Atomic Arrangements in Solids Flashcards
What are the types of solids?
Crystalline material, single crystal, polycrystalline, amorphous
What is a crystalline material?
Atoms self-organise in a periodic array
What is a single crystal?
Atoms are in a repeating or periodic array over the entire extent of the material
What is a polycrystalline material?
Comprising of many small crystals or grains
What is an amorphous solid?
disordered - lack of systematic atomic arrangement
What are the atomic properties of a crystalline solid?
The bonds between each atom/ion/molecule are equal. The melting point is extremely precise. Most stable of solids.
What are the atomic properties of amorphous solids?
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.
Why do atoms assemble into ordered structures?
The atoms tend to a minimum energy which is a repetitive spatial ordering.
Which solids have crystalline state?
Metals, alloys, ceramics, some polymers.
What is a unit cell?
A structural unit that can describe a crystal structure.
What are the main metallic structures?
Body-Centred Cubic (BCC). Face-centred cubic (FCC). Hexagonal Close-Packed (HCP).
What sets the density of a material?
Percent packing efficiency. The higher the packing efficiency the more favourable the properties.
What is the highest packing efficiency of atoms of all of one size?
74%
Describe face-centred cubic structure
Atoms are located at each of the corners and centres of all the faces of the cubic unit cell. 74% packing efficient
Which metals use FCC?
Copper, aluminium, silver, gold
How do you work out the packing efficiency?
Volume of atoms in a unit cell / total unit cell volume
Describe body-centred cubic structure (BCC)
Atoms are located at the corners and centre of the cubic unit cell. 68% efficient.
Describe hexagonal closed-packed structure
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%
Which metals use HCP?
cadmium, magnesium, zinc, titanium
How do you work out the density of a material?
= N-atoms * Mass-per-atom / volume of unit cell
What are grain boundaries?
The mismatch regions between the grains of a polycrystalline material.
How many atoms can be found in a
(a) body-centred cubic structure
(b) a face-centred cubic structure
(c) Hexagonal closed-packed structure
(a) 2
(b) 4
(c) 6
