# lattice

Discussion in 'Chemistry' started by rohIT, Feb 19, 2013.

1. ### rohITRegistered Senior Member

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76
the co-ordination number and the lattice of a salt is determined by the Rc/Ra ratio where Rc is the radius of cation and Ra is the radius of anion. this ratio is always less than one.
but what about metal hydrides? how is the lattice of a metal hydride? i mean shouldnt the ratio be more than one here?

3. ### originTrump is the best argument against a democracy.Valued Senior Member

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9,993
Well in the metal halide $AlH_3$ the Al certainly is larger than the 3 hydrogens so I guess the ratio is higher than 1.

5. ### NasorValued Senior Member

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6,221
Who told you that? It's not always less than 1. Its *usually* is less than 1, but there are plenty of examples where it isn't. Metal hydrides are one example, as you said. Another random example would be thallium fluoride.

7. ### rohITRegistered Senior Member

Messages:
76
nobody told me as such, but my book listed only the examples of the less than 1 category.
can you give me some references where their lattice structures n other details are mentioned?
thanks