Why do Covalent Compounds have
Low Conductivity?
• Have a wider variety of properties than ionic
compounds
• Atoms are held together with strong covalent
bonds (<0.5)
• Bonds do NOT break
• Covalent compounds are also called molecular
compounds
Evidence for Intermolecular Forces
• The forces that bond the atoms to each other
within a molecule are called intramolecular
forces.
• Covalent bonds are intramolecular forces
• The forces that bond molecules together are
called intermolecular forces.
Look at the difference between these two types of forces. Pure
covalent compounds have low melting and boiling points, you
know that the intermolecular forces must be very weak in
comparison to the intramolecular forces or covalent bonds. It
does not take very much energy to break the bonds that hold the
molecules to each other.
Polar Bonds and Molecular Shape
Other examples of polar molecules
(asymmetrical)
Non- Polar Molecules
Carbon Dioxide
Bonds: DEN = 1 = so Polar Covalent BOND
BUT, is the whole molecule polar??
No!,
The molecule is straight and symmetrical
meaning that the effects of polar bonds cancel
each other out
So, although the BONDS are POLAR, the
molecule is NON-POLAR
Other examples of Non-Polar
molecules
• CF4
• CH4
• Remember inter-intra molecular forces?
• Non-polars have relatively weak intermolecular
forces, so their melting points are lower than
polar molecules.
• Eg. CO2 is a gas at room temp, Melting point is 57 degrees.
Other Properties
• Polar: +/- ends means that the molecule will
easily “stick” to itself = High melting point and
boiling point
• Non-Polar: do not attract each other as much
due to not having +/- poles = low melting and
boiling points.
• Non-polar compounds are often gases at room
temperature.
Concept Organizer pp.93
• Make sure to do your homework questions
• Let’s investigate further in respect to
molecular shape
• Lesson #4 in the green book.