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Author Topic: URGENT HOMEWORK HELP  (Read 7083 times)

Offline Carolyn

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URGENT HOMEWORK HELP
« on: 07/11/2006 00:04:33 »
Someone please help. My best friends daughter called me tonight and asked me to google this question: 

The molecules H2O & CCL4 are non polar as the central atoms O & C respectively are SP3 hybridized.  True or False.


I couldn't find an answer, of course I have no idea what I'm looking for.  This is a homework assignment and is due tomorrow.  If anyone could help with the answer and possibly an explanation we would be most grateful.

Carolyn


 

another_someone

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Re: URGENT HOMEWORK HELP
« Reply #1 on: 07/11/2006 00:59:27 »
Don't know what SP3 hybridized is meant to mean, but as I understand it, water is polarised (if by that you are referring to the water molecule being an electric dipole), and CCl4 is not.

http://en.wikipedia.org/wiki/Water_(molecule)
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An important feature of water is its polar nature. The water molecule forms an angle, with hydrogen atoms at the tips and oxygen at the vertex. Since oxygen has a higher electronegativity than hydrogen, the side of the molecule with the oxygen atom has a partial negative charge. A molecule with such a charge difference is called a dipole. The charge differences cause water molecules to be attracted to each other (the relatively positive areas being attracted to the relatively negative areas) and to other polar molecules. This attraction is known as hydrogen bonding, and explains many of the properties of water.
 

another_someone

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Re: URGENT HOMEWORK HELP
« Reply #2 on: 07/11/2006 01:03:05 »
OK, I have found reference to SP3 hybridisation:

http://bouman.chem.georgetown.edu/molecorbs/mosp3.htm
Quote
sp3 Hybridization

sp3 hybridization describes the bonding in tetrahedral or near-tetrahedral molecules such as methane.

Since CCl4 is an analogue of methane, it will this form a similar near-tetrahedral structure; but water is very different, and will not.
 

Offline Carolyn

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Re: URGENT HOMEWORK HELP
« Reply #3 on: 07/11/2006 01:15:47 »
Thanks George.  I appreciate your help.

Carolyn
 

Offline lightarrow

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Re: URGENT HOMEWORK HELP
« Reply #4 on: 07/11/2006 08:44:50 »
The SP3 hybridization it's not related with molecular polarity at all, unless the central atom is bond with 4 equal atoms (like CCl4 ecc.). Water is Very polar and CCl4 is Completely non polar. This is a classical question to show how hybridization and polarity are not related at all. The water polarity is due to the fact that:

1. There is a charge separation inside the molecule, because H and O have different electronegativities.
2. The molecule is asymmetric, so other molecular species can feel this charge separation. Example: NaCl dissolve in water because Na+ ions are attracted from oxygen and Cl- ions are attracted from hydrogen.

Since C and Cl have different electronegativities (there always is between two different atoms), there is a charge separation in CCl4, but the molecule is completely simmetric, so No dipole moment, so no charged or polarized species are influenced by this charge separation.

Result: polar species are Completely insoluble in CCl4, e.g. water itself!
 

Offline eric l

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Re: URGENT HOMEWORK HELP
« Reply #5 on: 07/11/2006 12:50:01 »
This SP3-hybridization is typical for the carbon atom (although it may occur with some silicon compounds).  It means that the electrons in the S- and P-orbitals are "redistributed" over 4 SP3 orbitals.  In carbon, you can also have SP-hybridisation, that is when you have so-called double bounds as in ethene (ethylene).
This means that in an SP3-hybridization, you have four equivalent bounds, stretching from the center of a tetrahedron (the carbon-atom) to the corners.  If we have the same atoms on the other ends of the bounds, we have no polarity, no matter if these atoms are hydrogen or chlorine (provided they are hydrogen all four of them, or chlorine all four of them).
With H2O, you have only two bonds stretching from the central oxygen-atom.  These two bonds will not lie diametrically opposed, but at an angle of about 105.  Because of this, there is an asymmetry in the molecule, and because of the difference in electronegativiy between oxygen and hydrogen, you have polarity.
Now some will explain this angle of about 105 by SP3-hybridization, but with oxygen you have only two bounds available, while you had four with carbon.
 

Offline Cut Chemist

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Re: URGENT HOMEWORK HELP
« Reply #6 on: 21/11/2006 23:50:21 »
The electron geometry of H2O is tetrahedral.
-because it has two lone pairs of electrons attached to the oxygen.  That makes it Sp3 hybridized also.

The molecular geometry is bent

Normal tetrahedral bond angles are 109.5 degrees, but the lone pairs of electrons push the hydrogens a little closer together, (to 105 degrees)

The answer to the question is false.

It's a trick question.
sp3 hybridization has nothing to do with polarity.

-but you are correct..  eric I, 

"Because of (the differing electronegativities and dipole interactions), there is an asymmetry in the molecule, and because of the difference in electronegativiy between oxygen and hydrogen, you have polarity."
 

The Naked Scientists Forum

Re: URGENT HOMEWORK HELP
« Reply #6 on: 21/11/2006 23:50:21 »

 

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