Crystal Structure and Mechanical Properties
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Questions and Answers

What is the coordination number of the primitive cubic system?

  • 4
  • 12
  • 6 (correct)
  • 8

    • What is the formula for the atomic packing factor of the body-centred cubic system?

  • 0.74
  • 0.68 (correct)
  • 0.85
  • 0.52

    • What is the relationship between the cube edge length and the atomic radius in the body-centred cubic system?

  • a = 2R
  • a = R/√2
  • a = 2R/√3
  • a = 4R/√3 (correct)

    • What is the origin of the attractive part of the interatomic potential energy?

    <p>Pauli principle</p> Signup and view all the answers

    What is the unit of energy commonly used to describe atomic bonding?

    <p>Electron volt</p> Signup and view all the answers

    What is the potential energy of interatomic interaction dependent on?

    <p>Distance between atoms</p> Signup and view all the answers

    What is the formula for the energy of an electron moving through a potential difference of one volt?

    <p>E = q × V</p> Signup and view all the answers

    What is the value of the electron volt in joules?

    <p>1.6 x 10^-19 J</p> Signup and view all the answers

    Study Notes

    Crystal Structure

    • Atoms, ions, or molecules are spatially arranged in a crystal structure.
    • Crystal structure can be 2D or 3D.

    2D Crystalline Structure

    • Adjacent atoms form a unit cell.
    • Example of 2D crystalline structure is shown.

    3D Crystalline Structures

    Simple (Primitive) Cubic (SC)

    • Consists of one lattice point on each corner of the cube.
    • Each atom at a lattice point is shared equally between eight adjacent cubes.
    • Unit cell contains one atom (1/8 × 8).
    • Coordination number (nearest neighbor) is 6.

    Body-Centred Cubic (BCC)

    • Has one lattice point in the centre of the unit cell in addition to the eight corner points.
    • Net total of 2 lattice points per unit cell (1/8 × 8 + 1).
    • Examples: Cr, α-Fe, Mo.
    • Cube edge length, a = 4R/√3, R = a√3/4.
    • Atomic packing factor (APF) = 0.68.

    Face-Centred Cubic (FCC)

    • Examples: Cu, Al, Ag, Au.

    Interatomic Interaction

    • Repulsion between atoms is related to the Pauli principle.
    • Energy of the system increases abruptly when electronic clouds surrounding atoms start to overlap.
    • Attractive part of the potential energy curve dominates at large distances.

    Potential Energy of Interatomic Interaction

    • Can be calculated from the potential energy curve.
    • Depends only on the distance between the two atoms, U(r12).

    Energy Units

    • Electron volt (eV) is a convenient unit for atomic bonding.
    • Defined as the energy lost or gained by an electron when taken through a potential difference of one volt.
    • 1 eV = 1.6 × 10^-19 J.

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    Description

    This quiz covers the effect of bounding energy on mechanical and physical properties, such as melting temperature and thermal expansion, as well as crystal structures, including 2D and 3D crystalline structures.

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