Crystalline Structures Flashcards
How are atoms organised in crystalline solids?
In a crystalline solid, atoms are organised and bonded in repeated patterns - in a lattice structure.
Give examples of crystalline solids (5)
Diamond
Metals
Salt, sugar, snow
How are atoms organised in amorphous solids?
in an amorphous solid, there is no pattern to the arrangement of atoms
Give examples of amorphous solids (3)
Glass
Most plastics
Rubbers
What does BCC stand for?
Body centred cubic
What does FCC stand for?
Face centred cubic
Give 3 examples of BCC crystal structures.
iron (ferrite), Chromium, vanadium
Give 6 examples of FCC crystal structures.
Aluminium, copper, lead, silver, gold,
iron (austenite) - high temperatures only
Describe the structure of BCC metal crystal structure.
Atoms are positioned at the 8 corners of a cube, plus one atom in the middle of the cube
Describe the structure of FCC metal crystal structure.
Atoms are positioned at the 8 corners of a cube plus one atom in the middle of each face of the cube
Which metal crystal structure is more brittle? BCC or FCC?
BCC is more brittle
Which metal crystal structure is more ductile? BCC or FCC?
FCC is more ductile
Why are BCC metals more brittle? (3)
- The atoms are not closely packed, and they are not very ‘in-line’ with each other.
- A larger force is required to cause the atoms to slip over each other - there is more of a ‘hill’ to climb.
- Because the BCC structure blocks slip, BCC metals are stronger, less ductile and more brittle.
Why are FCC metals more ductile? (3)
- The atoms are more closely packed, and they are more ‘in-line’ with each other.
- A smaller force is required to cause the atoms to slip over each other - there is less of a ‘hill’ to climb.
- Because the FCC structure allows easier slip, FCC metals are more ductile and malleable, and less strong.
