PLEASE HELP - Unit 2 Edexcel Chem GCE Past Paper Questions

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dogs4eva7
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Okay I don't understand why it's C?


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For 3, the answer's D but I don't understand why
For 4, it's D but I put A... I don't get the dipole-dipole interactions?? What's the difference?
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Pigster
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Bond angle around C with four bonds = 109.5, bond angle around O with two bonds = 104.5. Hence C.

For 3, Cl2 doesn't have polar bonds, the other three do, but CCl4 is symmetrical so the dipoles cancel out, hence overall non-polar (with polar bonds).

For 4, similar to 3, CH4 has polar bonds, but the dipoles cancel out so VdW only. B&C have hydrogen bonds since H is attached to N,O or F. HI doesn't have hydrogen bonding but has permanent dipoles.
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dogs4eva7
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(Original post by Pigster)
Bond angle around C with four bonds = 109.5, bond angle around O with two bonds = 104.5. Hence C.

For 3, Cl2 doesn't have polar bonds, the other three do, but CCl4 is symmetrical so the dipoles cancel out, hence overall non-polar (with polar bonds).

For 4, similar to 3, CH4 has polar bonds, but the dipoles cancel out so VdW only. B&C have hydrogen bonds since H is attached to N,O or F. HI doesn't have hydrogen bonding but has permanent dipoles.
For 3, is Cl2 not polar because it's symmetrical?
And what do you mean by permanent dipoles? I keep getting confused

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Why D for above?
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Physika
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Cl2 is non polar because it is a diatomic molecule meaning the constituent atoms have the same electronegativity and therefore no shift of electron density.


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Physika
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CCL4 is symmetrical so the dipoles cancel each other out and overall the molecule is non polar however there are still polar bonds.


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Physika
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Hydrogen bonds form in compound with hydrogen bonded to (N/O/F) only. Therefore HI is the the only one with a polar bond without hydrogen bonds


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dogs4eva7
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(Original post by Physika)
CCL4 is symmetrical so the dipoles cancel each other out and overall the molecule is non polar however there are still polar bonds.


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Thank you for your replies!
But what is a dipole? Like what does it mean? What's the difference between dipole-dipole and hydrogen bonding?
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Pigster
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Dipoles happen when two atoms with different electronegativities share their bonding pair electrons unevenly. The atom that gets more of the share has a small negative charge (not a full ionic charge), the other atom gets a small positive. These small + and - attract each other.

Hydrogen bonds are similar except the lone pair on a very electronegative atom (N, O or F) attracts a hydrogen on another molecule (which will have a small positive on it).
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Physika
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Size:  133.0 KB so the dipole dipole force come when to polar molecule come close and the positive and negative regions are attracted to each other making and intermolecular fore (a force holding molecules together without actually bonding them)


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Pigster
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Bingo.
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