[Frater EIE]

Hello
I am new to chemistry and am studying it on my own. So I'm sure I will have a lot of questions in the next little while... Which is why I really appreciate an online forum like this one.

I've just learned about electronegativity difference  (^en) in chemical bonding. But I am confused about it. In my book, it says that if ^en is less than .5 units then the bond is covalent, if it is between .5 and 1.5 ^en then it is polar covalent, and if it is greater than 1.5 it is ionic. But then a few sentences later, it says "To be sure, any difference in electronegativities will result in a polar bond."

This seems to be a blatant contradiction. Can someone please clear this up for me?

Thank you
Mica

[Arkcon]

Yeah, the second statement seems to match what they have in Wikipedia (a pretty good source for common factual info such as this) -- even a slight electronegativity difference will result in some small polarity to the covalent bond.

http://en.wikipedia.org/wiki/Chemical_bond#Ionic_bond

We see this sometimes in organic chemistry.  Carbon - carbon bonds are as covalent as can be, because they're the same thing.  Even though the presence of oxygen or nitrogen in  an orgainic molecule is still covalent, they become the site for chemical attack.

[fledarmus]

It is just a question of degree. Like saying people below five feet tall are short, people from five feet to six feet are pretty average, and people above six feet are tall. Any two people will have some difference in height, but even though one short person might be taller than another short person, that wouldn't make him or her a tall person. Any bond between atoms of different electronegativies will have some polarity, but if the electronegativies are close enough, you wouldn't exactly describe it is a polar bond.