SCH 4C
Polar Bonds and Polar Molecules
When two atoms with very similar electronegativities bond covalently, the electrons are shared equally by
the two atoms.
This is called a ______________________________.
Two atoms with different electronegativities can still share electrons, but in this case the sharing does not
have to be equal.
δ- means _______________
δ+ means _______________
When an electron pair is not shared equally, there is a buildup of negative charge around one atom,
while the other atom remains more positively charged.
Ions are not created, however!
The electrons are more attracted to the atom with the _____________________.
Using Electronegativities to Predict Bond Type
EN
The difference in electronegativity between two atoms is used to determine whether a bond is covalent,
polar covalent, or ionic.
Predict the type of bond that would be made between the following atoms:
a) Li and F
b) Cl and Br
c) H and O
Polarity in Molecules
If a covalent molecule has polar bonds, it may result in a _______ __________.
Two things must be considered:
1) the presence of _______________ covalent bonds.
2) The _______________________________ (geometry) of the molecule.
Non-polar molecules are very symmetrical and do not have charge differences within the molecule.
Polar molecules have charge differences due to their less perfect geometries.
Symmetry in Molecules
Molecular symmetry can be determined by looking at where electron pairs are placed around a central
atom.
An electron pair can be either a ______________________ pair of electrons or a __________________
pair of electrons.
If all of the electron areas around the central atom are the same, then the molecule has
_______________________.
Examples:
N2
NO2
NH3
CO2
Activity:
Build the following molecules with the molecular modeling kits. Complete the chart below by determining
the bond type, drawing a formal Lewis structure diagram, sketch the shape of the molecule when you
build it, determine if the molecule has symmetry and decide if the molecule is polar or non-polar.
Molecule
O2
CO2
H2O
CH4
H2
HCl
C2H2
CCl4
𝝙EN and
bond type
Lewis Structure
Sketch of
Shape
Symmetry
Molecular
Polarity
Properties of Polar Molecules
Polar molecules can make ________________ _________ which allow like molecules to attract each
other in large numbers.
This is why polar substances tend to have higher melting points and boiling points than non-polar
molecules.
intermolecular bonds
Homework:
1. Which of the following molecules are polar molecules?
F2
H2
O2
H2S
CO2
2. Identify the more polar bond in each of the following pairs.
a) H-F and H-Cl
b) N-O and C-O
c) S-H and O-H
d) P-Cl and S-Cl
e) C-H and N-H
f) S-O and P-O
3. How do intermolecular bonds help to explain why the boiling point of methane, CH4, is much lower
than the boiling point of hydrogen bromide, HBr?