Halogens a level chem

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Tanyme
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If Halogens are non-polar, then what causes an induced dipole in Halogens that holds the molecule together?
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j25_8
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(Original post by Tanyme)
If Halogens are non-polar, then what causes an induced dipole in Halogens that holds the molecule together?
I haven’t done chemistry in a long time but I believe it’s this:

• Non polar molecules will still be held together by induced dipole - dipole intermolecular forces

• electrons aren’t static so they can potentially be concentrated at random points in a specific part of the atom they orbit because they’re always moving (you can google search for an “Electron Cloud” for a depiction of this)

• so when they’re moving around, there is a chance for every molecule to have a concentrated, uneven amount of electrons on any of the molecule’s sides which gives it a temporary (or induced) dipole.

• This differs from permanent dp - dp forces because with permanent dp dp forces, there is *always* a positive and negative dipole (eg in CH3F) due to either a difference in electronegativity of the atoms in the molecule, or the shape of the molecule (or oftentimes both). Induced dipole dipole forces don’t rely on permanent dipoles to hold molecules together though, and are instead random in occurance due the random positioning of electrons in an electron cloud

- They are also different from hydrogen bonds because hydrogen bonds form as a result of a polar hydrogen being very strongly attracted to a lone *pair* of electrons in another molecule. This is different from induced dipole dipole forces because hydrogen bonds require a polar molecule consisting of at least a hydrogen atom and any atom with a lone pair of electrons for the hydrogen to form a hydrogen bond with. Induced dipole dipole forces do not occur between permanent dipoles though (and every molecule that can form hydrogen bonds has to be polar btw, because hydrogen always forms a slightly positive dipole whenever it creates a polar molecule, and polar molecules always have permanent dipoles), so they are different in nature

Here’s a graphic i found that was quite good. What you see in this picture occurs to every halogen molecule. Hope this helps

https://images.app.goo.gl/Dw4dvMoByD5zdZQz9
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scimus63
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There will be Van der Waals bonding between the halogen molecules, have a look here:
https://science-revision.co.uk/A-lev...s_bonding.html
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kaorimiyazono
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Careful with your wording: the covalent bond holds the two atoms in the molecule together (because halogens are diatomic and go around in pairs e.g. Cl2, Br2 etc).
There are Van der Waal forces between the molecules though.
Van der Waal forces are present in all molecules because atoms have clouds of electrons which move around the nucleus and cause induced dipoles (which constantly change as the electrons move around) when there's a higher concentration of electrons on one side of the atom. This causes the atom to have one side be delta negative (partially negative due to the higher electron concentration) and one side to be delta positive (partially positive due to the lower electron concentration). When atoms get close enough together, these induced dipoles mean that they are attracted to each other. This is what happens between halogen molecules.
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charco
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(Original post by kaorimiyazono)
Careful with your wording: the covalent bond holds the two atoms in the molecule together (because halogens are diatomic and go around in pairs e.g. Cl2, Br2 etc).
There are Van der Waal forces between the molecules though.
Van der Waal forces are present in all molecules because atoms have clouds of electrons which move around the nucleus and cause induced dipoles (which constantly change as the electrons move around) when there's a higher concentration of electrons on one side of the atom. This causes the atom to have one side be delta negative (partially negative due to the higher electron concentration) and one side to be delta positive (partially positive due to the lower electron concentration). When atoms get close enough together, these induced dipoles mean that they are attracted to each other. This is what happens between halogen molecules.
Be careful with the term Van der Waals forces.

By definition these cover both induced temporary dipole and permanent dipole interactions.

There are some boards that require students to know this.


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kaorimiyazono
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(Original post by charco)
Be careful with the term Van der Waals forces.

By definition these cover both induced temporary dipole and permanent dipole interactions.

There are some boards that require students to know this.


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Ohh no you're right sorry I didn't realise that you needed to know this at A-Level. I did AQA and the mark schemes allowed us to use Van der Waals when referring to induced temporary dipole interactions while permanent dipole interactions were either "permanent dipole" or "dipole-dipole". Thank you for pointing that out.
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