in this video we are going to go over a
way that we can quickly distinguish a
polar molecule from a non-polar molecule
now it's easier if you know what to look
for when a molecule is nonpolar and
before you find out what to look for
when it's polar the first category of
nonpolar molecules are those that are
made up of one element for example if
you have a mono atomic atom or a
diatomic atom that's completely positive
one element it's nonpolar
examples include for example and -
that's the diatomic molecule o2 CL 2 F 2
h2 these are all nonpolar and some of
the mono atomic gases like helium neon
argon xenon under normal gases those are
also nonpolar the next category you look
for is a molecule that contains only
carbon and hydrogen those molecules are
nonpolar so for example in methane your
alkanes ethane c2h6 I think ch2 double
bond CH 2 these are composed only of
carbon and hydrogen and therefore they
are nonpolar the carbon hydrogen bond is
nonpolar the third area to look for is
if the molecule has symmetry so for
example carbon tetrafluoride notice that
all of the outer elements are the same
this molecule has symmetry this is
nonpolar sulfur hexagons
all four hexa bromide all of the outer
elements are identical this molecule is
also nonpolar carbon dioxide another
nonpolar molecule
the two outer elements the oxygens are
the same phosphorus trichloride
that's another nonpolar molecule each of
these molecules they have symmetry as
you can see BH dream boron try hydride
also nonpolar now let's let's see if the
molecule acts symmetry is it always
gonna be polar well it all depends on
the en difference if the
electronegativity difference if it's a
less than 25 then it's gonna be nonpolar
if it's more polar let me give you an
example of that
so iodine mono bromide iodine has an
electronegativity value of 2.5 and for
bromine it's about 2.8 because the en
difference is like 23 this bond is
relatively nonpolar another example if
there's no symmetry is bromine mono
chloride chlorine has an
electronegativity value of 3.0 and here
once again the en difference is less
than 0.5 so that molecule is nonpolar so
those are some quick ways that you can
use to identify if molecule is nonpolar
if it doesn't meet those characteristics
generally it's gonna be polar so what
are some quick ways to identify polar
molecules the first thing is if you see
if a molecule has hydrogen bonding it's
gonna be polar
so if hydrogen is directly attached to
nitrogen oxygen or fluorine it's polar
examples include water nh3 hf ch3oh even
though the carbon hydrogen bond is
non-polar the presence of the alcohol
means that you have hydrogen bonding and
therefore it's gonna be polar
ch3 and h2 because of the NH 2 it's
polar ch3cooh once again because of the
OHS folding now also if the molecule
acts symmetry and if the bond is polar
then it's gonna be a polar molecule
here's another example here the oxygens
here these oxygens are identical and it
has symmetry which makes it nonpolar
here this molecule it does not have
symmetry like this one did carbon has an
electronegativity value of 2.5 the
oxygen is 3.5 so this bond is polar here
for sulfur is also 2.5 so that carbon
sulfur bond is the nonpolar but because
of the carbon oxygen bond it's polar in
the case on the right when we have
carbon dioxide even though the carbon
oxygen bond is polar because there's two
of them because of the symmetry those
two - limits cancel out and therefore
co2 is nonpolar but if you replace one
of the oxygens with a sulfur molecule
then it becomes polar let's look at
another example
ch3 F
notice that it's similar to to this
molecule right here the carbon fluorine
bond is very polar carbon has an
electronegativity value of 2.5 and
fluorine it's 4.0 it's well above that
point five difference and so because of
the carbon fluorine bond its fuller the
carbon hydrogen bond is relatively
nonpolar so the dipole moments are very
small for that but in this case over
here these dipole moments they cancel
and that's why because if you have
symmetry it makes it nonpolar but
because this molecule lack symmetry it's
gotta be polar
another example is sulphur dioxide
because sometimes the shape of the
molecule can affect the polarity see
carbon dioxide which looks very similar
to sulphur dioxide and the fact that
there's two oxygens and one atom in the
middle because carbon dioxide has Alenia
shape to dive moments they cancel but
because sulphur dioxide has a bent shape
the arrows the dipole moment they don't
cancel and you can see because of the
lone pair this molecule acts symmetry so
that also makes it polar the last
example if you look at nh3 even though
it has has hydrogen bonded which makes
it polar the geometry also makes the
polar as well if you draw the arrows
they all point towards the partially
negative fluorine atom and they point in
one direction they don't cancel and
that's another reason why this molecules
polar so just to review molecules that
are nonpolar tend to be diatomic
molecules that are composed of one
element or mono atomic atoms like noble
gases they can be pure hydrocarbons or
they could be molecules that have
symmetry where all of the outer elements
are the same if you see that 99% of time
it's going to be nonpolar if you don't
see it for the most part is part
we gonna be polar but just to be on the
safe side looked at the
electronegativity values if it's greater
than 25 draw the arrow from the
partially positive atom to the partially
negative atom and if the arrows don't
cancel then your molecule is going to be
in polar so hopefully this video will
help you to quickly distinguish polar
nonpolar molecules and I wish you well
in your general chemistry course