Face-centered cubic

Definition

Face-centered cubic (FCC) is a type of crystal structure where atoms are located at each of the corners and the centers of all the faces of the cube. This arrangement allows for a high packing efficiency and coordination number, which influences the physical properties of materials, particularly metals. The FCC structure is known for its strength and ductility, making it a common arrangement found in many metals like aluminum, copper, and gold.

5 Must Know Facts For Your Next Test

1. The face-centered cubic structure has a coordination number of 12, meaning each atom is surrounded by 12 other atoms.
2. The packing efficiency for FCC is about 74%, which is one of the highest among crystal structures.
3. In FCC crystals, the edge length can be calculated using the formula: `a = 2√2r`, where 'a' is the edge length and 'r' is the atomic radius.
4. FCC metals typically exhibit high ductility due to their ability to accommodate dislocations in their crystal lattice.
5. Examples of elements with an FCC structure include nickel, lead, and silver, which demonstrate various metallic properties influenced by this arrangement.

Review Questions

• How does the coordination number in face-centered cubic structures affect the physical properties of metals?
  • The coordination number of 12 in face-centered cubic structures indicates that each atom is surrounded by 12 neighboring atoms. This high coordination number contributes to stronger metallic bonding and enhances ductility, allowing metals with this structure to deform more easily under stress without breaking. As a result, metals like aluminum and copper exhibit excellent mechanical properties that are beneficial for various applications.
• Discuss how packing efficiency in face-centered cubic structures compares to other types of crystal lattices and its implications on material strength.
  • Packing efficiency in face-centered cubic structures is about 74%, which is higher than body-centered cubic structures (approximately 68%) and simple cubic structures (about 52%). This high packing efficiency means that more atoms occupy a given volume, leading to stronger metallic bonds and greater material strength. Consequently, metals with FCC structures often possess enhanced mechanical properties such as increased tensile strength and resistance to deformation.
• Evaluate the role of face-centered cubic structures in determining the mechanical behavior of metals used in engineering applications.
  • Face-centered cubic structures significantly influence the mechanical behavior of metals used in engineering due to their high coordination number and packing efficiency. These characteristics result in strong metallic bonding and allow for greater ductility, making FCC metals ideal for applications that require formability and toughness. For instance, when considering materials for construction or manufacturing processes, understanding how FCC arrangements contribute to performance under stress helps engineers select suitable materials that can withstand mechanical loads while maintaining structural integrity.

Related terms

Coordination Number: The number of nearest neighboring atoms surrounding a central atom in a crystal lattice.

Packing Efficiency: The fraction of volume in a crystal structure that is occupied by the atoms, usually expressed as a percentage.

Body-Centered Cubic: Another type of cubic crystal structure where atoms are located at each corner and one atom is positioned at the center of the cube.