The Student Room Group

Polarity

is there a way to see if a molecule is polar or non-polar? or do you just memorise the types of molecules that are polar/non-polar?
I heard you can use elctronegativities of elements to see if they're polar or not, would I have to memorise these values if I want to use this method?

all help is appreciated
thanks!
Original post by fzmannan
is there a way to see if a molecule is polar or non-polar? or do you just memorise the types of molecules that are polar/non-polar?
I heard you can use elctronegativities of elements to see if they're polar or not, would I have to memorise these values if I want to use this method?

all help is appreciated
thanks!


When two atoms have different electronegativity they produce a dipole.
Dipoles are vector quantities with both magnitude and direction.
Consequently, the dipoles in a molecule can be resolved into horizontal and vertical (and depth) components.
If there is an overall dipole after this resolution then the molecule is polar.

Although the above is a rigorous way to find out, it is often easier just to consider the symmetry of a molecule to decide whether or not the individual dipoles cancel out.

Check out: https://www.ibchem.com/IB16/02.32.htm
Original post by fzmannan
is there a way to see if a molecule is polar or non-polar? or do you just memorise the types of molecules that are polar/non-polar?
I heard you can use elctronegativities of elements to see if they're polar or not, would I have to memorise these values if I want to use this method?

all help is appreciated
thanks!


Hi there.

In general a large electronegativity difference between atoms = polar molecule and a small electronegativity difference between atoms = non-polar.

Fluorine is the most electronegative element on the periodic table and the elements the closer the element is to F, on the periodic table, the more electronegative it is e.g. N and O are the next more electronegative.

Hope this helps. :smile:

Thanks @charco for the edit :biggrin:
(edited 1 year ago)
Original post by triplexa
hi there.

In general a large electronegativity difference between atoms = polar molecule and a small electronegativity difference between atoms = non-polar.

Flourine is the most electronegative element on the periodic table and the elements the closer the element is to f, on the periodic table, the more electronegative it is e.g. N and o are the next more electronegative.


f l u o r i n e
Original post by TriplexA
Hi there.

In general a large electronegativity difference between atoms = polar molecule and a small electronegativity difference between atoms = non-polar.

Fluorine is the most electronegative element on the periodic table and the elements the closer the element is to F, on the periodic table, the more electronegative it is e.g. N and O are the next more electronegative.

Hope this helps. :smile:

Thanks @charco for the edit :biggrin:


Sorry, but it's one of my phobias.

My MSc dissertation was about hexafluorotitanium(IV) compounds. While driving a bunch of copies to the University on deadline day I noticed glancing at the pile that the bookbinder has spelled the title FLOURO, and I nearly had a heart attack.
I had to drive back to the bookbinder and get him to lift the gold-leaf letters and correct all the books. I made the deadline, but one by the skin of my teeth...
Original post by fzmannan
is there a way to see if a molecule is polar or non-polar? or do you just memorise the types of molecules that are polar/non-polar?
I heard you can use elctronegativities of elements to see if they're polar or not, would I have to memorise these values if I want to use this method?

all help is appreciated
thanks!

You can use electronegativities to predict polarity. The more electronegative element will be the δ- part of the dipole and the less electronegative element will be the δ+ part.

You can make a reasonable guess as to which elements are more electronegative. Typically, electronegativity increases along a period and decreases down a group. You can then use the positions of the elements on the periodic table to make your guesses. Note that fluorine is the most electronegative element, thus it is always δ- in a polar covalent bond.

As for the shapes of molecules, these can affect the overall polarity of the molecule. If the dipoles all face opposite directions, then the polarity cancels. A good example of this is carbon dioxide, which is linear. You can try drawing a 3D diagram of the molecule to make your prediction.
Original post by charco
Sorry, but it's one of my phobias.

My MSc dissertation was about hexafluorotitanium(IV) compounds. While driving a bunch of copies to the University on deadline day I noticed glancing at the pile that the bookbinder has spelled the title FLOURO, and I nearly had a heart attack.
I had to drive back to the bookbinder and get him to lift the gold-leaf letters and correct all the books. I made the deadline, but one by the skin of my teeth...

Don't apologise - I will double check my element spellings before posting. On this occasion I was rushing typing so made the fatal error. :biggrin:

That sounds painful but I'm glad you made the deadline! :smile:

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