Sasha Shasha
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How to know the shape of the molecule is symmetrical or asymmrtrical ?
To identify whether is polar or non polar molecules
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Pigster
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(Original post by Sasha Shasha)
How to know the shape of the molecule is symmetrical or asymmrtrical ?
To identify whether is polar or non polar molecules
Which spec are you doing?
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Sasha Shasha
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(Original post by Pigster)
Which spec are you doing?
For example, a molecule of carbon dioxide has two carbon—oxygen bonds that are polar due to the electronegativity difference between the carbon and oxygen atoms.
But it has no net dipole moment because its symmetrical
Dipoles cancel out , why and how ? How to know which one is symmetrical
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Kian Stevens
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(Original post by Sasha Shasha)
For example, a molecule of carbon dioxide has two carbon—oxygen bonds that are polar due to the electronegativity difference between the carbon and oxygen atoms.
But it has no net dipole moment because its symmetrical
Dipoles cancel out , why and how ? How to know which one is symmetrical
Determining whether something is symmetrical or not is quite simple, and I assume you can do this

Electronegativity is the ability of an atom to attract electrons in a covalent bond; let’s just call this the ‘pull’ of electrons
If you consider that in a carbon dioxide molecule both C=O bonds are of the same electronegativity, then the ‘pull’ of electrons on one side of the molecule is the same as the ‘pull’ of electrons on the other side of the molecule
Therefore the dipoles cancel out because on both sides of the molecule, there’s no overall ‘pull’ of electrons, and so there’s no net dipole
This is due to the molecule being symmetrical, i.e. quite simply, one side of the molecule is identical to the other side, and thus both sides will counteract each other

If you were to take an asymmetrical molecule, you’d see that it does have a net dipole, for reasons opposite to above
Consider the following simple molecules: methane, chloromethane, dichloromethane, trichloromethane and tetrachloromethane
If you have a quick search on Wikipedia for these molecules, you’ll see that the dipole moments of them change with how symmetrical they are; this is such that methane and tetrachloromethane have no dipole moment, as they are completely symmetrical
Last edited by Kian Stevens; 1 month ago
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(Original post by Sasha Shasha)
For example, a molecule of carbon dioxide has two carbon—oxygen bonds that are polar due to the electronegativity difference between the carbon and oxygen atoms.
But it has no net dipole moment because its symmetrical
Dipoles cancel out , why and how ? How to know which one is symmetrical
Depening on which exam board you do, there are shortcuts.
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Sasha Shasha
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(Original post by Kian Stevens)
Determining whether something is symmetrical or not is quite simple, and I assume you can do this

Electronegativity is the ability of an atom to attract electrons in a covalent bond; let’s just call this the ‘pull’ of electrons
If you consider that in a carbon dioxide molecule both C=O bonds are of the same electronegativity, then the ‘pull’ of electrons on one side of the molecule is the same as the ‘pull’ of electrons on the other side of the molecule
Therefore the dipoles cancel out because on both sides of the molecule, there’s no overall ‘pull’ of electrons, and so there’s no net dipole
This is due to the molecule being symmetrical, i.e. quite simply, one side of the molecule is identical to the other side, and thus both sides will counteract each other

If you were to take an asymmetrical molecule, you’d see that it does have a net dipole, for reasons opposite to above
Consider the following simple molecules: methane, chloromethane, dichloromethane, trichloromethane and tetrachloromethane
If you have a quick search on Wikipedia for these molecules, you’ll see that the dipole moments of them change with how symmetrical they are; this is such that methane and tetrachloromethane have no dipole moment, as they are completely symmetrical
But carbon dioxide molecule both C=O bonds are of the different electronegativity
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Sasha Shasha
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(Original post by Pigster)
Depening on which exam board you do, there are shortcuts.
A level
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(Original post by Sasha Shasha)
A level
OCR A/B? Edexcel? AQA? etc.
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Sasha Shasha
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(Original post by Pigster)
OCR A/B? Edexcel? AQA? etc.
CIE
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Carbon dioxide is a linear molecule, so the pull of electrons from one C=O bond is directly opposed by that of the other C=O bond. This means that the molecule is symmetrical, and hence the opposing pulls cancel out and the strongest intermolecukar force possible is only induced dipole/Van der Waals forces.

To find out the shape of a molecule, use VSEPR rules, or sometimes it can just be drawn out in displayed formula.
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(Original post by Sasha Shasha)
CIE
According to the examples on your spec, if a molecule has no lone pairs, then it will be symmetrical, the dipoles will cancel out and it will be non-polar.

If it has lone pairs, they won't and it won't.
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Kian Stevens
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(Original post by Pigster)
According to the examples on your spec, if a molecule has no lone pairs, then it will be symmetrical, the dipoles will cancel out and it will be non-polar.

If it has lone pairs, they won't and it won't.
For clarity, I assume you mean that the central atom has no lone pairs, not the molecule itself?
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(Original post by Kian Stevens)
For clarity, I assume you mean that the central atom has no lone pairs, not the molecule itself?
Good point, that's exactly what I meant - CO2 has no lp on the central C, but the lp on each of the O atoms have no effect on the shape around the C.
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Sasha Shasha
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(Original post by Pigster)
Good point, that's exactly what I meant - CO2 has no lp on the central C, but the lp on each of the O atoms have no effect on the shape around the C.
How about in Cis trans isomerism ? Why trans isomer is more symmetrical
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