Hexagonal

Definition

Hexagonal refers to a crystal system characterized by a six-fold symmetry, where the unit cell is defined by two equal axes in the horizontal plane and one vertical axis perpendicular to these. This unique arrangement allows for specific angles between the axes, most notably the angle of 120 degrees in the horizontal plane, and plays a critical role in the arrangement and properties of materials that crystallize in this system.

5 Must Know Facts For Your Next Test

1. The hexagonal crystal system includes two distinct Bravais lattices: the simple hexagonal and the hexagonal close-packed (HCP) lattices.
2. Materials such as graphite and zinc oxide exhibit hexagonal symmetry, which influences their physical properties, including conductivity and reactivity.
3. In a hexagonal unit cell, the angles between the axes are 90 degrees for the vertical axis with respect to the horizontal, while the horizontal axes form angles of 120 degrees with each other.
4. Hexagonal structures can lead to unique packing arrangements, allowing for high densities and close packing of atoms compared to other crystal systems.
5. The hexagonal system is commonly found in metals and minerals, affecting their mechanical strength and thermal properties due to the arrangement of atoms.

Review Questions

• How does the symmetry of a hexagonal crystal system impact its physical properties?
  • The symmetry inherent in a hexagonal crystal system directly influences its physical properties by dictating how atoms are arranged within the structure. For instance, materials like graphite benefit from this arrangement through enhanced electrical conductivity due to the free movement of electrons along their planes. Additionally, the unique angles and distances between atoms can affect how a material responds to stress, making some hexagonal crystals more durable than those from other systems.
• Compare and contrast the simple hexagonal and hexagonal close-packed (HCP) lattices regarding atomic arrangements and packing efficiency.
  • The simple hexagonal lattice features a less efficient packing arrangement compared to the hexagonal close-packed (HCP) lattice. In HCP, each atom is surrounded by 12 others, allowing for tighter packing and higher density. Conversely, while simple hexagonal has atoms positioned at each corner of the base with one atom at the center, it lacks the compact structure that HCP provides. This difference in atomic arrangements leads to variations in mechanical properties and stability.
• Evaluate how understanding the hexagonal crystal system contributes to advancements in material science and engineering.
  • Understanding the hexagonal crystal system is crucial for advancements in material science because it helps researchers predict and manipulate material properties based on their atomic structures. For instance, knowing that certain materials like graphene have hexagonal arrangements allows scientists to exploit their unique electrical and thermal conductivity characteristics for applications in electronics and energy storage. Additionally, insights into how hexagonal symmetry influences mechanical strength can guide engineers in developing stronger, lighter materials for aerospace and automotive industries, leading to innovation in design and functionality.

Related terms

Unit Cell: The smallest repeating unit in a crystal lattice that reflects the symmetry and arrangement of atoms in the crystal.

Bravais Lattices: A classification of lattice types based on their symmetry and geometry, of which hexagonal is one of the 14 distinct types.

Symmetry: The property of a crystal structure that describes how the arrangement of atoms or molecules is repetitive and orderly, including aspects like rotation and reflection.