This power point presentation is on
COVALENT BONDING and INTERMOLECULAR FORCES
It covers most of chapter 16
Please take notes as you go, but
there is some good news at the end
for you.
This involves the sharing of
electrons by 2 or more atoms.
The electrons are shared, not
taken as with ionic bonds.
EXAMPLES INCLUDE THE
BONDS BETWEEN:
H2
F2
Br2
Cl2
HCl
H2O
Ionic bonds ONLY happen with
cations and anions that are
metals and non-metals.
All compounds that you just saw are
made with non-metals only.
In a chlorine molecule, each of the atoms
shares a pair of electrons circled in
GREEN, making the covalent bond.
Since it’s just one pair being shared, this is
a SINGLE COVALENT BOND.
Each of the chlorine atoms also has three
pairs each of UNSHARED ELECTRONS.
THEY BOTH GET AN OCTET BY SHARING.
When electrons are written into the Lewis
diagrams, they are usually paired. The
electrons prefer pairs. When they share
themselves with other atoms, one electron
from each atom connects together, making a
SINGLE BOND.
Electrons not involved in bonding are
mostly paired away from the bond. They are
the “unshared” electrons.
If they connect 2 or 3 pairs at a time,
they make DOUBLE or TRIPLE BONDS.
Water has two hydrogen
atoms bonded to one
oxygen atom. It has 2
single polar covalent
bonds.
The oxygen has 2 pairs
of unshared electrons
as well. Oxygen gets
the octet.
NH3 has three single polar covalent bonds,
and nitrogen has one unpaired set of
electrons. N gets the octet.
Nitrogen’s electrons are RED and the
Hydrogen electrons are in BLUE.
there are 2 red, unshared electrons of nitrogen down here
Methane has FOUR single polar covalent bonds,
and that leaves the carbon atom without any
unshared pairs of electrons.
But that’s okay, as long as the electrons are either
paired up or being shared, they are well taken care
of and the molecule is okay.
When 2 oxygen atoms combine to
form a molecule, each keeps two pairs
of unshared electrons, but shares two
pairs (in the middle) with each other.
That is a DOUBLE NON POLAR
COVALENT BOND
Diatomic Nitrogen makes a
TRIPLE COVALENT BOND
and each atom has
one pair of UNSHARED
ELECTRONS.
Polar bonds happen when ever atoms with large
electro-negativity differences connect. The
electrons are not shared evenly, they get taken
by the anion.
Ionic bonds happen when polar bonds are made
between a non-metal and a metal.
Ionic bonds are always polar by definition. Polar
bonds are not always ionic.
This is the SULFITE (–2)
ion
By gaining 2 electrons all
together, sulfur as well as
the three oxygen atoms end
up with a complete octet.
This poly atomic ion acts as
a negative two unit.
Sometimes in these Lewis dot diagrams, we use
dots as well as X’s. The X’s just indicate
electrons from the “other” atoms or ions.
If we used just dots you might get confused
as to where all those electrons came from or
belong.
Bonds can be polar or non-polar.
If a bond is non-polar, that means that there is not a
taking of electrons, making for a positive side and a
negative side of the bond.
If a bond is polar, that means that the electrons are not
shared equally, making one side of the bond more
negative (where the electrons end up) and the other side
more positive (where the electrons were).
HCl is a polar covalent bond.
Your first guess might be that it’s ionic, but
it’s not.
Ionic bonds are ONLY between metals and
non-metals. Hydrogen and chlorine are both
non-metals.
Water also has polar covalent bonds between
the H and the O.
The oxygen is very attracted to the electrons
of hydrogen, so they take them away, making
an octet. The hydrogen side of the molecule
ends up more positive while the oxygen side
is more negative.
a molecule can also be polar, if the electrons are moved
about by polar bonds giving the WHOLE MOLECULE a
positive and a negative side.
The opposite sides of polarity are called dipoles,
which means 2 poles, the positive and the negative side.
The oxygen side is negative
since it takes the electrons,
the hydrogen side is more
positive because it lost the
electrons.
are formed when 2 atoms with different
electro-negativities
form a covalent bond.
The atoms DO NOT SHARE electrons
equally.
The electrons are more strongly
attracted to the MOST electronegative
atom.
see table S for electronegativity
values)
Sort of like, but not really like these love birds,
molecules can also be attracted to each other.
Different forces make them stick together. Love is
not one of these forces, but love is wonderful.
I thought that this was a nice picture to use anyway.
… there are 2 kinds of weak forces that keep some
molecules sticking together. They are weak & also known
as van der waal’s forces, named after a chemist whose name
was not Arbuiso.
The first weak force holding
molecules together are called
dipole forces. They are due
to the dipole (positive and
negative) attractions between
different sides of molecules
to each other. The force is
ELECTROSTATIC, but much weaker
than the electrostatic forces
holding ionic bonds together.
This happens with polar
molecules that DO NOT CONTAIN
hydrogen (like water).
Dr. Van der Waal, the weak force chemist.
The other weak force is called dispersion
force, which is due to the movement of
molecules and to the number of electrons
around. They create temporary but real
attractions between molecules.
The more electrons, the more dispersion force. For example,
both F and Cl are gases at STP because there are not too
many electrons in these atoms. Br makes a liquid at STP and
there are lots more electrons in bromine compared to the first
2 atoms.
Iodine has the most electrons of all in group 17 and it’s a solid
at STP. More electrons make for more forces (all the while
temperature and pressure were constant).
When you have a lot of electrons and they are all
buzzing around quickly from time to time a temporary
condition can be created where there are more electrons
over there than here. This creates a temporary but real
electrostatic force of attraction between the (+) and the
(-) zones created.
The more electrons you have (Iodine has lots more than
fluorine for example) the more opportunity for this
temporary condition to exist.
It’s weak but real and in group 17 at STP the results
make for some gases, a liquid and a solid at constant
STP.
… is the other force keeping molecules attracted to each
other always includes hydrogen. (hence this name!)
When hydrogen bonds to certain highly electro-negative
atoms such as oxygen, nitrogen or fluorine, the bonds are
very polar.
This leaves the hydrogen rather positive, wishing for some
negativity in the form of electrons. Since it can’t pull its
electron back from these atoms, it actually is attracted to the
UNSHARED PAIRS of electrons from other nearby
molecules.
The + signs in
blue are the
hydrogen
atoms without
electrons. See
how they can
be attracted to
the blue
UNSHARED
PAIRS of
electrons of a
nearby water
molecule? That
is hydrogen
bonding.
the hydrogen bond is only about
5% the strength of a covalent
bond, but much stronger than a
dipole weak bond
Read your diary.
Promise yourself that you’ll do 20 minutes per
night, Sundays through Thursdays (at least).
20 minutes = 15 extra points per celebration.
This is not really even an experiment, it’s true!
Just do it.
Peace, love, and chemistry…