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Questions and Answers
The majority of stable elements are non-metallic.
The majority of stable elements are non-metallic.
False
There are 17 elements that have a face-centered cubic (FCC) structure.
There are 17 elements that have a face-centered cubic (FCC) structure.
True
BCC metals become more ductile at low temperatures.
BCC metals become more ductile at low temperatures.
False
The coordination number of BCC crystals is 8.
The coordination number of BCC crystals is 8.
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The HCP structure is considered a slip system that is close-packed.
The HCP structure is considered a slip system that is close-packed.
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FCC metals retain their ductility and toughness to absolute zero.
FCC metals retain their ductility and toughness to absolute zero.
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There are 21 elements that have a body-centered cubic (BCC) structure.
There are 21 elements that have a body-centered cubic (BCC) structure.
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The HCP structure is inelastic in nature.
The HCP structure is inelastic in nature.
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In a face-centered cubic (FCC) lattice, each atom is in contact with 8 neighbor atoms.
In a face-centered cubic (FCC) lattice, each atom is in contact with 8 neighbor atoms.
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The coordination number for the hexagonal lattice is 12.
The coordination number for the hexagonal lattice is 12.
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Atoms in corners of a crystal unit cell are shared with 1/4 within the cell.
Atoms in corners of a crystal unit cell are shared with 1/4 within the cell.
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The atomic packing factor (APF) for FCC and hexagonal close-packed structures is 0.74.
The atomic packing factor (APF) for FCC and hexagonal close-packed structures is 0.74.
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Aluminium is FCC, while iron is also FCC.
Aluminium is FCC, while iron is also FCC.
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Slip occurs on the most densely packed planes in a crystal.
Slip occurs on the most densely packed planes in a crystal.
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The number of lattice points per cell includes contributions from interior points, face points, and corner points.
The number of lattice points per cell includes contributions from interior points, face points, and corner points.
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The structure of magnesium is face-centered cubic (FCC).
The structure of magnesium is face-centered cubic (FCC).
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Study Notes
Crystallography
- Crystallography is a branch of chemistry for second-year students.
- The majority of 92 stable elements are metallic.
- 68 of the stable metallic elements have one of three fundamental structures: body-centered cubic (BCC), face-centered cubic (FCC), or hexagonal close-packed (HCP).
Structures of Common Materials
- BCC Structure:
- Described by a non-primitive cubic unit cell.
- Contains one lattice point at each corner and one at the center of the unit cell.
- 21 metallic elements have this structure, mostly rare-earths.
- Characteristics:
- Ductile at high temperatures.
- Resistant to crack propagation.
- Brittle at low temperatures.
- Strength influenced by temperature.
- Hardened by interstitial solutes.
- FCC Structure:
- Described by a non-primitive cubic unit cell.
- Contains one lattice point at each corner and one at the center of each face.
- 17 metallic elements have this structure.
- Characteristics:
- Highly ductile when pure.
- Resistant to crack propagation.
- Retains ductility and toughness to absolute zero (unique among structures).
- HCP Structure:
- Described by layers of spheres, where spheres in alternating layers overlie one another.
- A close-packed structure with a slip system
- Common in elements like Beryllium, Cadmium, Magnesium, Titanium, Zinc, and Zirconium.
- Elastic nature.
Lattice Constant and Atomic Radius
- A table provides lattice constant (a and c, in nm) and atomic radius (in nm) for various metals categorized by structure (BCC, FCC, HCP).
Coordination Number
- Defined as the number of nearest neighbors of a central atom or ion within a solid.
- Examples show coordination numbers: 3, 4, 6, and 8, with corresponding shapes like triangles, tetrahedrons, octahedrons, and cubes.
- BCC coordination number is 8.
- FCC coordination number is 12.
- HCP coordination number is 12.
The number of lattice points per cell
- Atoms inside the cell are considered as 1 atom within the cell.
- Atoms on faces are sharing with 1/2 atom within the cell.
- Atoms on edges are sharing 1/4 atom within the cell.
- Atoms in corners are sharing with 1/8 atom within the cell.
Atomic Packing Factor
- Atomic packing factor (APF) is a ratio of the volume of atoms in a unit cell to the volume of the unit cell itself.
- APF reflects how closely atoms are packed.
- APF for different structures (BCC, FCC, Simple cubic, and HCP) is calculated based on the relevant formulae.
Structure-Property Correlation
- Ductility of aluminum is explained by its FCC crystal structure.
- Steel's (iron) properties are discussed compared to its BCC structure.
- Slip systems in metals are discussed as a way for plastic deformation to occur.
- Slip systems are closely related to the close-packed nature of the planes.
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Description
This quiz explores the principles of crystallography, focusing on the structures of common materials like BCC and FCC. It is designed for second-year chemistry students, covering the fundamental characteristics and behaviors of stable metallic elements. Test your understanding of how these structures affect material properties and applications.
