1- Nature Of Solid Material

Question 1

Crystalline

Answer 1

majority of natural materials- ordered in regular pattern in 3D
e.g
Halite (NaCla)
Fluorite (CaF2)

Question 2

Amorphous

Answer 2

totally disordered

Question 3

Glass

Answer 3

(Super cooled liquid) some order inherited from the liquid state but not enough time to order into a crystal
- atoms roughly the same distance apart, some areas with regular order

Question 4

Why do crystalline Solids form?

Answer 4

• Bond distances optimised
• Bond angles optimised
• Every atom in an optimum site
• Everything in its place

ALL ENERGIES MINIMISED

Question 5

Why do non-Crystalline Solids form?

Answer 5

Often have SHORT-RANGE ORDER(local areas where coordination is not random)

ENTROPY requires some disorder in high temperature mater

• If you freeze melts or solutions too fast, they may not have time to crystalise and from non-crystalline solids
• Sometimes crystalline solids can lose order if they contain radioactive elements
• Radiation machine-guns the structure smashing it up and making it amorphous (usually contain U)

Question 6

The change into a crystalline solid is called:

Answer 6

DEVITRIFICATION

Snowflakes in obsidian are where the glass has partly devitrified

Question 7

MINERAL Vs ROCK Vs Glass

Answer 7

A Mineral is a naturally occurring solid material, usually crystalline (but possibly amorphous) with a chemical composition which is essentially constant (within definable limits)

A Rock is a naturally occurring aggregate of mineral grains which may include several different minerals.

Glasses are considered as ROCKS since their compositions are very variable.