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Q.1. The total number of atoms in one unit cell of face-centered unit cubic cell is ______ atoms.
(a) 2
(b) 6
(c) 4
(d) 8

Correct Answer is Option (b)

In face-centered cubic unit cell, atoms are present at each of the corners and at the centre of the face of the cube.
8 corners × Number of Atoms in a Unit Cell | Physical Chemistryof an atom = 1
6 faces × Number of Atoms in a Unit Cell | Physical Chemistryof an atom = 3
Thus, the total number of atoms in face-centered cubic unit cell: 1+3=4 atoms.


Q.2. The total number of atoms in one unit cell of primitive unit cubic cell is ______ atom(s).
(a) 1
(b) 8
(c) 4
(d) 2

Correct Answer is Option (a)

In primitive cubic unit cell, atoms are present only at the corner of the cell. Thus, in actual, only Number of Atoms in a Unit Cell | Physical Chemistry of an atom (or ion or molecule) belongs to a particular unit cell. Hence, the total number of atoms in primitive cubic unit cell = 8 ×Number of Atoms in a Unit Cell | Physical Chemistry= 1 atom.


Q.3. The total number of atoms in one unit cell of body-centered unit cubic cell is ______ atoms.
(a) 4
(b) 3
(c) 8
(d) 2

Correct Answer is Option (d)

In body-centered cubic unit cell, one atom is present at each of the corners and one atom at its body center.
8 corners × Number of Atoms in a Unit Cell | Physical Chemistryof an atom = 1
1 body-centered atom
Thus, the total number of atoms in body-centered cubic unit cell: 1+1=2 atoms.

Q.4. In primitive unit cubic cell, only _______ of an atom (or ion or molecule) belongs to a particular unit cell.

(a)Number of Atoms in a Unit Cell | Physical Chemistry
(b)Number of Atoms in a Unit Cell | Physical Chemistry
(c)Number of Atoms in a Unit Cell | Physical Chemistry
(d) Number of Atoms in a Unit Cell | Physical Chemistry

Correct Answer is Option (c)

In primitive unit cubic cell, each atom at the corner is shared between 8 adjacent unit cells. Thus, only Number of Atoms in a Unit Cell | Physical Chemistryof an atom (or ion or molecule) belongs to a particular unit cell.

The document Number of Atoms in a Unit Cell | Physical Chemistry is a part of the Chemistry Course Physical Chemistry.
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FAQs on Number of Atoms in a Unit Cell - Physical Chemistry

1. How can I determine the number of atoms in a unit cell?
Ans. To determine the number of atoms in a unit cell, you need to know the type of crystal structure and the number of atoms associated with each lattice point. For example, in a simple cubic lattice, there is only one atom at each lattice point, so the number of atoms in the unit cell is equal to the number of lattice points.
2. What is the relationship between lattice points and atoms in a unit cell?
Ans. In a crystal lattice, lattice points are imaginary points that represent the positions of the atoms within the crystal structure. Each lattice point can correspond to one or multiple atoms depending on the crystal structure. For example, in a face-centered cubic (FCC) structure, each lattice point corresponds to four atoms.
3. How does the crystal structure affect the number of atoms in a unit cell?
Ans. The crystal structure determines the arrangement of atoms within a crystal lattice and, consequently, the number of atoms in a unit cell. Different crystal structures have different arrangements of lattice points, which can correspond to different numbers of atoms. For example, a body-centered cubic (BCC) structure has two atoms per unit cell, while a hexagonal close-packed (HCP) structure has six atoms per unit cell.
4. Can the number of atoms in a unit cell vary for the same crystal structure?
Ans. No, the number of atoms in a unit cell is fixed for a specific crystal structure. The arrangement of lattice points and the number of atoms associated with each lattice point are inherent properties of the crystal structure. Changing the number of atoms in a unit cell would require altering the crystal structure itself.
5. How does the number of atoms in a unit cell affect the properties of a material?
Ans. The number of atoms in a unit cell can significantly influence the physical properties of a material. It affects the density, thermal conductivity, electrical conductivity, and other material properties. Additionally, the arrangement of atoms within the unit cell determines the crystal's symmetry and can impact its mechanical, optical, and magnetic properties. Understanding the number of atoms in a unit cell helps in predicting and analyzing the behavior of materials in various applications.
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