Atomic Arrangements in Solids

Question 1

What are the types of solids?

Answer 1

Crystalline material, single crystal, polycrystalline, amorphous

Question 2

What is a crystalline material?

Answer 2

Atoms self-organise in a periodic array

Question 3

What is a single crystal?

Answer 3

Atoms are in a repeating or periodic array over the entire extent of the material

Question 4

What is a polycrystalline material?

Answer 4

Comprising of many small crystals or grains

Question 5

What is an amorphous solid?

Answer 5

disordered - lack of systematic atomic arrangement

Question 6

What are the atomic properties of a crystalline solid?

Answer 6

The bonds between each atom/ion/molecule are equal. The melting point is extremely precise. Most stable of solids.

Question 7

What are the atomic properties of amorphous solids?

Answer 7

The bonds between atoms/ions/molecules are all different. There is no regularity in the external surface. The melting point is more of a melting range. There structure is indistinguishable from a liquid.

Question 8

Why do atoms assemble into ordered structures?

Answer 8

The atoms tend to a minimum energy which is a repetitive spatial ordering.

Question 9

Which solids have crystalline state?

Answer 9

Metals, alloys, ceramics, some polymers.

Question 10

What is a unit cell?

Answer 10

A structural unit that can describe a crystal structure.

Question 11

What are the main metallic structures?

Answer 11

Body-Centred Cubic (BCC). Face-centred cubic (FCC). Hexagonal Close-Packed (HCP).

Question 12

What sets the density of a material?

Answer 12

Percent packing efficiency. The higher the packing efficiency the more favourable the properties.

Question 13

What is the highest packing efficiency of atoms of all of one size?

Answer 13

74%

Question 14

Describe face-centred cubic structure

Answer 14

Atoms are located at each of the corners and centres of all the faces of the cubic unit cell. 74% packing efficient

Question 15

Which metals use FCC?

Answer 15

Copper, aluminium, silver, gold

Question 16

How do you work out the packing efficiency?

Answer 16

Volume of atoms in a unit cell / total unit cell volume

Question 17

Describe body-centred cubic structure (BCC)

Answer 17

Atoms are located at the corners and centre of the cubic unit cell. 68% efficient.

Question 18

Describe hexagonal closed-packed structure

Answer 18

Six atoms form a hexagon around out central atom in a plane. Another plane is situated halfway up the unit cell with an additional 3 atoms. Then another hexagon plane. 74%

Question 19

Which metals use HCP?

Answer 19

cadmium, magnesium, zinc, titanium

Question 20

How do you work out the density of a material?

Answer 20

= N-atoms * Mass-per-atom / volume of unit cell

Question 21

What are grain boundaries?

Answer 21

The mismatch regions between the grains of a polycrystalline material.

Question 22

How many atoms can be found in a

(a) body-centred cubic structure
(b) a face-centred cubic structure
(c) Hexagonal closed-packed structure

Answer 22

(a) 2
(b) 4
(c) 6