Gold (atomic mass 197 u) crystallises in a face-centred unit cell. Wha...
Given,
Edge length of the Gold unit cell (a) = 0.407 x 10-7m
For FCC unit cell, the atomic radius (r) = a/(2√2)
= 0.407 x 10-9/(2√2)
= 0.144 nm.
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Gold (atomic mass 197 u) crystallises in a face-centred unit cell. Wha...
Given:
- Atomic mass of gold = 197 u
- Edge length of the gold unit cell = 0.407 x 10^(-9) m
To find:
The atomic radius of gold.
Solution:
The face-centered unit cell of gold consists of atoms located at the corners and the face centers of the unit cell.
Step 1: Calculate the number of atoms in the unit cell:
In a face-centered unit cell, there are:
- 8 corner atoms, where each atom contributes 1/8th to the unit cell
- 6 face-centered atoms, where each atom contributes 1/2 to the unit cell
Total number of atoms in the unit cell = (8 x 1/8) + (6 x 1/2) = 4
Step 2: Calculate the volume of the unit cell:
The volume of a unit cell can be calculated using the formula:
Volume = (edge length)^3
Given:
Edge length of the unit cell = 0.407 x 10^(-9) m
Volume of the unit cell = (0.407 x 10^(-9))^3 = 6.835 x 10^(-29) m^3
Step 3: Calculate the volume occupied by each atom:
Since there are 4 atoms in the unit cell, the volume occupied by each atom can be calculated by dividing the total volume of the unit cell by the number of atoms:
Volume occupied by each atom = Volume of unit cell / Number of atoms = 6.835 x 10^(-29) / 4 = 1.70875 x 10^(-29) m^3
Step 4: Calculate the radius of each atom:
The volume occupied by each atom can also be calculated using the formula for the volume of a sphere:
Volume of a sphere = (4/3) x π x (radius)^3
Given:
Mass of gold atom = 197 u
Avogadro's number = 6.022 x 10^23
The mass of one gold atom can be converted to grams:
Mass of one gold atom = (197 u) x (1.66 x 10^(-27) kg/u) = 3.26 x 10^(-25) kg
The volume occupied by one gold atom can be calculated using its mass and the density of gold:
Density of gold = Mass / Volume
Volume = Mass / Density = (3.26 x 10^(-25) kg) / (19.3 x 10^3 kg/m^3) = 1.69 x 10^(-29) m^3
Equating the two expressions for the volume occupied by each atom:
1.70875 x 10^(-29) m^3 = (4/3) x π x (radius)^3
Simplifying the equation:
(radius)^3 = (1.70875 x 10^(-29) m^3) x (3/4π)
(radius)^3 = 3.226 x 10^(-29) m^3
Taking the cube root of both sides:
radius = (3.226 x 10^(-29))^(1/3) m
radius ≈
Gold (atomic mass 197 u) crystallises in a face-centred unit cell. Wha...
Given,
Edge length of the Gold unit cell (a) = 0.407 x 10-7m
For FCC unit cell, the atomic radius (r) = a/(2√2)
= 0.407 x 10-9/(2√2)
= 0.144 nm.