2: Solid state Chem Flashcards
Topic 2 (37 cards)
Crystalline solids
atoms, ions or molecules of the material are arranged in a definite repeating pattern
The repeating patterns are fundamental properties and influence macroscopic behaviour
Metals, ions and small molecules typically for crystals
Amorphous solids
form when liquids freeze before the molecules can arrange into an orderly pattern
Lack ordered internal structure
Glasses
Non-crystalline materials
Large molecules or mixtures with restricted movement often form amorphous solids
Molecules that can form both amorphous and crystalline solids
Silicon dioxide can crystallise in several crystalline forms (quartz)
Rapid cooling forms amorphous fused silica
Types of crystalline solids
Ionic, metallic, covalent network, molecular
Ionic solids
made up of ions
positive and negatively charged ions
hard but brittle and shatter
high lattice energies
high m.p.
not conductive when solid
conductive when molten
Ionic solids
made up of ions
positive and negatively charged ions
hard but brittle and shatter
high lattice energies
high m.p.
not conductive when solid
conductive when molten
NaCl
Metallic solids
Atomic nuclei in a sea of delocalised electrons
metallic bonding
hard, malleable, don’t shatter
high thermal and electric conductivity
variable melting points
Copper
Covalent network solids
3D network of covalent bonds
non-metals
strong covalent bonds
very high m.p
Diamond
Molecular solids
neutral molecules held together by intermolecular forces
M.p varies based on intermolecular forces
small symmetrical non-polar molecules have weak attractive forces low m.p
molecules with permanent dipole higher m.p
H2O
Types of cubic unit cell
simple, face-centred, body-centred
Simple cubic unit cell
- Particles at 8 corners
- No central particle
- Spheres touch
- Not packed efficiently
- 48% empty
- Metallic polonium = only known example
- Each atom touching 6 others
- Coordination no. = 6
- PPUC = 8 x (1/8) = 1
Density of unit cell
Find number of particles in unit cell
PPUC
D = M/V
V = 2r^3
Find mass per particle
Molar mass/6 x 10^23 = mass per particle
D = M/V
Body-centred cubic unit cell
- Particles at all 8 corners
- 1 particle in the centre
- Centre particle touches all corners
- More efficiently packed than simple cubic
- 32% empty space
- Common structure for metals
- Lithium
- CN = 8. central atom touching 8 corner
- PPUC = (1)(1) + (8)(1/8) = 2
Face-centred cubic
- Particles at all 8 corners
- Particles at the centre of all 6 faces
- No central particle
- Corner spheres touch face spheres but not other corners
- Very efficiently packed
- 26% empty space
- Common for metals
- Al, Ca, Ni
- Copper
- CN = 12
- PPUC = (6)(1/2) + (8)(1/8) = 4
Copper as an antimicrobial surface
- copper shows contact killing effect
- copper surfaces kill pathogens
- likely due to release of ions leads to radical oxygen species that damage DNA and membrane
Hexagonal close packing
triangular holes
one layer offset from the other
74% packing efficiency
Magnesium
Cubic close packing
3 layer offset from each other
fcc
74% packing efficiency
Copper
Interstitial sites
- Smaller cations fit into holes
- Not all holes equal shape and size
- for every n particles there are n octahedral holes and 2n tetrahedral holes
Interstitial holes types
cubic hole
octahedral holes
tetrahedral holes
Cubic hole
a particle in this hole would touch 8 other particles
Octahedral hole
a particle in this hole would touch 6 other particles
Tetrahedral hole
a particle in this hole would touch 4 other particles
Cation and anion of similar size lattice
AB structure
- Caesium chloride (CsCl)
- Simple cubic lattice
- large anion fills cubic hole in centre
- NOT bcc AS ALL PARTICLES NOT IDENTICAL
- Anion:Cation = 1:1
- 1 CsCl/cell
Cations smaller than anions lattice AB structure
- NaCl
- FCC Na in octahedral holes
- 1:1
- alkali halides
- alkali hydrides
- monoxides
- monosulphides
