Bellringer #lewis #bonding
• What type of bonds do these elements
form?
• NaF, KI, CO2, HF, CCl4, H2O, CaCl2
• Draw the Lewis Bonding Structures for:
CCl3OH, SiS2, N2, N2F2
Electronegativity
What is it?
• Electronegativity is the power of an
atom to attract electron density 
in a covalent bond 
Remember the definition …
… look for where you get the ticks!
Electronegativity
Pauling’s electronegativity scale
• The higher the value, the more
electronegative the element
• Fluorine is the most electronegative element
• It has an electronegativity value of 4.0
Electronegativity
Pauling’s electronegativity scale
Electronegativity
Pauling’s electronegativity scale
H
2.1
He
-
Li
1.0
Be
1.5
B
2.0
C
2.5
N
3.0
O
3.5
F
4.0
Ne
-
Na
0.9
Mg
1.2
Al
1.5
Si
1.8
P
2.1
S
2.5
Cl
3.0
Ar
-
Chemical Bonding and
VSEPR
•6
The Shapes of Molecules
• The shape of a molecule has an important
bearing on its reactivity and behavior.
• The shape of a molecule depends a
number of factors. These include:
1. Atoms forming the bonds
2. Bond distance
3. Bond angles
•7
Valence Shell Electron Pair
Repulsion
• Valence Shell Electron Pair Repulsion
(VSEPR) theory can be used to predict the
geometric shapes of molecules.
• VSEPR is revolves around the principle
that electrons repel each other.
• One can predict the shape of a molecule
by finding a pattern where electron pairs
are as far from each other as possible.
•8
Bonding Electrons and Lone
Pairs
• In a molecule some of the
valence electrons are shared
between atoms to form
covalent bonds. These are
called bonding electrons.
• Other valence electrons may
not be shared with other
atoms. These are called
non-bonding electrons or
they are often referred to as
lone pairs.
•9
VSEPR
• In all covalent molecules
electrons will tend to stay as far
away from each other as
possible
• The shape of a molecule
therefore depends on:
1. the number of regions of
electron density it has on its
central atom,
2. whether these are bonding
or non-bonding electrons.
•10
Lewis Dot Structures
• Lewis Dot structures are used
to represent the valence
electrons of atoms in covalent
molecules
• Dots are used to represent
only the valence electrons.
• Dots are written between
symbols to represent bonding
electrons
•11
Violations of the Octet Rule
Violations of the octet rule usually
occur with B and elements of higher
periods. Some common examples
include: Be, B, P, S, and Xe.
•Be: 4
•B:
•BF3
6
•P:
8 OR 10
•S:
8, 10, OR
12
•SF4
VSEPR Predicting Shapes
VSEPR: Predicting the shape
•
Once the dot structure has been
established, the shape of the molecule
will follow one of basic shapes depending
on:
1. The number of regions of electron density
around the central atom
2. The number of regions of electron density
that are occupied by bonding electrons
•14
VSEPR: Predicting the shape
•
•
The number of regions of electron
density around the central atom
determines the electron structure
The number of regions of electron
density that are occupied by bonding
electrons and hence other atoms
determines the actual molecular shape
•15
Basic Molecular shapes
The most
common
shapes of
molecules are
shown at the
right
•16
Linear Molecules
Linear molecules
have only two
regions of
electron density.
•17
Angular or Bent
Angular or bent
molecules have
at least 3 regions
of electron
density, but only
two are occupied
•18
Triangular Plane
Triangular planar
molecules have
three regions of
electron density.
All are occupied by
other atoms
•19
Tetrahedron
Tetrahedral
molecules have
four regions of
electron density.
All are occupied
by other atoms
•20
Trigonal Bipyramid
A few molecules
have expanded
valence shells
around the central
atom. Hence there
are five pairs of
valence electrons.
The structure of
such molecules
with five pairs
around one is
called trigonal
bipyramid.
•21
Octahedron
A few molecules
have valence shells
around the central
atom that are
expanded to as
many as six pairs or
twelve electrons.
These shapes are
known as
octahedrons
•22
Molecular Polarity
Molecular Polarity depends on:
1. the relative electronegativities of the
atoms in the molecule
2. The shape of the molecule
3. Molecules that have symmetrical charge
distributions are usually non-polar
•23
Non-polar Molecules
•The electron density plot for H2.
• Two identical atoms do not have an
electronegativity difference The charge
distribution is symmetrical.
• The molecule is non-polar.
•24
Polar Molecules
•The electron density plot for
HCl
•
•
•
•
Chlorine is more electronegative than Hydrogen
The electron cloud is distorted toward Chlorine
The unsymmetrical cloud has a dipole moment
HCl is a polar molecule.
•25
Molecular Polarity
To be polar a molecule must:
1. have polar bonds
2. have the polar bonds
arranged in such a way
that their polarity is not
cancelled out
3. When the charge
distribution is nonsymmetrical, the
electrons are pulled to
one side of the molecule
4. The molecule is said to
have a dipole moment.
• HF and H2O are both polar
molecules. CCl4 is non-polar
•26
Don’t Forget
• Chapter 8 HW packet
due Thursday and
Friday of this week!