I need help with the bottom portion (radius-ratio rule), here is the table they

Question

I need help with the bottom portion (radius-ratio rule), here is the table they refer to:

This is involving crystals. NaCI Crystal Number of Cl ions in the unit cell (FCC) % Cr), (e) + shared by shared by (e), ( (l.) x 6 Number of Na" ions on edges of ell Number of Na" ions on edges of cell-i.. shared by 12 -, cell(s) Number of Na+ ions in center of cell cells) Total number of Na" ions in unit cell Radius-ratio rule (necessary data is in Table 16.1, at the start of the data pages) Observed structure NaCI Observed structure ZnS Observed structure-csC KI TrPredicted structure CuBr rlr Predicted structure TIBr Predicted structure Report on unknown

Explanation / Answer

Radius ratio is given by r+/r- where r+ is the radius of the cation and r- is the radius of the anion.

if r+/r- is between 0.414 - 0.732, 6:6 (NaCl lattice)

if r+/r- is >0.732, 8:8 (CsCl) is predicted to be more stable.

KI

R+/r- = 0.133/ 0.216= 0.616

CuBr

R+/r- = 0.096/ 0.195= 0.492

TlBr

R+/r- = 0.147/ 0.195= 0.754

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