Journal Entry: December 13
1. Determine the molecular geometry of PCl3.
2. Are the P–Cl bonds in PCl3 polar or nonpolar?
Explain the reasoning of your choice.
Use the Modeling kits to build all 5 base shapes
• The central ball is important
– Make sure it has the appropriate number and
spacing of holes
– Go over the 5 base shapes’ names and
angles
• Show me your collection when you’re
done
– Remove one atom at a time and name the
shapes and angles as a team
• Draw the lewis structures, name the
shapes, identify the bond angles for:
– SOF4
– Bromate
– SiO2
Dipoles and Molecular Polarity
• Covalent bonds can be classified as either polar or
nonpolar.
– Polar bonds are created when there is an unequal sharing of
bonded electrons occurring between two atoms (this is due
to differences in electronegativity)
– Nonpolar bonds are created when there is equal sharing of
electrons (same atom, or very small difference in EN like
carbon and hydrogen)
• Molecules as a whole can also be classified as either
polar or nonpolar.
• This affects many of the properties of the substance
such as boiling point and melting point.
Polar Molecules
• Polar molecules are created when the center of
partial positive charge does not coincide with the
center of partial negative charge.
• Example: HCl
• Polar molecules are often called dipoles.
• A dipole is created when the center of partial
positive charge and the center of partial negative
charge are separated by a short distance.
• For molecules that contain more than one bond,
polar molecules are created when the polar bonds
are asymmetrically arranged.
• Example: H2O
• Molecule has a bent shape.
• The molecule has two distinct regions of charge.
• Therefore, water is considered a polar molecule.
• Polarity of Water Video Clip
Nonpolar Molecules
• Molecules with polar bonds do not always create
polar molecules.
• Example: CCl4
• Shape is tetrahedral.
• This time the centers of positive charge and
negative charge coincide.
• This has the net effect of cancelling each other.
• CCl4 is a nonpolar molecule.
• Whenever polar bonds are symmetrically
arranged, they produce nonpolar molecules.
• Another example: CO2
Molecular Polarity and Molecular Geometry
• The shape of the molecule determines how the
bonds are distributed in the molecule.
• The following geometries give asymmetrical
arrangements and produce polar molecules:
– Trigonal pyramidal and bent (Linear if the molecule
only contains two atoms)
• The following geometries give symmetrical
arrangements and produce nonpolar molecules:
– Linear, trigonal planar, and tetrahedral.
What Do You Think?
• CHCl3 is commonly known as chloroform. Would
this molecule be considered polar or nonpolar?
Explain the reasoning of your choice.
• Just remember “SNAP”
– SNAP
Symmetrical Nonpolar Asymmetrical Polar
• Molecular polarity is determined by the shape and
distribution of charge in the molecule. To make your
life easier, just look the atoms.
• If the atoms in the molecule are symmetrical, the
charges are balanced by each other. The
molecules are considered to be nonpolar.
• However, if the molecule is asymmetrical, it is
considered to be polar.
• So if it is lopsided, it is polar. If it is
balanced, it is nonpolar.
Intermolecular Forces
• The negative region in one polar molecule attracts
the positive region in adjacent molecules. So the
molecules all attract each other from opposite sides.
• The forces of attraction between molecules are
known as intermolecular forces.
Wrapping It Up
• Reflect on what you have learned concerning the day’s
topic.
• Respond to the following…
– What are the three most important things you learned
today?
– What is one question you would still like answered?
– What is the one way what you have learned connects with
what you knew before?