Core 2: Solid State Flashcards
How do you draw cell projections?
Show the 2D shape of the unit cell using the corner atoms and show the other positions where atoms are. Write a legend to show what atoms are in each position.
Where are the octahedral and tetrahedral holes in a fcc, how many for each are there? How do their sizes compare?
There are 4 octahedral holes, 12 on the edges and 1 in the centre.
There are 8 tetrahedral holes, 4 in the gap between the centre and outside facing plane for each side of the unit cell.
Tetrahedral holes are smaller than octahedral holes.
How can lattice enthalpies be predicted?
How can this be adjusted for covalent interactions?
The Coulomb interaction can be used with the Madelung constant, A, to account for the nearest neighbours.
A (1-p/r) constant is added where p is polarisability.
What does the Bragg equation describe and do?
The angle at which light is reflected by 2 parallel planes to which they stay in phase. The angle can be used to find the distance between planes and systematic absences are show based on the crystal structure.
What are the coordination numbers of the 3 cubic structures?
fcc - 12
bcc - 8
primative cubic - 6
How can the hardness of a metal be predicted by the type of close packing it has?
CCP structure has 8 slip planes whereas HCP only has 1 slip plane. More slip planes means the metal is softer.
What are the 2 types of close packed structures? What is the difference between their 3rd layer of atoms and what are their coordination numbers?
Hexagonal close packed and cubic close packed(fcc).
HCP packs the 3rd layer the same as the first, ABABAB
CCP packs the 3rd layer in the holes made by the first 2 ABCABC
Both have a coordination number of 12
How can crystal structure be predicited?
What does this method not consider?
Using the ratio of r+/r-
Tetrahedral 0.23-0.41
Octahedral 0.41-0.73
Covalent interactions not considered
What coordination numbers can exist for binary solids?
Tetrahedral - 4, Octahedral - 6, Cubic - 8
If all tetrahedral holes are filled then each lattice atom of the other type has a cubic coordination.
How many unit cell shapes are there and how many ways of arranging atoms in these shapes are there?
What are the 4 types of atoms occupying a unit cell?
7 lattice types, 14 ways of arranging atoms.
P - primative I - body-centered F - (all) face-centered C - (one) face-centered
What is the unit cell defined by?
Shape, size, symmetry and number of atoms
How are Miller indices derived?
How is -1 represented
The plane cuts a cell at values of a, the cell parameter so divide by a. Take the reciprocal of the new value.
1 bar
How can the lattice enthalpy be estimated without knowing the crystal structure?
The Madelung constant, A, divided by the number of atoms in the formula, v, gives very similar values, estimated as k. Therefore A can be substituted for kv.
What are the packing efficiencies of primative cubic and bcc structures?
Primative cubic - 52.4%
BCC - 68%
Why are bcc metals harder than close packed metals?
They aren’t as tightly packed together than the close packed strutures so it is harder for the layers to slip past each other.
