Ionic Crystal Structures and Geometry

The video tutorial explains the complexity of ceramic crystal structures compared to metals, focusing on the roles of charge neutrality and size differences between anions and cations. It discusses how these factors lead to various coordination numbers and stable structures. The tutorial also covers how the ratio of cation to anion size determines the geometry of the crystal structure, such as linear, trigonal planar, tetrahedral, and octahedral arrangements.

Why are ceramic crystal structures more complex than those of metals?

• Ceramics have more uniform ion sizes.

• Ceramics involve both positive and negative charges and varying ion sizes.

• Ceramics are made of only one type of atom.

• Ceramics have fewer types of ions.

In a charge-neutral crystal structure, what determines the number of neighboring ions?

• The age of the crystal.

• The chemical formula of the compound.

• The temperature of the environment.

• The color of the ions.

What is the typical size relationship between cations and anions?

• Cations are larger than anions.

• Cations are always spherical.

• Cations and anions are the same size.

• Cations are smaller than anions.

What happens if a cation is too small to touch the surrounding anions?

• The structure becomes more stable.

• The structure becomes unstable.

• The anions shrink to fit.

• The cation grows larger.

What type of geometry is formed when the cation to anion size ratio is less than 0.155?

• Linear

• Octahedral

• Trigonal planar

• Tetrahedral

Which geometric arrangement is associated with a cation to anion size ratio between 0.155 and 0.225?

• Linear

• Trigonal planar

• Tetrahedral

• Cubic

What is the coordination number for a tetrahedral geometry?

• 8

• 3

• 4

• 6

What coordination number is associated with octahedral geometry?

• 8

• 12

• 4

• 6

In which structure is an atom surrounded by 12 nearest neighbors?

• Hexagonal close-packed

• Simple cubic

• Face-centered cubic

• Body-centered cubic

What is the coordination number for a cubic geometry?

• 4

• 6

• 12

• 8