OIA1011 CRYSTALLINE STRUCTURES, UNIT CELLS AND PACKING

What are the two main types of solids?

Crystalline (ordered structure) and amorphous (disordered structure) solids

Define a unit cell.

The simplest repeating unit of a crystal lattice that represents the entire structure when repeated in 3D

What is the coordination number in a crystal lattice?

The number of nearest neighboring atoms or ions surrounding a particle in a lattice

How do crystalline solids differ from amorphous solids?

Crystalline solids have a regular lattice and sharp melting points, while amorphous solids lack a defined structure and melt over a range of temperatures

Give an example of a crystalline solid and an amorphous solid.

Crystalline: Sodium chloride; Amorphous: Glass

Why do amorphous solids have higher solubility than crystalline solids?

The disordered structure of amorphous solids makes them more readily dissolve

Name the three main types of cubic unit cells.

Simple cubic (SC), body-centered cubic (BCC), and face-centered cubic (FCC)

What is the packing efficiency of simple cubic structures?

52.3%, with a coordination number of 6

What is the coordination number of BCC structures?

8, with a packing efficiency of 68%

What is the most efficient packing structure?

FCC or cubic closest packing (CCP), with a packing efficiency of 74% and a coordination number of 12

What are the two closest packing arrangements in crystals?

Hexagonal close-packed (HCP) and cubic closest packing (CCP)

How do HCP and CCP differ?

HCP follows an ABAB pattern, while CCP follows an ABCABC pattern

Why is CCP also known as FCC?

Because the unit cell arrangement of CCP corresponds to face-centered cubic packing

What are the four types of crystalline solids?

Ionic, metallic, covalent-network, and molecular solids

What are the key properties of ionic solids?

Hard, brittle, high melting points, and good electrical conductivity in molten form

Why are metallic solids good conductors of electricity?

They have delocalized electrons (a "sea of electrons") allowing free movement

Provide an example of a covalent-network solid.

Diamond, known for its hardness and high melting point

What is a common property of molecular solids?

They are soft, have low melting points, and are poor conductors of electricity

How does the packing efficiency affect material properties?

Higher packing efficiency results in greater density and stability

Why is understanding unit cell geometry important IN pharmaceutics?

It influences drug solubility, stability, and manufacturing

What is an example of a metal that crystallizes in the FCC structure?

Copper and silver

How is the packing efficiency of a primitive cell calculated?

By dividing the volume of spheres in the unit cell by the total volume of the unit cell

What are examples of HCP metals?

Magnesium and zinc

Which crystalline structure is most common for salts like NaCl?

Ionic crystalline structure

What determines crystal structure?

Atom size, intermolecular forces, and energy minimization

How do intermolecular forces influence molecular solids?

They determine melting points and hardness

How is the coordination number related to density?

Higher coordination numbers often indicate more densely packed structures

What is the coordination number for HCP structures?

12, the same as FCC

Why is crystalline structure critical in pharmaceuticals?

It impacts drug solubility, bioavailability, and manufacturing processes

How does polymorphism relate to unit cell structures?

Different polymorphs of a compound may have distinct unit cell arrangements, affecting their properties