May 31, 2020, 07:52:14 PM
Forum Rules: Read This Before Posting


Topic: Potential Energy and Angle Strain  (Read 4758 times)

0 Members and 1 Guest are viewing this topic.

Offline AdiDex

  • Full Member
  • ****
  • Posts: 305
  • Mole Snacks: +16/-12
  • Gender: Male
Potential Energy and Angle Strain
« on: November 03, 2015, 04:47:56 PM »
Let us consider a scenario , Two imaginary same atoms (A1  and A2 )with different hybridization (both are isolated and far apart from each other )  say one has sp3 another has sp2 .

Sp3 atom will be stable when it's bond angle between all 3 atoms is 180 and sp2  will be stable when it has 120° . (Here we were considering whole system , in case of calculating potential energy we have to sum the potential energy due to all possible repulsion
)

What if one of the bond angle between SP2 hybridized atom has 180° (Just reshape it and forget about  other 3 bonds ) , It will make the whole system unstable but i am not worried about it .

What if we only consider the potential energy due to repulsion between angle b1A2b2 and a1A1a2 . Which one will have higher potential energy ??

I got my answer from my primary knowledge of bonds (which i have done in my high school ) , we used to take help of a term known as ANGLE STRAIN .
So I thought to apply , and I applied. It's quite simple there is a angle strain in Sp2 hybridized  atom so it should have higher potential energy.

But I felt into more deeper and basic questions , They challenged my previous understandings . SO here we go ,
This term known as Angle strain , where did it come from ?? i reached on conclusion that it arouse from the summation of the potential energy of all possible interaction . Am i right ??
do we really consider angle Strain due to Increase in repulsion ??
or Bonds really act as a hard sticks , on bending them there is a increase in potential energy.
what's the matter ??

Simply answer me Why we consider angle strain ??

Offline AdiDex

  • Full Member
  • ****
  • Posts: 305
  • Mole Snacks: +16/-12
  • Gender: Male
Re: Potential Energy and Angle Strain
« Reply #1 on: November 03, 2015, 11:55:57 PM »
here is the picture of the molecule

Offline AdiDex

  • Full Member
  • ****
  • Posts: 305
  • Mole Snacks: +16/-12
  • Gender: Male
Re: Potential Energy and Angle Strain
« Reply #2 on: November 03, 2015, 11:58:17 PM »
Sorry i have written my question wrong , here is the corrected version

Let us consider a scenario , Two imaginary same atoms (A1  and A2 )with different hybridization (both are isolated and far apart from each other )  say one has sp another has sp2 .

Sp2 atom will be stable when it's bond angle between all 3 atoms is 120° and sp  will be stable when it has 180° . (Here we were considering whole system , in case of calculating potential energy we have to sum the potential energy due to all possible repulsion
)

What if one of the bond angle between SP2 hybridized atom has 180° (Just reshape it and forget about  other 2 bonds ) , It will make the whole system unstable but i am not worried about it .

What if we only consider the potential energy due to repulsion between angle b1A2b2 and a1A1a2 . Which one will have higher potential energy ??

I got my answer from my primary knowledge of bonds (which i have done in my high school ) , we used to take help of a term known as ANGLE STRAIN .
So I thought to apply , and I applied. It's quite simple there is a angle strain in Sp2 hybridized  atom so it should have higher potential energy.

But I felt into more deeper and basic questions , They challenged my previous understandings . SO here we go ,
This term known as Angle strain , where did it come from ?? i reached on conclusion that it arouse from the summation of the potential energy of all possible interaction . Am i right ??
do we really consider angle Strain due to Increase in repulsion ??
or Bonds really act as a hard sticks , on bending them there is a increase in potential energy.
what's the matter ??

Simply answer me Why we consider angle strain ??

Offline mjc123

  • Chemist
  • Sr. Member
  • *
  • Posts: 1751
  • Mole Snacks: +245/-11
Re: Potential Energy and Angle Strain
« Reply #3 on: November 04, 2015, 11:01:12 AM »
In an sp2 hybridised C atom, the sp2 orbitals are disposed at 120° from each other. To get maximum overlap with σ orbitals from bonded atoms, these atoms should also be at angles of 120° (as well as to reduce the repulsion between the bonded groups). If they are geometrically constrained to be at significantly different angles, the orbital overlap is reduced, the bonding molecular orbitals have higher energy and the antibonding ones lower, so the electronic energy (with electrons in the bonding orbitals) is higher.

Offline AdiDex

  • Full Member
  • ****
  • Posts: 305
  • Mole Snacks: +16/-12
  • Gender: Male
Re: Potential Energy and Angle Strain
« Reply #4 on: November 04, 2015, 10:28:11 PM »
In an sp2 To get maximum overlap with σ orbitals from bonded atoms, these atoms should also be at angles of 120°. If they are geometrically constrained to be at significantly different angles, the orbital overlap is reduced, the bonding molecular orbitals have higher energy and the antibonding ones lower, so the electronic energy (with electrons in the bonding orbitals) is high.
I am wondering how bond angle can affects the overlapping . Can you please elaborate it ??

Offline Irlanur

  • Chemist
  • Full Member
  • *
  • Posts: 422
  • Mole Snacks: +32/-4
Re: Potential Energy and Angle Strain
« Reply #5 on: November 05, 2015, 10:16:50 AM »
An isolated atom will always have the same "hybridisation".  In fact, the term doesn't really make much sense in this case.

Offline AdiDex

  • Full Member
  • ****
  • Posts: 305
  • Mole Snacks: +16/-12
  • Gender: Male
Re: Potential Energy and Angle Strain
« Reply #6 on: November 06, 2015, 01:33:07 AM »
Sorry i meant Isolated "Molecule" , specifically AB3 and AB2 molecules .

Offline Irlanur

  • Chemist
  • Full Member
  • *
  • Posts: 422
  • Mole Snacks: +32/-4
Re: Potential Energy and Angle Strain
« Reply #7 on: November 07, 2015, 10:28:55 AM »
First of all you will quickly run into problems because you don't have any meaningful reference states. how can you compare AB2 with AB3 ? they don't even have the same number of atoms.

Secondly: Angle strain is not "really a thing". it's sometimes helpful to remember or even predict some things, but it's definitely not a "hard" concept with consistent definitions. (as nearly everything in Organic Chemistry. Some say that's a weakness, some say this is THE advantage...).

Third: The geometry determines the Hybridisation, not the other way around.


Quote
I am wondering how bond angle can affects the overlapping . Can you please elaborate it ??
This is quite a general concept. It's also pretty obvious I think. If the orbital lobes do not directly point to the bonding partner, the overlap will be bad (at least in case of sigma bonds).

Offline AdiDex

  • Full Member
  • ****
  • Posts: 305
  • Mole Snacks: +16/-12
  • Gender: Male
Re: Potential Energy and Angle Strain
« Reply #8 on: November 08, 2015, 12:00:58 AM »
I have one more question .

SP2 hybrid has trigonal planar geometry to minimize the repulsion or it came from solving some equations ??

And thank you very much for clearing that Angle Strain is not a hard concept .
Now I know that there is nothing like angle strain , It's just a matter of extent of overlapping  ;D

Offline mjc123

  • Chemist
  • Sr. Member
  • *
  • Posts: 1751
  • Mole Snacks: +245/-11
Re: Potential Energy and Angle Strain
« Reply #9 on: November 12, 2015, 08:39:40 AM »
Quote
SP2 hybrid has trigonal planar geometry to minimize the repulsion or it came from solving some equations ??
Why shouldn't solving the Schrodinger equation give the geometry that minimises repulsion? It doesn't have to be either/or.

Offline Irlanur

  • Chemist
  • Full Member
  • *
  • Posts: 422
  • Mole Snacks: +32/-4
Re: Potential Energy and Angle Strain
« Reply #10 on: November 13, 2015, 12:36:56 PM »
Quote
Why shouldn't solving the Schrodinger equation give the geometry that minimises repulsion?

it doesn't. And usually we don't solve it exactly.

Offline AdiDex

  • Full Member
  • ****
  • Posts: 305
  • Mole Snacks: +16/-12
  • Gender: Male
Re: Potential Energy and Angle Strain
« Reply #11 on: November 17, 2015, 01:42:40 AM »
Quote
SP2 hybrid has trigonal planar geometry to minimize the repulsion or it came from solving some equations ??
Why shouldn't solving the Schrodinger equation give the geometry that minimises repulsion? It doesn't have to be either/or.

Got your point. My reply was totally silly .

Sponsored Links