See the image below..?

enter image source here

Please explain your answer.

1 Answer
Ernest Z.
Sep 24, 2016

The compound could be #"CaF"_2#.

Explanation:

The big atoms (#bb"B"#) are counted as:

  • 8 completely inside the cell = 8 × 1 atom = 8 atoms

The small atoms (#bb"A"#) are counted as:

  • 1 at each corner = 8 × ⅛ atom = 1 atom
  • 1 at each face = 6 × ½ atom = 3 atoms

Total = 4 #"A"# atoms.

The formula is #"B"_8"A"_4# or #"AB"_2#.

The formula must be either #"CaF"_2# or #"SO"_2#.

#"SO"_2# is a covalent compound. It would exist as discrete molecules in the unit cell.

Hence, the compound must be #"CaF"_2# (fluorite).

Here's a better picture of the fluorite unit cell, that makes it easier to count the atoms.

Fluorite unit cell
(From geologycafe.com)

Related questions
See all questions in Phases of Matter
Impact of this question
3066 views around the world
You can reuse this answer
Creative Commons License