Question

How to distinguish between polar and non-polar molecules/compound? For instance, one that you have not studied before but have to know if its polar or non-polar. Can you distinguish it from the basic structure of the molecule?

For instance, Bromine Br_2; at first I thought it was polar but then its not non-polar..so how can you tell?

Answer 1

You can instantly tell if a molecule is polar if you look at the electronegativity differences between two differing atoms. The larger the difference between electronegativity values, the more polar the molecule is.

Answer 2

halcyon is right. Do you have an electronegativity chart? Some are different from others. IS there one in your text book? If not I can find you one, but its better to use what your teacher supplies you with.

Answer 3

But a non-polar molecule would have an electrongativity differences as well; i think.

and electronegativity charts are not provided in exams here

is it possible to distinguish it from the structure of the molecule?

Answer 4

Not sure about how to find the answer from structure.

"But a non-polar molecule would have an electrongativity differences as well; i think." You are right. The way you determine the status is to see to which degree of difference is apparent.

Answer 5

http://4.bp.blogspot.com/__E1v9cAjiVs/TMjVxHpJbWI/AAAAAAAAABU/JW1YuKX9-s4/s1600/electronegativity+table.jpg

Answer 6

What if I dont know anything about the molecule; like if its polar or non-polar how am i able to distinguish?

If i remember correctly, you can determine it by the structure..but i cant remember how

Answer 7

http://www.green-planet-solar-energy.com/images/PT-small-electroneg.gif

Answer 8

What about this link: http://www.tutor-homework.com/Chemistry_Help/Molecular_Geometry/Polar_Or_Nonpolar.html

Answer 9

that will be hard tho; to remember the electronegativity of all elements..

Answer 10

this is true....i dont think any teacher would expect that. With out the chart, that method is dead

Answer 11

but it is easy

Answer 12

with the chart

Answer 13

all ionic bonds are polar right?

Answer 14

what about this: http://preparatorychemistry.com/bishop_molecular_polarity.htm

Answer 15

well i would like a method without the electronegativity chart

Answer 16

(if possible)

Answer 17

that last link i believe is that kind of method...without the chart

Answer 18

i read it..stil needs the chart

Answer 19

lame...ok one sec

Answer 20

All ionic bonds are polar. Electronegativity differences are taken into account with covalent bonds. If it's a compound such as F2 then no, it's not polar cause of the same electronegativity

Answer 21

I think I asked my teacher if there was a way and he said no...

Answer 22

well what if you dont know if its an ionic bond or not..how would you know if its polar or non-polar?

Answer 23

well metals and non metals make inonic bonds

Answer 24

You can always make an educated guess if you know if an element is metal or non metal or if you know if an element is on the left or right or top or bottom of the per table

Answer 25

bottom left is real small.....top right of table is real big

Answer 26

Fr = 0.7 F = 4.0

Answer 27

It's entirely about the structure, like you were thinking! Basically symmetry means non-polar and asymmetry means polar. So Br2 has two atoms with the same EN; you can imagine their electron withdrawing strength canceling out one another's pull so that there's no net pull in the structure and the whole thing is non-polar.

In contrast, something like CO would have a net polarity because even if you can't remember what the EN of C of O is, you still know that one half of that molecule is going to pull the electrons a little more than the other. That gives the molecule a net polarity.

It helps if you just draw a little arrow pointing in the direction of the Electron withdrawing activity. Then you can see if there's a net pull or if there are arrows that cancel one another out.

Answer 28

u cn find d difrnc simply by evaluatng d electronegativity o strucure. evn the aarangemnt in d periodic table l gv u an idea of the polarity b/w molecules,atoms,elemnts

Answer 29

okay, thanks benjaminf

but for the structure; is it the molecular structure? the chemical formula structure or what? They just look symmetrical to me.

Answer 30

it's based on what elements comprise the structure and also on the molecular structure.

Answer 31

well how can you see it from the molecular stucture?

Answer 32

a simple way to see if you can make the 2 sides balance

Answer 33

For example, Bromine Br_2' how are able to balance/ see it?

Answer 34

if you cut the molecule in 1/2, one side will have 1 Br and the other another Br, so it's balanced thus non-polar

Answer 35

so another example, NaCl, one side has Na other side Cl, 2 different elements, thus polar

Answer 36

this applies only to certain molecules though, it's just a simple way of looking at things

Answer 37

okay i got it. what about molecules is there a legit way?

Answer 38

about other molecules*

Answer 39

yes, you have to look at their electronegativity (how much they attract electrons). If there is high electronegativity differences it's most likely a polar bond (e.g. NaCl). But if they got close to no difference (e.g. C-H), then it's a non-polar bond.

Answer 40

on top of that, you have to use the 1st rule i mentioned above, a polar bond may be cancelled out by another polar bond on the exact opposite side...e.g. CCl4, even tho the C-Cl bonds are polar, the exact conformation of the molecule allows all the polarity to cancel out to 0

Answer 41

i got it thanks.