Hexagonal close-packed

Definition

Hexagonal close-packed (hcp) is a type of crystal structure where atoms are arranged in a hexagonal lattice, creating a densely packed formation. This arrangement is characterized by layers of atoms stacked in a specific sequence that maximizes space efficiency, providing high packing density. The hcp structure is notable for its strong interatomic interactions and plays a crucial role in determining the physical properties of materials such as metals and alloys.

5 Must Know Facts For Your Next Test

1. In hexagonal close-packed structures, each atom has a coordination number of 12, meaning it is surrounded by 12 neighboring atoms.
2. The hcp structure consists of alternating layers of atoms in the ABAB pattern, where A and B denote different layers.
3. Common elements that adopt the hexagonal close-packed structure include magnesium, titanium, and zinc.
4. Hexagonal close-packed materials often exhibit unique mechanical properties, such as increased strength and ductility compared to other crystal structures.
5. The hcp configuration is one of the two most efficient ways to pack spheres in three-dimensional space, with the other being cubic close-packed.

Review Questions

• How does the arrangement of atoms in the hexagonal close-packed structure influence its physical properties?
  • The arrangement of atoms in a hexagonal close-packed structure leads to a high packing density, which enhances the strength and stability of the material. With a coordination number of 12, atoms in this configuration have strong interatomic interactions, resulting in improved mechanical properties like ductility and hardness. This dense arrangement allows hcp materials to withstand greater stress and deformation compared to less efficiently packed structures.
• Compare the hexagonal close-packed and cubic close-packed structures in terms of atomic arrangement and coordination number.
  • Hexagonal close-packed structures feature an ABAB layering sequence with a coordination number of 12, indicating that each atom is surrounded by 12 others. In contrast, cubic close-packed structures have an ABCABC layering sequence but also possess a coordination number of 12. While both structures achieve high packing efficiency, their different layering sequences can influence other properties such as slip systems during deformation.
• Evaluate the significance of the hexagonal close-packed structure in materials science and its applications in technology.
  • The hexagonal close-packed structure is significant in materials science because it helps determine the mechanical and thermal properties of metals and alloys used in various technologies. Its unique atomic arrangement leads to superior strength and ductility, making hcp materials ideal for applications such as aerospace components and automotive parts. Understanding hcp structures allows engineers to tailor materials for specific performance requirements, influencing advancements in manufacturing processes and product development.

Related terms

Cubic close-packed: A crystal structure where atoms are arranged in a cubic lattice, also known for its high packing efficiency and typically found in metals like copper and aluminum.

Lattice: A systematic arrangement of points in space that represents the positions of atoms in a crystalline solid, forming the basis for understanding crystal structures.

Coordination number: The number of nearest neighbor atoms surrounding a central atom in a crystal structure, which helps describe the arrangement and bonding of atoms.