Chemistry Question: About polar and nonpolar bonds.

[Turkish]

I got a test tomorrow and one of the practice questions, it asks us to determine if the below are polar or nonpolar. I know HCN and NO2 are polar and CO2 is nonpolar, but I don't know why. Any chemists to help me out here? 🙂 Thanks.

 

[StevenYoo]

Originally posted by: Xiety
I got a test tomorrow and one of the practice questions, it asks us to determine if the below are polar or nonpolar. I know HCN and NO2 are polar and CO2 is nonpolar, but I don't know why. Any chemists to help me out here? 🙂 Thanks.

well, first there are electronegativities. if the difference between the EN's of the cation and anion are greater than 1.7, then u got an ionic bond. greater than 0, but less than 1.7, u got a polar covalent. and 0 is a non polar bond.

but there is also a matter of molecular structure. CO2 is a linear molecule, the polar covalent C-O bonds cancel each other kinda, so the molecule is nonpolar. same for CH4 and such.

HCN and NO2 are not symmetrically shaped molecules. add that with the electronegativity thing, and so they're polar.

QED?

 

[Turkish]

Originally posted by: GuybrushThreepwood

Originally posted by: Xiety
I got a test tomorrow and one of the practice questions, it asks us to determine if the below are polar or nonpolar. I know HCN and NO2 are polar and CO2 is nonpolar, but I don't know why. Any chemists to help me out here? 🙂 Thanks.

well, first there are electronegativities. if the difference between the EN's of the cation and anion are greater than 1.7, then u got an ionic bond. greater than 0, but less than 1.7, u got a polar covalent. and 0 is a non polar bond.

but there is also a matter of molecular structure. CO2 is a linear molecule, the polar covalent C-O bonds cancel each other kinda, so the molecule is nonpolar. same for CH4 and such.

HCN and NO2 are not symmetrically shaped molecules. add that with the electronegativity thing, and so they're polar.

QED?

Hmmm. Weird. are you sure about the numbers, because i thought in order to get a polar covalent bond, the difference between ENs of two atoms should be between 0.5 and 2.0? or am i wrong? If it is less than 0.5, it's non covalent, and if it's bigger than 2.0, ionics are formed? Am i wrong about this stuff?

 

[StevenYoo]

Originally posted by: Xiety

Originally posted by: GuybrushThreepwood

Originally posted by: Xiety
I got a test tomorrow and one of the practice questions, it asks us to determine if the below are polar or nonpolar. I know HCN and NO2 are polar and CO2 is nonpolar, but I don't know why. Any chemists to help me out here? 🙂 Thanks.

well, first there are electronegativities. if the difference between the EN's of the cation and anion are greater than 1.7, then u got an ionic bond. greater than 0, but less than 1.7, u got a polar covalent. and 0 is a non polar bond.

but there is also a matter of molecular structure. CO2 is a linear molecule, the polar covalent C-O bonds cancel each other kinda, so the molecule is nonpolar. same for CH4 and such.

HCN and NO2 are not symmetrically shaped molecules. add that with the electronegativity thing, and so they're polar.

QED?

Hmmm. Weird. are you sure about the numbers, because i thought in order to get a polar covalent bond, the difference between ENs of two atoms should be between 0.5 and 2.0? or am i wrong? If it is less than 0.5, it's non covalent, and if it's bigger than 2.0, ionics are formed? Am i wrong about this stuff?

could be a different scale than the one i'm used to? stick with whatever ur text/professor told u.

but just know that it's not only electronegativities that come into play here.

 

[minendo]

Originally posted by: Xiety
Hmmm. Weird. are you sure about the numbers, because i thought in order to get a polar covalent bond, the difference between ENs of two atoms should be between 0.5 and 2.0? or am i wrong? If it is less than 0.5, it's non covalent, and if it's bigger than 2.0, ionics are formed? Am i wrong about this stuff?

You are right.

 

[Turkish]

ok, so still, i dont understand why HCN is polar. Here are the EN values for them.
H: 2.1
C: 2.5
N: 3.0
Can you explain, looking through these numbers, how HCN is polar? 😱

 

[minendo]

Originally posted by: Xiety
ok, so still, i dont understand why HCN is polar. Here are the EN values for them.
H: 2.1
C: 2.5
N: 3.0
Can you explain, looking through these numbers, how HCN is polar? 😱

Nitrogen end holds a slightly negative charge while the hydrogen holds a slightly positive charge.

 

[StevenYoo]

Originally posted by: minendo

Originally posted by: Xiety
ok, so still, i dont understand why HCN is polar. Here are the EN values for them.
H: 2.1
C: 2.5
N: 3.0
Can you explain, looking through these numbers, how HCN is polar? 😱

Nitrogen end holds a slightly negative charge while the hydrogen holds a slightly positive charge.

i think i have to agree with this.

 

[Turkish]

Originally posted by: minendo

Originally posted by: Xiety
ok, so still, i dont understand why HCN is polar. Here are the EN values for them.
H: 2.1
C: 2.5
N: 3.0
Can you explain, looking through these numbers, how HCN is polar? 😱

Nitrogen end holds a slightly negative charge while the hydrogen holds a slightly positive charge.

so the C in the middle doesn't matter at all?

So i need to look at the EN difference between the outer elements and see what range they fall in?

 

[minendo]

Originally posted by: Xiety

Originally posted by: minendo

Originally posted by: Xiety
ok, so still, i dont understand why HCN is polar. Here are the EN values for them.
H: 2.1
C: 2.5
N: 3.0
Can you explain, looking through these numbers, how HCN is polar? 😱

Nitrogen end holds a slightly negative charge while the hydrogen holds a slightly positive charge.

so the C in the middle doesn't matter at all?

So i need to look at the EN difference between the outer elements and see what range they fall in?

Think dipole moments.

 

[Turkish]

Originally posted by: minendo

Originally posted by: Xiety

Originally posted by: minendo

Originally posted by: Xiety
ok, so still, i dont understand why HCN is polar. Here are the EN values for them.
H: 2.1
C: 2.5
N: 3.0
Can you explain, looking through these numbers, how HCN is polar? 😱

Nitrogen end holds a slightly negative charge while the hydrogen holds a slightly positive charge.

so the C in the middle doesn't matter at all?

So i need to look at the EN difference between the outer elements and see what range they fall in?

Think dipole moments.

Argh I am not very good with chemistry, but isnt a dipole when the charged ends do not cancel each other? how is it related? I am sorry for all these stupid questions. I am not good with chemistry, so thanks for explaining mimendo / guybrush.

 

[minendo]

Originally posted by: Xiety

Originally posted by: minendo

Originally posted by: Xiety

Originally posted by: minendo

Originally posted by: Xiety
ok, so still, i dont understand why HCN is polar. Here are the EN values for them.
H: 2.1
C: 2.5
N: 3.0
Can you explain, looking through these numbers, how HCN is polar? 😱

Nitrogen end holds a slightly negative charge while the hydrogen holds a slightly positive charge.

so the C in the middle doesn't matter at all?

So i need to look at the EN difference between the outer elements and see what range they fall in?

Think dipole moments.

Argh I am not very good with chemistry, but isnt a dipole when the charged ends do not cancel each other? how is it related? I am sorry for all these stupid questions. I am not good with chemistry, so thanks for explaining mimendo / guybrush.

Dipoles occur when one molecule pulls the electrons harder than another. This means the electrons spend more time at that area creating a partial negative charge while a partial positive charge is found at the other end.

 

[Turkish]

darn i still dont get it but i m not gonna bother you anymore :-\ thanks for the help again....

 

[SportSC4]

look at its configuration. it's linear, H-C-N or 2.1-2.5-3.0. Carbon pulls on Hydrogen and Nitrogen pulls on Carbon. the entire equation pulls to the right. a non-polar molecule would cancel itself. Using CO2 as an example, it lines up as O=C=O (3.5-2.5-3.5). Oxygen pulls on Carbon and both ends and no net movement occurrs.

 

[Turkish]

Originally posted by: SportSC4
look at its configuration. it's linear, H-C-N or 2.1-2.5-3.0. Carbon pulls on Hydrogen and Nitrogen pulls on Carbon. the entire equation pulls to the right. a non-polar molecule would cancel itself. Using CO2 as an example, it lines up as O=C=O (3.5-2.5-3.5). Oxygen pulls on Carbon and both ends and no net movement occurrs.

oh sweet, i got it! great! thanks a lot man 🙂 appreciated!