Force between bonded atoms

  • #1
In a covalent bonded molecule, what is the force responsible for the molecule staying together. To my knowledge it's to do with electrons of opposite spins and being at a lower energy with valence shells filled but what is the force itself that pulls a second atom along if the atom it's bonded to is pulled?
 

Answers and Replies

  • #2
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The electromagnetic interaction. Pull one nucleus, and you stretch the electron orbital a bit, the electron gets a slightly higher wavefunction amplitude between the two atoms and follows the pulled nucleus partially, that also lets the second nucleus follow.
That is a very classical description, but it works surprisingly well.
 
  • #3
DrClaude
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To my knowledge it's to do with electrons of opposite spins and being at a lower energy with valence shells filled
H2+ is a counterexample to that. The bond comes in the first place because the electron(s) forming the bond get to interact with the other nucleus, and the orbital spreads over both nuclei, lower the electron's energy. The presence of electron density in between the nuclei also helps reduce their Coulomb repulsion.
 
  • #4
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The presence of electron density in between the nuclei also helps reduce their Coulomb repulsion.
I know that this is a common description, but I really don't like it. The force between the protons is not altered at all. You just get an attractive force between protons and electron(s) in addition.
 
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  • #5
The electromagnetic interaction. Pull one nucleus, and you stretch the electron orbital a bit, the electron gets a slightly higher wavefunction amplitude between the two atoms and follows the pulled nucleus partially, that also lets the second nucleus follow.
That is a very classical description, but it works surprisingly well.
So now I think about it, and please correct me or point out if it's a silly comment but would this be a result of the magnetic part of the electromagnetic force?
 
  • #6
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I don't think it is useful to split it into components here, but it is mainly the electric part. Nothing moves very fast here.
 
  • #7
I don't think it is useful to split it into components here, but it is mainly the electric part. Nothing moves very fast here.
In that case, I'm still not quite understanding how the bonded electrons enable each other to follow one another due to the electromagnetic force.
 
  • #9
Which part of post 2 is unclear?
The idea that a bond between two negative charges consists of electromagnetic interaction.
 
  • #10
DrClaude
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The bond is not between two electrons. The bond is between the atoms, due to the attraction of electrons and nuclei.
 
  • #11
DrDu
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Covalent bonding is a quantum mechanical effect. In a bond, the electrons have more space to move than in the field of a single atom. By the uncertainty principle, this reduces their momentum and thence also their kinetic energy.
 
  • #12
Covalent bonding is a quantum mechanical effect. In a bond, the electrons have more space to move than in the field of a single atom. By the uncertainty principle, this reduces their momentum and thence also their kinetic energy.
So how does the electromagnetic force come into this explanation sorry, if that's the force responsible?
 
  • #13
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The electromagnetic force is the interaction that holds everything together. It lets a nucleus attract electrons (and electrons attract nuclei).
 
  • #14
The electromagnetic force is the interaction that holds everything together. It lets a nucleus attract electrons (and electrons attract nuclei).
So would it be valid, to an extent to think of it in this sequence? Electron orbitals overlap forming larger area of electron density. Both nuclei are simultaneously attracted to this area holding the molecule together.
 
  • #15
Borek
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So would it be valid, to an extent to think of it in this sequence? Electron orbitals overlap forming larger area of electron density. Both nuclei are simultaneously attracted to this area holding the molecule together.
As a first approximation it sounds OK to me. Note, that it doesn't require any magnetic part, just electrostatic attraction.
 
  • #16
As a first approximation it sounds OK to me. Note, that it doesn't require any magnetic part, just electrostatic attraction.
I realise that now sorry, the guess at magnetic involvement was more a wild guess because the word spin was mentioned.
 
  • #17
DrDu
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So how does the electromagnetic force come into this explanation sorry, if that's the force responsible?
Of course it is. The attraction by the nuclei forms the basin in which the electrons are moving.
 

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