Crystals and Crystallisation (1/2) [Shankland] Flashcards Preview

PM2B Spring Amy L > Crystals and Crystallisation (1/2) [Shankland] > Flashcards

Flashcards in Crystals and Crystallisation (1/2) [Shankland] Deck (12):

Explain the arrangement of crystalline materials

Molecules are arranged in a regular manner
In 3 dimension
Over long ranges


How can it be found out whether a material is crystalline or amorphous?

Expose samples of the material to X-ray radiation
Scattered radiation = crystalline
Single broad peak = amorphous


List the 4 forces which hold a solid together

Non-covalent, intermolecular forces:
Electrostatic interaction = strong, occurs between ions
Hydrogen bond = intermediate, between 2 permanent dipoles
Dipole-dipole interaction = weak, arising from permanent dipoles
Dispersion = occurs between all molecules, arising from transient dipoles


Name the 4 types of crystal arrangement

Ionic = electrostatic interactions
Metallic = close-packed atoms
Covalent = covalent bonding
Molecular = van der Waals, hydrogen bonding and electrostatic interactions


Describe the arrangement of an ionic crystal

Held together by electrostatic interactions (e.g. Na+ & Cl-)
Regular, repeating pattern = long 3D order = crystalline


Describe the arrangement of a metallic crystal

Atoms are closely packed together
Atoms share electrons which are mobile, giving rise to conductivity


Describe the arrangement of a covalent crystal

Held together by covalent bonds
e.g diamond


Describe the arrangement of a molecular crystal

Held together by van der Waals, hydrogen bonding and electrostatic interactions
e.g. salt forms


How is a crystal described?

Molecular crystals consist of regularly arranged molecules in 3D extending (effectively) to infinity
"unit cell"


Which 3 bits of information about the unit cell is required in order to describe a crystal?

Size of the unit cell
Shape of the unit cell
Positions of atoms in the unit cell
(x, y, z dimensions)


Define: Polymorphs

Polymorphs are different 3D packing arrangements of the same object


How can polymorphs differ?

The size and shape of their unit cells
The location of the molecule inside their unit cells