Unhybridized orbitals


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Christine Inyoung Chung 1F
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Joined: Fri Sep 25, 2015 3:00 am

Unhybridized orbitals

Postby Christine Inyoung Chung 1F » Sat Oct 31, 2015 3:52 pm

I am still a little bit confused about the purpose of unhybridized orbitals when determining an atom's hybridization. Is it mainly to fill up all the number of electrons (because the number of orbitals is conserved) or is there another significance to it? Also if the hybridized orbitals fill up all the number of electrons will there be no unhybridized orbitals?

Divya Prajapati 1E
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Joined: Fri Sep 25, 2015 3:00 am

Re: Unhybridized orbitals

Postby Divya Prajapati 1E » Sun Nov 01, 2015 3:22 pm

The main function of unhybridized orbitals is usually to form double bonds. Consider each of the following cases:

- sp3 hybridization has 4 sp3 hybridized orbitals and 0 unhybridized orbitals. These allow molecules to form 4 sigma bonds.
- sp2 hybridization has 3 sp2 hybridized orbitals and 1 unhybridized p orbital. This allows molecules to form 3 sigma and 1 pi bond (remember that a double bond has a 1 sigma AND 1 pi bond)
- sp hybridization has 2 sp hybridized orbitals and 2 unhybridized p porbitals. This allows molecules to from 2 sigma and 2 pi bonds (allowing 2 double bonds).

Based on this information, you can see that the total number of orbitals is conserved, with 4 total. This matches the fact that we begin with 1 s and 3 p orbitals, thus ensuring that the number of electrons remains the same as well.

To answer your final question, if hybridized orbitals "use up" all the electrons (as is the case with sp3 hybridization), there will indeed be no unhybridized orbitals. This is the same as saying there are 8 electrons available and no need to form double bonds (which require unhybridized p orbitals).

Katherine Fitzgerald 1A
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Joined: Fri Sep 29, 2017 7:05 am

Re: Unhybridized orbitals

Postby Katherine Fitzgerald 1A » Tue Jul 30, 2019 11:28 am

Thanks, Divya! Your explanation was very thorough and helpful.

Can anyone walk through the same process / logic here for unhybridized/unhybridized orbitals when there are d orbitals involved (how many hybrid orbitals, how any unhybridized, number of sigma and number of pi bonds)?

Katherine Fitzgerald 1A
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Joined: Fri Sep 29, 2017 7:05 am

Re: Unhybridized orbitals

Postby Katherine Fitzgerald 1A » Tue Jul 30, 2019 11:42 am

For instance, would we say that for dsp3, one of the 2s electrons is promoted to a 3d orbital, leading to 5 hybridized dsp3 orbitals? Does that mean that there are then 4 unhybridized d orbitals left over? what types of bonds do those empty 3 orbitals form?

Chem_Mod
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Re: Unhybridized orbitals

Postby Chem_Mod » Tue Jul 30, 2019 1:12 pm

Some elements in period 3 and later periods can accomodate five or more electron pairs, as in PCl5. To account for the trigonal bipyramidal arrangement of five electron pairs, we use one d-orbital as well as all the valence s- and p- orbitals of the atom. The resulting five orbitals are called sp3d hybrid orbitals. For example, in PF5, a d-orbital is required to accomodate all the valence electrons. If we need six orbitals to accomodate six electron pairs around an atom in an octahedral arrangement (ex. SF6), we need to use two d-orbitals in addition to the valence s and p orbitals to form six sp3d2 hybrid orbitals.

Bella Martin
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Re: Unhybridized orbitals

Postby Bella Martin » Tue Jul 30, 2019 10:56 pm

and empty hybridization orbitals allow for pi bonding, right?

Chem_Mod
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Re: Unhybridized orbitals

Postby Chem_Mod » Tue Jul 30, 2019 11:13 pm

Unhybridized p orbitals allow for pi bonding, not empty hybridized orbitals. Take for example an sp2, you would have the 3 hybridized sp2 orbitals, and then remember you would still have a leftover p orbital (you had 4 total- 1 s and 3 p's), so that leftover p orbital can make the pi bond, resulting in a double bond.


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