Polar and NonPolar Molecules: How To Tell If a Molecule is Polar or Nonpolar

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