Bonding in Covalent
Compounds
Stable Atoms
Stable Atoms

Have low chemical reactivity

Include noble gases which all have full valence
energy levels (duet for helium, octet for the rest!)

Other atoms become stable by changing the # e- to
have an electron configuration like the nearest noble
gas
a) Octet rule – change to have 8 valence e- Most atoms!
b) Duet rule – change to have 2 valence e- includes H, Li, and Be

Covalent bonding and Ionic Bonding allow atoms to
gain a stable e- configuration.
Covalent (Molecular) Bonding

Covalent bonds: bonds that result from the sharing of
valence electrons between atoms.

Occurs only between non-metal atoms within a molecule.

By sharing electrons, each atom obtains a stable electron
configuration.

Can be single, double, or triple covalent bonds

Examples: H2
H2 O
Lewis Diagrams for Molecules
Rules:
1) Draw the L.D. for each of the atoms in the molecule.
2)
Unpaired e- (bonding e-) are available to form a covalent
bond. Any e- in lone pairs are not used in bonding.
3)
The atom with the most bonding e- (Central atom) is
placed in the centre with other atoms bonded to it.
4)
Compound L.D. must have all e- in pairs with each atom
(except H) surrounded by an octet of e-.
Examples: HF
NH3
Worksheet 2, #’s 1-8
Lewis Diagrams with Multiple Bonds

Atoms that have two or more bonding e- may share
more than one e- in a bond with another atom
2
e- pairs shared between 2 atoms = double bond
 3 e- pairs shared between 2 atoms = triple bond
Examples:
a) O2 Oxygen
b) N2 Nitrogen
c) C2H4 Ethene
d) C2F2 Difluoroethyne
Structural Formulas for Molecules

A structural formula shows how the atoms are
connected in a molecule

To draw a structural formula:
 Replace
each pair of bonded electrons with a short
line.
 Omit the lone pairs of electrons.
Examples:
a) C2H4
b) NH3
Stereochemistry - VSEPR Theory
Stereochemistry - VSEPR Theory

Stereochemistry: the study of the shape of
chemical species (compounds)
 VSEPR
stands for “valence shell electron
pair repulsion”
 It
allows us to predict and draw 3D shapes
of molecules from Lewis diagrams.
Rules for VSEPR Theory
1.
Valence e- pairs (lone and bonding) are
arranged around the central atom of a
molecule so as to minimize repulsion.
2.
When determining shapes of molecules,
treat multiple bonds as single bonds. (only
bond direction matters)
Rules for VSEPR Theory
3. Use the following when drawing 3D shapes:
atom is in same plane as central atom
atom goes behind the plane (away from
you)
atom goes in front of plane (towards you)
Main VSEPR Shapes
1.
2.
3.
4.
5.
Tetrahedral
Pyramidal
V-shaped (bent)
Trigonal Planar
Linear
http://www.pbslearningmedia.org/resource/lsps07.sci.
phys.matter.molecularshp/molecular-shapes/
More on Covalent bonding in the future!