SS - types and properties of inorganic crystalline materials

Question 1

Describe the crystalline state

Answer 1

In a crystal, atoms are arranged periodically. A sub-unit can be used to tesselate the full structure. There is short and long range order - transitional order

Question 2

Describe the amorphous structure

Answer 2

There is short range order but no long range order. There is no unique sub-unit that can be used to generate the full structure. There is no transitional order.

Question 3

State the 5 families of crystalline solids

Answer 3

• metallic
• ionic
• covalent
• molecular
• molecular ionic materials

Question 4

Describe metallic solids

Answer 4

Bonds are reasonably strong, hence the high melting points of metals. Atoms are surrounded by a sea of electrons.

Question 5

Describe covalent solids

Answer 5

All bonding in the solid is covalent, eg diamond and graphite. There is a build up of electron density between atoms.

Question 6

Describe ionic solids

Answer 6

The solid contains ions rather than uncharged atoms. The predominant interaction between ions is electrostatic. Eg salts such as NaCl

Question 7

Describe molecular solids

Answer 7

Discrete, uncharged and covalently bonded molecules are held together by London forces and sometimes hydrogen bonds. The bonding is typically quite weak, hence meting temperatures are quite low, eg ice.

Question 8

Describe molecular ionic solids

Answer 8

Molecules in these solids bare a charge so the electrostatic forces dominate. Materials are reasonably thermally stable. Eg CaCO₃

Question 9

Describe short-range order

Answer 9

Short-range order is present in both crystalline and amorphous solids. The term means there is local ordering, ie there is identical first (or second) neighbour coordination of atoms

Question 10

Describe long-range order

Answer 10

If a solid has long-range order, it is a crystalline solid. Each atom has identical surroundings.