The Student Room Group

Halogens

Why does Cl- ions form stronger bonds than Br- and Br- forms steonger bonds than I-?
Reply 1
Original post by Ellie.Ginger
Why does Cl- ions form stronger bonds than Br- and Br- forms stronger bonds than I-?


https://en.wikipedia.org/wiki/Coulomb%27s_law

Cl- is smaller than Br- (ditto than I-). r (in the above law) is smaller and hence F is larger, i.e. the bond is stronger.

In general, smaller ions can snuggle up closer together and therefore form stronger bonds. Also important, though, is the charge on the ion (q), but in the case of halides, they are all -1.
Original post by Pigster
https://en.wikipedia.org/wiki/Coulomb%27s_law

Cl- is smaller than Br- (ditto than I-). r (in the above law) is smaller and hence F is larger, i.e. the bond is stronger.

In general, smaller ions can snuggle up closer together and therefore form stronger bonds. Also important, though, is the charge on the ion (q), but in the case of halides, they are all -1.


Thank you so muchhh
Smaller ions with the same charge have less shielding due to having fewer electron shells and so have a greater charge density. This means the force of attraction between a smaller negative ion (Cl- compared to Br-) and neighbouring positive ions (Na+ for example) is greater which results in higher melting point and lattice enthalpy.
Reply 4
Original post by Madasahatter
...have less shielding due to having fewer electron shells...

This would be true if an ionic bond involved the attraction between nuclei of +ve ions and the -ve ions, but it is the entire +ve ion that is doing the attracting.
Original post by Pigster
This would be true if an ionic bond involved the attraction between nuclei of +ve ions and the -ve ions, but it is the entire +ve ion that is doing the attracting.


If the +ve ion is the same, the attraction from the nucleus of a smaller -ve ion to the electrons of the +ve ions will be greater due to the nucleus of the -ve ion being closer and less shielded.

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