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# how many formula units are in the unit cell shown for li2s?

The crystal structure of lithium sulfide (Li2S) is pictured here. (Intro 1 figure) The edge length of the unit cell is 5.88*10^2^2 pm.

i guess it is FCC ( face cenred cubic)

1–

What are the coordination numbers of and Li^+ and S^2- in the lithium sulfide crystal shown? Enter the values in order of Li^+ and S^2-, respectively.

Ans… i though it shld be 4,4 .. but it says ” Face ions are shared between two unit cells.”…

plz someone

2- How many formula units are in the unit cell shown for Li2S ?

Ans- i gues it shld be 1 but it says –
The formula represents one formula unit. How many sets of are in the unit cell?

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asked by Dr Bob plz help
Jan 24, 2009
I don’t have the book and can’t see the picture. I can’t find anything on the Internet so I’m passing on this one. I’ve also looked in all the references I have at home and can’t find anything on Li2S.

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posted by DrBob222
Jan 24, 2009
The Number of Formula Units is 4, but I don’t know why, I just happened to guess it and it marked it as correct for me.
As for part 1, I don’t know 🙁

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posted by Mrs C
Jan 25, 2009
It’s 4,8. Easy, you just count the lines, but note that the S(2-) is on the surface, so it’s surrounded by the Li+ of the adjacent unit cell as well as its own.

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posted by Dash
Jan 26, 2009
What is the density of Li2S in grams per cubic centimeter? this was the 3rd part of this question :/

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posted by Anonymous
Jan 27, 2009

The density of lithium sulfide is 1.5g/cm^3

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posted by friend
Jan 27, 2009
the number of formula units is 4: there are 4 Sulfur atoms in the unit cell (8* 1/8 + 6* 1/2) and 8 Lithium atoms (all contained within the unit cell)

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posted by SJ
Jan 27, 2012