>> host: Welcome to
the fourth video
in the Unit 12 playlist of
our "Chemistry Matters" series.
In this video,
we'll provide a quick recap
of the content covered
in Unit 4, Chemical Bonds.
In addition to a fascinating
demonstration where we learned
how to clean pennies
with taco sauce,
In Unit 4 we also learned
how to examine scientific
misconceptions and address them
based on evidence.
For example, we learned
that atoms do not want
or need electrons,
but atoms do attract
or repel electrons
due to electrostatic forces.
In fact, those characteristics
align with the definition
of a chemical bond, which is:
We explored
intramolecular bonds,
which are bonds that hold atoms
together within a molecule
or formula unit.
Rather than bonding simply
being ionic or covalent,
we found that there's
a whole range
of bonding patterns,
referred to as the
Intramolecular Bond Spectrum.
These bonds range from ionic,
to polar covalent,
mostly covalent
and nonpolar covalent.
When we investigated
this bond spectrum,
we found that
electronegativity differences
were the primary
determinant of bond type.
Our students used
a computer simulation
during their performance
task assignment
to investigate the amount of
electronegativity differences
needed for the various types
of intramolecular bonds
to form.
We learned that covalent bonds
occur when one, two or three
electron pairs are shared
between atoms.
Electron pairs are shared
between two atoms
forming single, double
or triple bonds.
Molecules can be binary,
which means composed of
two molecules, or ternary,
which means composed of
three atoms.
Even larger molecules
can form, of course.
Intermolecular forces
between one molecule
and another are weaker
than intramolecular forces.
We saw that cohesion
between water molecules
produces a layer
of surface tension.
Water has rather strong
adhesion properties,
causing water to stick
to all kinds of materials,
making them wet.
We found that alcohol
doesn't have the same
surface tension
because it doesn't have
the same intermolecular forces
as water.
Since alcohol has weaker
intermolecular forces,
it also evaporates
much more easily than water.
In the fifth video
on the Unit 4 playlist,
our students conducted
a jigsaw activity to explore
the properties of the four
main types of intermolecular
forces, listed here
from weakest to strongest:
Dispersion London forces,
Ion-dipole forces,
Dipole-dipole forces,
and hydrogen bonding.
We also conducted a lab
comparing the melting
temperature of a covalently
bonded compound, sugar,
to the melting temperature of
an ionically bonded compound,
sodium chloride.
Our students found
that sugar melted easily,
as intermolecular bonds
were broken by heat.
But an ionic compound,
such as salt, did not melt
easily at all, because
the intramolecular bonds
holding it together
are much stronger.
To help summarize
all of these ideas
and confirm our understanding
of why chemical bonding
is so important,
we invited Dr. Pete Ludovice,
a chemical engineer
at Georgia Tech,
to explain how chemical bonding
affects the properties
of materials.
And join us for the next video
on the Unit 12 playlist,
our recap of Unit 5:
Chemical Reactions.