12 Questions
What is a characteristic property of crystalline materials?
Long-range atomic order
What type of bonding is described as temporary and fluctuating with time?
Van der Waals bonding
Which type of materials lack a crystalline structure?
Amorphous materials
Which term describes molecules that have a permanent dipole moment?
Polar molecules
What model illustrates atoms as spheres touching each other at their closest points?
Atomic Hard-Sphere Model
On a bonding tetrahedron, what is located at each vertex to represent the four bonding types?
Van der Waals bond
Which crystal structure has atoms located at each of the cube's corners and center of its faces?
Face-Centered Cubic (FCC)
What term is used for atomic bonds that are mixtures of two or more extreme types of bonds?
Mixed bonds
What is the term used to represent small repeat entities in crystal structures?
Unit cells
What is the coordination number for face-centered cubic crystal structures?
8
Which material class is associated with metallic bonding?
Metals
What type of bonding is found in molecular solids?
Van der Waals bonding
Study Notes
Crystal Structure and Properties
- Crystal structure affects material properties, such as brittleness (e.g., magnesium and beryllium) vs. ductility (e.g., gold and silver)
- Noncrystalline materials (e.g., ceramics and polymers) are often optically transparent, whereas crystalline forms are opaque or translucent
Crystalline and Non-Crystalline Materials
- Crystalline materials have long-range atomic order, with atoms arranged in a repetitive three-dimensional pattern
- Non-crystalline materials lack long-range atomic order and exhibit no crystalline structure
Polycrystalline Materials
- Exhibit long-range order due to the formation of multiple small crystalline regions or grains, each with its own crystallographic orientation
Atomic Hard-Sphere Model
- Represents atoms as spheres that touch each other at their closest points, illustrating nearest-neighbor interactions
Lattice and Unit Cells
- Lattice refers to a three-dimensional array of points coinciding with atom positions (or sphere centers)
- Unit cells are small repeat entities that make up the crystal structure, often subdivided for convenience
Face-Centered Cubic (FCC) Crystal Structure
- Common crystal structure found in many metals, characterized by a cubic unit cell with atoms at corners and face centers
- Important characteristics include coordination number and atomic packing factor (APF)
Bonding Types
- Ionic, covalent, metallic, and van der Waals bonding types exist, and many real materials exhibit mixed bonding
- Bonding tetrahedron represents these bonding types, with mixed-bond types on the edges
- Correlations exist between bonding type and material class (e.g., polymers: covalent, metals: metallic, ceramics: ionic/mixed ionic-covalent)
Test your knowledge on Van der Waals forces, which are weak intermolecular forces between molecules or atoms caused by temporary or permanent dipoles. Learn about the attraction between molecules due to induced and permanent dipole moments.
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