The no. of atoms per unit cell in B.C.C. & F.C.C. is respectively -
B.C.C - Points are at corners and one in the centre of the unit cell.
Number of atoms per unit cell = 8 x 18 + 1 = 2.
F.C.C - Points are at the corners and also centre of the six faces of each cell.
Number of atoms per unit cell = 8 x 18 + 6 x 12 = 4.
How many unit cells are present in a cube-shaped ideal crystal of NaCl of mass 1.00 g? [Atomic masses: Na = 23, Cl = 35.5]
Mass (m) = density x volume = 1 g
Mol wt of NaCl = 58.5 g
Number of unit cell present in a cube shaped crystal of NaCl of mass 1 g = m x Na / (M x Z)
In NaCl each unit cell has 4 NaCl units.
Z = 4
What type of crystal defect is indicated in the diagram below ?
Here the crystal defect is the paired vacancies caused by the ions missing from their lattice sites.
An ionic compound has a unit cell consisting of A ions at the corners of a cube and B ions on the centres of the faces of the cube. The empirical formula for this compound would be
Unit cell consists of A ions at the corners is 8. So we know that the
contribution of corner is = 1/8th of corner = 1/8 x 8 = 1.
Unit cell consists of B ions at the centre of the six faces
Face = 1/2th of face
= 1/2 x 6= 3
So the empirical formula for this compound will be AB3
Copper crystallizes in fcc with a unit cell length of 361 pm. What is the radius of copper atom?
Radius of the atom = a ÷ a√2
In a compound, atoms of element Y form ccp lattice and those of element X occupy 2/3rd of tetrahedral voids. The formula of the compound will be -
No. of Y atoms per unit cell in ccp lattice = 4
No. of tetrahedral voids = 2 × 4 = 8
No. of tetrahedral voids occupied by X = 2/3 × 8 = 16/3
Therefore, Formula of the compound = X16/3Y4
= X4 Y3
Copper crystallises in fcc with a unit cell length of 361 pm. What is the radius of copper atom?