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Problem: Calcium sulfide adopts the sodium chloride crystal structure (figure below). How many S 2− ions are in the CaS unit cell?

FREE Expert Solution

NaCl crystal  face centered cubic (FCC) 

  • FCC one atom/ion per corner, one atom/ion at each face
  • S2-
    • 8 corner ions (1/8 contribution) 
    • 6 face ions (1/2 contribution) 


S2- ions per unit cell:


# of ions=(18)8+(12)6

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Problem Details

Calcium sulfide adopts the sodium chloride crystal structure (figure below). How many S 2− ions are in the CaS unit cell?

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Based on our data, we think this problem is relevant for Professor Gaines' class at SPELMAN.

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Our data indicates that this problem or a close variation was asked in Chemistry: The Molecular Nature of Matter and Change - Silberberg 8th Edition. You can also practice Chemistry: The Molecular Nature of Matter and Change - Silberberg 8th Edition practice problems.