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 ?

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?

for 2nd question ( shown for Li2S)

thnks

1. 4,8

2.4

4,8

2.=4

To determine the coordination numbers of Li^+ and S^2- in the lithium sulfide crystal shown, we need to understand the crystal structure. In this case, you correctly identified that lithium sulfide (Li2S) has a face-centered cubic (FCC) crystal structure.

1- The coordination number is the number of nearest neighbors surrounding an ion in a crystal lattice. In an FCC structure, each ion is surrounded by 12 nearest neighbors. However, it is important to note that Li2S has face ions that are shared between two unit cells. In other words, the ions on the faces of the unit cell are not fully contained within the unit cell and are instead shared with neighboring unit cells. This affects the coordination number.

For Li^+, since the Li ions are positioned within the unit cell corners, they are fully contained and not shared with neighboring unit cells. Therefore, each Li^+ ion has 8 nearest neighbors from the surrounding S^2- ions. So, the coordination number for Li^+ is 8.

For S^2-, since the S ions are positioned on the face centers, they are shared between the unit cell in question and its surrounding unit cells. This means that each S^2- ion contributes to the coordination number of the unit cell as well as the neighboring unit cells. As a result, each S^2- ion has 4 nearest neighbors from the S^2- ions in the unit cell itself and another 4 nearest neighbors from the S^2- ions in the neighboring unit cells. So, the coordination number for S^2- is 8.

Therefore, the correct coordination numbers for Li^+ and S^2- in the lithium sulfide crystal shown are 8 and 8, respectively.

2- The number of formula units in the unit cell can be determined by analyzing the composition of the compound and the arrangement of ions in the crystal lattice.

In the case of Li2S, the formula indicates that there are two lithium ions (Li^+) for every one sulfur ion (S^2-). Since the unit cell contains multiple ions, we need to consider how many sets of these ions are present.

From the crystal structure image you provided and the fact that Li2S has an FCC structure, we know that each corner of the unit cell contains a Li+ ion. This suggests that there are probably 8 total Li^+ ions in the unit cell (8 corners * 1 Li^+ per corner). Similarly, each face center of the unit cell contains an S^2- ion. This suggests that there are probably 6 total S^2- ions in the unit cell (6 face centers * 1 S^2- per face center).

Based on this information, we can deduce that there are 8 Li^+ ions and 6 S^2- ions in the unit cell of Li2S. Since the formula of Li2S represents one formula unit, the number of Li2S formula units in the unit cell is 1.

Therefore, the correct answer to the number of Li2S formula units in the unit cell shown is 1.