Which Bond is More Polar: Carbon Hydrogen or Phospohorous Hydrogen?

[dacruick]

I had a question in a lab about which elements are least likely to form polar covalent bonds with hydrogen. From what I understand, what governs how polar a bond is, is the electronegativity of the element. The answer said that Carbon was the one which was least likely to form the bond, but using my periodic table I see that phosphorous has the same electronegativity as hydrogen.

So shouldn't phosphorous share the bond most evenly? I've asked a couple other people and they say that phosphorous might be an exception because it can expand its octet...but that doesn't make sense to me.

Thank you,

dacruick

 

[jbsteele]

The answer you were given is correct. Carbon is the least likely element to form a polar covalent bond with hydrogen because it has the lowest electronegativity of the elements listed. Phosphorus does have a higher electronegativity than hydrogen, but it also has the ability to expand its octet. This means that it can form more than just a single covalent bond, which can lead to a more non-polar bond. Thus, even though phosphorus has a higher electronegativity, it is still less likely to form a polar covalent bond with hydrogen than carbon.