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Topic: Unit Cell Side Length?  (Read 6259 times)

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Offline mickfortis

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Unit Cell Side Length?
« on: January 02, 2011, 07:12:37 AM »
I'm currently doing a chemistry lab report about Avogadro's Number and am having trouble answering 2 questions...
The first one is "Find the side length of the Unit Cell of the crystalline structure of Iron and Aluminium3
The second: "Find the number of atoms present in one unit cell of each of the crystalline structures"
Ive searched on the internet but havent found anything ???
your help is appreciated

Offline mickfortis

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Re: Unit Cell Side Length?
« Reply #1 on: January 02, 2011, 09:24:58 AM »
Somebody please answer.... I need to know the answers to these questions.

Offline mickfortis

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Re: Unit Cell Side Length?
« Reply #2 on: January 02, 2011, 10:59:15 AM »
Some helpful people here huh.... ::)

Offline sjb

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Re: Unit Cell Side Length?
« Reply #3 on: January 02, 2011, 11:13:36 AM »
Some helpful people here huh.... ::)
Bear in mind it's a Sunday, for one.

If you're doing this in terms of Avogadro's number, there may be a more useful way around this, but does http://www.google.co.uk/search?q=iron+crystal+structure help?

Offline Borek

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Re: Unit Cell Side Length?
« Reply #4 on: January 02, 2011, 11:33:07 AM »
Start with the density, calculate volume of a single cell (that's where Avogadro's number comes in handy), assume it is just a cube and calculate length of the edge. Not exact but better than nothing.
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Offline mickfortis

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Re: Unit Cell Side Length?
« Reply #5 on: January 02, 2011, 12:45:27 PM »
Some helpful people here huh.... ::)
Bear in mind it's a Sunday, for one.

If you're doing this in terms of Avogadro's number, there may be a more useful way around this, but does http://www.google.co.uk/search?q=iron+crystal+structure help?

Thanks for your help man! Much appreciated.
I assume the "cell parameters" (a,b,c) in the first link of that google search correspond to the side length i am looking for?

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Re: Unit Cell Side Length?
« Reply #6 on: January 05, 2011, 03:32:42 PM »
To solve this problem with density and the nature of the element as givens, you need to know the number of atoms contained in a unit cell. Fe has a bcc structure, therefore there are two Fe atoms per unit cell. Al, on the other hand, has a ccp structure and therefore a unit cell of Al has four atoms. Now you can use the molar masses, density, avogadro's number to find the volume of the unit cell, and root 3 will give you the edge-length of the cube. Therefore proceed as follows

Volume of unit cell= g/cm3 x mol/g x Avogadros number of atoms/mol x unit cell volume/number of atoms in unit cell

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