Chemical Forums

Specialty Chemistry Forums => Biochemistry and Chemical Biology Forum => Topic started by: Luna101 on February 16, 2021, 07:06:08 PM

Title: Crystalline Solids
Post by: Luna101 on February 16, 2021, 07:06:08 PM

Hi please help me sketch the unit cell, determine the lattice shape and the number of “atoms” in the unit cell in the picture. Thanks in advance!

Title: Re: Crystalline Solids
Post by: Babcock_Hall on February 16, 2021, 08:25:24 PM

Would you show us your attempts?  A good place to start is by defining what a unit cell is.

Title: Re: Crystalline Solids
Post by: Luna101 on February 16, 2021, 08:35:32 PM

I did the regular shapes like cube, Triangles and rectangle but the patterns I don't know where to start

Title: Re: Crystalline Solids
Post by: Babcock_Hall on February 17, 2021, 10:09:23 AM

Start with the definition of a unit cell, and apply it to each example.  In problems such as these there is typically more than one right answer.

Title: Re: Crystalline Solids
Post by: Luna101 on February 17, 2021, 10:13:12 AM

Ok can you please show me at least an example from the patterns??

Title: Re: Crystalline Solids
Post by: AWK on February 17, 2021, 10:42:48 AM

You have to find unit cells of two-dimensional space groups (or the bases of parallelepipeds of three-dimensional groups)
The base of a unit cell can be as small as possible a square, rectangle, rhombus, or parallelogram. It is often possible to select another cell with the same area (two-dimensional).
Search your crystallography textbook for plane symmetry group (s) or Wikipedia for Wallpaper group (very complex explanation).

Title: Re: Crystalline Solids
Post by: Luna101 on February 17, 2021, 12:47:47 PM

Please please just do one example from the picture so I can refer to it when I do the other problems please

Title: Re: Crystalline Solids
Post by: AWK on February 17, 2021, 02:15:53 PM

Look at the layer of the NaCl structure closest to you. Does that remind you of anything?

Title: Re: Crystalline Solids
Post by: Luna101 on February 17, 2021, 02:23:17 PM

Is is supposed to represent pattern #2 or #4?

Title: Re: Crystalline Solids
Post by: AWK on February 17, 2021, 02:46:50 PM

Patern 2 has identical elements!

Title: Re: Crystalline Solids
Post by: Luna101 on February 17, 2021, 02:48:17 PM

Oh ok thanks. I figure out pattern 3 and 4 but I’m not sure about pattern 1,5,6

Title: Re: Crystalline Solids
Post by: Luna101 on February 17, 2021, 08:48:25 PM

Never mind I figured it out