron(s)
Examples:

Which of the following are covalent
compounds?
 NaBr
 SiO2
 CO2
 AlCl3
 CH4
III. Molecular Compound
Properties

Molecular cpds tend to have relatively
lower melting and boiling points than
ionic cpds.
 Many molecular cpds are gases or liquids at
RT.
Properties Table
IONIC
COVALENT
Bond
Formation
e- are transferred from
metal to nonmetal
e- are shared between
two nonmetals
Type of
Structure
crystal lattice
true molecules
Physical
State
solid
liquid or gas
Melting
Point
high
low
Solubility in
Water
yes
usually not
Electrical
Conductivity
yes
(solution or liquid)
Form electrolytes in
solution
Other
Properties
no
odorous
IV. Bond Polarity

Most bonds are a
blend of ionic and
covalent
characteristics

Difference in
electronegativity
determines bond
type
IV. Bond Polarity

Electronegativity – Remember this?
 Attraction an atom has for a shared pair of
electrons
 higher e-neg atom   lower e-neg atom +
IV. Bond Polarity

Electronegativity Trend
 Increases up and to the right.
IV. Bond Polarity

Nonpolar Covalent Bond
 e- are shared equally
 usually identical atoms
IV. Bond Polarity

Polar Covalent Bond
 e- are shared unequally
 results in partial charges
+


IV. Bond Polarity
z Nonpolar
z Polar
z Ionic
View Bonding Animations.
IV. Bond Polarity
Examples:

Cl2

HCl 3.16-2.20=0.96
3.16-3.16=0.0
Nonpolar
Polar

NaCl
3.16-0.93=2.23
Ionic
V. Octet Rule in Covalent bonding
In covalent bonds, electron sharing
usually occurs so that atoms attain the
electron configuration of noble gases.
 Combinations of atoms of the nonmetals
and metalloids in groups 14-17 of the
periodic table are likely to form covalent
bonds.

VI. Single Covalent Bonds

Two atoms held together by a sharing a
pair of electrons are joined together by a
single covalent bond.
VI. Single Covalent Bonds

An electron dot structure represents the
shared pair of electrons of the covalent
bond by two dots.

A structural formula represents the
covalent bonds by dashes and shows the
arrangement of covalently bonded atoms
IV. Single Covalent Bonds

A pair of valence electrons that is not
shared between atoms is called an
unshared pair, also known as a lone pair
of a nonbonding pair.
Lone pair
VII. Double and Triple Covalent
Bonds
Atoms form double or triple covalent
bonds if they can attain a noble gas
structure by sharing two or three pairs of
electrons.
 A double bond involves sharing two
pairs of electrons.
 A triple bond involves sharing three pairs
of electrons.

VII. Double and Triple Covalent
Bonds
Lewis Structures
Predict the location of certain atoms
2. Determine the number of electrons
available for bonding
3. Place bonds to form the skeletal
structure
4. Determine the number of valence
electrons remaining
5. Determine whether the central atom
satisfies the octet rule
1.
Lewis Structures

The chemical symbol for the element is
surrounded by a number of dots
corresponding to number of valence
electrons
X. Lewis Structures for Covalent
Compounds
In a covalent compound, electrons are
shared between atoms to form a covalent
bond in order that each atom in the
compound has a share in the number of
electrons required to provide a stable,
Noble Gas, electronic configuration.
 Electrons in the Lewis Structure (electron
dot diagram) are paired to show the
bonding pair of electrons. Katie loves mrs
chilton!

X. Lewis Structures for Molecular
Compounds

Carbon fluoride
 CF4
+ 4
=
Lewis Structures for Ionic
Compounds
The overall charge on the compound
must equal zero, that is, the number of
electrons lost by one atom must equal
the number of electrons gained by the
other atom.
 The Lewis Structure (electron dot
diagram) of each ion is used to construct
the Lewis Structure (electron dot
diagram) for the ionic compound.

X. Lewis Structures for Ionic
Compounds
Practice!

Sulfur trioixide

Boron trifluoride

Carbonate
XI. Resonance

A resonance structure is a structure that
occurs when it is possible to draw two or
more valid electron dot structures (Lewis
structures) that have the same number
of electron pairs for a molecule or ion.