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Why covalent bonds produce electricity?


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4 minutes ago, A_curious_Homosapien said:

Since the shared electron in the covalent bond oscillates from one atom to another, its should change the magnetic fields around it and hence result in formation of electricity. But why it doesn't happen?

It's not a classical oscillation, similar to how the orbitals of an atom are not defined orbits and thus do not radiate.

The electron is shared but there is no defined trajectory, per quantum mechanics.

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26 minutes ago, A_curious_Homosapien said:

Since the shared electron in the covalent bond oscillates from one atom to another, its should change the magnetic fields around it and hence result in formation of electricity. But why it doesn't happen?

Electricity requires a flow of electrons through a material. The electrons in covalently bound molecules are generally not free to flow throughout the structure, so no conduction of electricity occurs. (There can be exceptions, notably graphite, in which the π-orbitals of the fused rings of carbon merge to form a conduction band, allowing the electrons in those orbitals to flow.)  

As for magnetic properties, yes, electrons can create magnetic fields, due to their intrinsic angular momentum and sometimes also due to orbital angular momentum, if they are in orbitals that have this - many do not. But simple creation of a magnetic field does not imply that electricity is generated.

Edited by exchemist
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2 hours ago, A_curious_Homosapien said:

I request elaboration for this specific statement.

Permanent magnets do not rely on current flow to create a magnetic field. The magnetic moment of an electron arises from its intrinsic angular momentum (i.e. spin), as exchemist has already noted

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4 hours ago, A_curious_Homosapien said:

I request elaboration for this specific statement.

A changing magnetic field will classically induce an EMF. If a conductor is available, a current may then flow.

But in the case of an electron in a molecular orbital,  (i) this does not produce a changing magnetic field and (ii), as I've pointed out, there is no conductor if the bonding is covalent. 

Edited by exchemist
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On 10/12/2021 at 3:28 PM, A_curious_Homosapien said:

Since the shared electron in the covalent bond oscillates from one atom to another, its should change the magnetic fields around it and hence result in formation of electricity. But why it doesn't happen?

I should start by understanding covalent bonds.

Firstly there is not one shared electron in a covalent bond but two.

Secondly these two electrons do not oscillate from one atom to the other.

In truth, once bonded there are no 'atoms' in a covalently bonded molecule.

 

 

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16 hours ago, exchemist said:

A changing magnetic field will classically induce an EMF. If a conductor is available, a current may then flow.

But in the case of an electron in a molecular orbital,  (i) this does not produce a changing magnetic field and (ii), as I've pointed out, there is no conductor if the bonding is covalent. 

Ooh, now I got it. But what about exception like graphite?

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1 hour ago, A_curious_Homosapien said:

Ooh, now I got it. But what about exception like graphite?

Well I have not got it.

Are we talking about electric or magnetic effects of covalent bonds ?

These are quite separate and due to separate mechanisms.

Many substances that are covalently bonded conduct electricity, due to electrons being able to reach the conduction bands.

OLEPS are a good example.

 

There is a type of covalent bond called a dative bond which enjoys magnetic effects due to the separation of charge.

 

Please clarify which we are talking about, magnetic or electric effects as each deserve a thread of their own.

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1 hour ago, A_curious_Homosapien said:

Ooh, now I got it. But what about exception like graphite?

The exception in that case is due to the electrons in the π-bonds.

To go back a step, benzene is often drawn with 6 carbon atoms in a ring, with alternating single and double bonds (the Kekulé structure). But actually that is misleading. All 6 bonds are identical. You can consider each of the 6 atoms as sp2 hybridised, i.e. forming 3 σ-bonds at 120deg to one another, 2 to neighbouring carbons and one to hydrogen. That leaves one electron per atom in a p-orbital, perpendicular to the plane of the ring. These p-orbitals overlap with their neighbours to form a delocalised system, all the way round the ring. You can see this in the anomalous magnetic properties of benzene and other so-called aromatic molecules with this type of structure. You can generate a "ring current", causing the electrons to flow round the ring and create a magnetic field. https://en.wikipedia.org/wiki/Aromatic_ring_current

The same is true of fused aromatic rings, e.g like the ones in the diagram below:

image.png.5668959f28a6f6bfb28835720b89f63c.png

 

Graphite is what you get if you have an effectively infinite set of these fused rings, forming a sheet (like chickenwire), with successive sheets of rings stacked on top of each other. The bonding between sheets is only weak van der Waals attraction. This is why graphite is slippery (it has applications as a solid lubricant).

Regarding conduction of electricity (and heat*) what you end up with is a metal-like situation, with a "sea" of delocalised electrons, able to move across the sheet of rings freely. The difference from a metal is that the electrons are confined to one plane. They cannot easily jump from one sheet to the next. But along the plane of the rings you have metallic behaviour. 

 

*Graphite is used for the heat shields of spacecraft, as it conducts heat well along the planes, but very poorly between one and the next. So it is ideal!

 

49 minutes ago, studiot said:

Well I have not got it.

Are we talking about electric or magnetic effects of covalent bonds ?

These are quite separate and due to separate mechanisms.

Many substances that are covalently bonded conduct electricity, due to electrons being able to reach the conduction bands.

OLEPS are a good example.

 

There is a type of covalent bond called a dative bond which enjoys magnetic effects due to the separation of charge.

 

Please clarify which we are talking about, magnetic or electric effects as each deserve a thread of their own.

OLEPS? Wot dey? 

Edited by exchemist
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13 minutes ago, studiot said:

Organic light emitting polymers.

PS I fully support your other efforts here. +1

OK. These seem to be linear analogues of the planar conducting structure I was describing in graphite: https://www.sigmaaldrich.com/GB/en/technical-documents/technical-article/materials-science-and-engineering/organic-electronics/light-emitting-polymers i.e. long 1D chains of conjugated aromatic rings, built up from dye molecules, rather than 2D sheets. 

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On 10/21/2021 at 6:35 PM, studiot said:

Are we talking about electric or magnetic effects of covalent bonds ?

Actually we are talking about why magnetic field are not induced in covalent bonds.

On 10/21/2021 at 6:40 PM, exchemist said:

The exception in that case is due to the electrons in the π-bonds.

To go back a step, benzene is often drawn with 6 carbon atoms in a ring, with alternating single and double bonds (the Kekulé structure). But actually that is misleading. All 6 bonds are identical. You can consider each of the 6 atoms as sp2 hybridised, i.e. forming 3 σ-bonds at 120deg to one another, 2 to neighbouring carbons and one to hydrogen. That leaves one electron per atom in a p-orbital, perpendicular to the plane of the ring. These p-orbitals overlap with their neighbours to form a delocalised system, all the way round the ring. You can see this in the anomalous magnetic properties of benzene and other so-called aromatic molecules with this type of structure. You can generate a "ring current", causing the electrons to flow round the ring and create a magnetic field. https://en.wikipedia.org/wiki/Aromatic_ring_current

The same is true of fused aromatic rings, e.g like the ones in the diagram below:

image.png.5668959f28a6f6bfb28835720b89f63c.png

 

Graphite is what you get if you have an effectively infinite set of these fused rings, forming a sheet (like chickenwire), with successive sheets of rings stacked on top of each other. The bonding between sheets is only weak van der Waals attraction. This is why graphite is slippery (it has applications as a solid lubricant).

Regarding conduction of electricity (and heat*) what you end up with is a metal-like situation, with a "sea" of delocalised electrons, able to move across the sheet of rings freely. The difference from a metal is that the electrons are confined to one plane. They cannot easily jump from one sheet to the next. But along the plane of the rings you have metallic behaviour. 

 

*Graphite is used for the heat shields of spacecraft, as it conducts heat well along the planes, but very poorly between one and the next. So it is ideal!

 

OLEPS? Wot dey? 

I am sorry friends, I think I lost it from here. It's not your explanation, it's just my weak grasp in chemistry, I am trying my best to improve. But alot of thanks for your effort. Will take my teacher's help in this.

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19 hours ago, A_curious_Homosapien said:

Actually we are talking about why magnetic field are not induced in covalent bonds.

I am sorry friends, I think I lost it from here. It's not your explanation, it's just my weak grasp in chemistry, I am trying my best to improve. But alot of thanks for your effort. Will take my teacher's help in this.

OK sorry if this was a bit too much.

Just take away the message that the bonding in graphite is partly covalent and in effect partly metallic along the planes, so that is why it can conduct heat and electricity along the planes.

Exception to rules are what make a subject fun, but they can be confusing to the beginner. 

Edited by exchemist
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