polarity

hi there , got a question for u how can u tell wheter the polarity of the following sets are of a higer polarity . is there a formula ? sorry jus a guy new to the chem world.
eg C-F , O-F , Be-F Thanks.

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Fairly new to the English language too, by the looks of it ;-)

Anyways - yes - there is a way to tell how polar a bond will be.
Some elements like to grab electrons in a bond more than others.
We call this property "electronegativity".
You can look up an element's electronegativity in data tables (for instance, on this site)
The greater the difference between the two element's electronegativity, the more polar a bond between them will be.

The most electronegative element is fluorine, with a value of "4" units.
The least electronegative ( or "most electropositive" element is probably Francium, with a value nearer 1.
(As you can see, the values only go up to 4!)

Shape of the molecule is also very important. For example, in CCl[size=9]4[/size] difference between electronegativities of C and Cl is 0.7, but the molecule is not polar (because of its shape).

http://home.kooee.com.au/matthew/uni/right.htm
http://fy.chalmers.se/~brodin/MolecularMotions/nu1anim(crop).gif

[quote="<chem>"]Shape of the molecule is also very important. For example, in CCl[size=9]4[/size] difference between electronegativities of C and Cl is 0.7, but the molecule is not polar (because of its shape).

http://home.kooee.com.au/matthew/uni/right.htm
http://fy.chalmers.se/~brodin/MolecularMotions/nu1anim(crop).gif[/quote]

True, but each [i]individual[/i] bond is polar. The molecule on the whole is not, but on a C-Cl scale, there is polarity. This is where semantics really makes you want to rip your eyes out. lol. :D

Feline: Flourine isn't the most electronegative element. It's a common mistake. If electronegativity is the tendecy for an atom to keep electrons around it. Can you think of any other atoms that want to keep it's electrons around it so much that they don't even want to bond to anything else?

[quote="UCB Mitch"]Feline: Flourine isn't the most electronegative element. It's a common mistake. If electronegativity is the tendecy for an atom to keep electrons around it. Can you think of any other atoms that want to keep it's electrons around it so much that they don't even want to bond to anything else?[/quote]

According to every source I've ever seen, Fluorine has the highest electronegativity at approximately 4.

It would be Helium. Electronegativity is the (ionization energy + electron affinity)/2 . The amount of energy to ionize helium is considerably high.

[quote="UCB Mitch"]It would be Helium. Electronegativity is the (ionization energy + electron affinity)/2 . The amount of energy to ionize helium is considerably high.[/quote]

That's where differing definitions of electronegativity cause problems. The usual definition is the "measure of the tendency of an atom to attract electrons in a chemical bond." Since Helium doesn't form any chemical bonds, it can't have an electronegativity. This is why it would be really great if teachers/professor would stick to using one definition and have that be uniform across the world.

The electronegativity definition you're using is Paulings. He used bond lengths as the measure of electronegativity. So on his system Helium would be undefined.

Then how about cations?

you can still ionize a cation, and cation's definately still have an electron affinity, so a electronegativity can be assigned to them.

WebElements: the periodic table on the WWW [http://www.webelements.com/]

Copyright 1993-20010 Mark Winter [The University of Sheffield and WebElements Ltd, UK]. All rights reserved.