# Chemical Forums

## Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Q on July 05, 2021, 01:03:49 PM

Title: Crystals
Post by: Q on July 05, 2021, 01:03:49 PM
Experimentally it has been found that nickel has a density of 8,9 gcm-3 and that radius of its atom is 1,25 Å. Determine which type of cubic crystal lattice does nickel crystalize in.
________________________________
I don't know how to approach the problem because I cannot get a hang of how to calculate side of the unit cell. I know that it cannot possibly be cP (primitive) for the reason that the only metal that crystalizes in that crystal lattice is α-polonium. for that sake, it remains only cI or cF, but in both of these the relationship between radius and length of the side is differently expressed; cF: a=2√(2)r, cI: a=(4√(3)r)/(3)

Title: Re: Crystals
Post by: sjb on July 05, 2021, 03:26:22 PM
Have a look at, for instance, https://opentextbc.ca/chemistry/chapter/10-6-lattice-structures-in-crystalline-solids/
Title: Re: Crystals
Post by: Orcio_87 on July 05, 2021, 04:01:46 PM
How to calculate side of the unit cell ?

For cF (r - is the atom radius):

a = 2r √2

As of cI I think it will be:

a = 4r / √3
Title: Re: Crystals
Post by: Q on July 06, 2021, 04:54:06 AM
How to calculate side of the unit cell ?

For cF (r - is the atom radius):

a = 2r √2

As of cI I think it will be:

a = 4r / √3

I understand that, but I have to figure out which of these two unit cells does nickel crystalize in.
Title: Re: Crystals
Post by: Orcio_87 on July 06, 2021, 05:07:14 AM
Figuring out may be a bad way.

Did you considered calculating density of cI and cF unit cells and comparing it to the experimental data ?