Which of these are polar molecules?

[Mr Rayon]

Methane (CH4), ammonia (NH3), water (H2O), hydrogen chloride (HCl), butane (C4H10), phosphine (PH3), oxygen (O2), carbon dioxide (CO2), ethene (C2H4), nitrogen (N2), ethyne (C2H2).

 

And how do you know?

 

 

Please someone respond in less than an hour!

[Cap'n Refsmmat]

Do you know how to draw Lewis structures? If so, you need to draw them. Then it's a matter of figuring out which atoms in the molecule are the most electronegative. (The electronegative ones will attract more electrons, making them negative. This makes the molecule polar.)

 

I've left out a good bit of detail there but hopefully that'll be enough to jog your memory.

[UC]

Do you know how to draw Lewis structures? If so, you need to draw them. Then it's a matter of figuring out which atoms in the molecule are the most electronegative. (The electronegative ones will attract more electrons, making them negative. This makes the molecule polar.)

 

I've left out a good bit of detail there but hopefully that'll be enough to jog your memory.

 

Not quite. It's more about molecular geometry than anything. For example, carbon tetrachloride has 4 very electronegative chlorines surrounding a less electronegative carbon atom, but due to the molecular geometry (tetrahedral), it has 0 net dipole moment.

[Cap'n Refsmmat]

Hence having to draw Lewis structures. We did those to figure out molecular geometry.

 

Perhaps I should have been clearer. You have to figure out which molecules are the most electronegative in terms of the Lewis structure/geometry to get an idea of whether one "end" is more electronegative than another.

[hermanntrude]

the Lewis structure provides no information on the molecular geometry, althought it is certain the first step.

 

-draw the Lewis diagram (look in your textbook and notes for the rules to complete this step)

-use VSEPR to determine the electron group geometry and then the molecular gemoetry (again, info on how to do this will be in your textbook and notes)

-the last step is often the hardest. If you've studied vectors it helps, because then you can simply treat the dipoles on each bond as vectors and combine them to see if there is a resultant vector (resultant dipole). Otherwise try to look for asymmetry. If a molecule has an asymmetric shape (T-shape, trigonal pyramidal, etc), and the bonds involved have dipoles on them, there will be a resultant dipole. If the shape is symmetrical but the outer atoms are different to each other (chloromethane is a good example), then there will also be a dipole.

[ShadowReeves]

well the answer is ammonia NH3, it is poler which allows it to become NH4

[John Cuthber]

well the answer is ammonia NH3, it is poler which allows it to become NH4

 

I guess you also didn't get the bit about responding in less than an hour.

 

H2O is polar and forms H3O+

A few of the others are too, but I don't want to spoil the fun.

[hermanntrude]

I guess you also didn't get the bit about responding in less than an hour.

 

H2O is polar and forms H3O+

A few of the others are too, but I don't want to spoil the fun.

 

haha i guess i didn't spot that bit, eh?

 

Oh well. if by some remote chance, a member uses the search function and finds this thread when looking for help determining polarities of molecules, now they'll have a full answer.

 

ShadowReeves, we don't give out the answers here we try to help people find it themselves. Plus your answer was only one of many. there's more than one.

[John Cuthber]

Never trust a man who spells "polar" wrongly in a thread where he only had to look at the title to find the corect spelling.