133B- solid chem Flashcards
what type of packing are these
what is a unit cell of ccp
what is a unit cell of ccp
What is the only element forming primitive cubic
palladium
What elements form body centred cubic
metals
equation for packing efficiency
How to work out the volume of atoms in a unit cell in ccp
How to work out the packing efficiency for ccp
out of
hexagonal close packing,
cubic close packing,
body centred cubic and
primitive cubic,
which structures are the best at packing
ccp
How does the energy of the 2s orbital in lithium change between Li, Li2, Li3, li4 etc.
molecular orbitals getting closer in energy when atom no increases resulting in a ‘band’
What must a material have to conduct electricity
partially filled conduction band
What type of alloy is this
substitutional- atoms of one metal are exchanged for those of another metal/ sizes of atoms must be similar
-happens randomly in sub alloys and diagram inst a repeating unit
What type of alloy is this
interstitial- new atom sits in interstitial position/ atoms of one element are present in the interstitial sites of a metal lattice
NaCl- what are positions of the chloride and sodium ions
-cubic close packing/ fcc of chlorine ions
-sodium are on edges and in middle so octrahedral interstitial sites [forms 6 bonds]
large anion usually gives lattice and smaller gives interstitial (cation)
FeS2 has the same structure as NaCl . Where would the Fe cations and S2 anions be
Fe 2+ would be where the sodium Ions are/ S2 are bonded together as a pair (-2 together) and sit where the chlorine would
What type of tetrahedral packing is this in ZnS
S only filling half the tetrahedral sites/ alternating
What type of packing does each element have and what site is half filled
For both structures anions are close packed and the cations occupy half of the octahedral sites.
CdCl2 has ABC packing
CdI2 has ABA packing
-octrahedral sites half filled by Cd in the CdCl2 still
G1 halides have sodium structure, what is the exception to this
caesium
Describe the sites of Ti (blue) and O2 (red)
[The structure is not cubic as one unit cell length is longer than the other two]
Ti is on the edges and in the middle,
Ti is octrahedral [as it forms 6 bonds] and O is trigonal planar [forms 3]
What do all calculations assume about the atoms/ions in a unit cell
and what is the assumptions of ions in a lattice structure
ions are charged, fixed-sized hard spheres
and
In an ionic solid, the ions are assumed to be in contact with their nearest neighbour of the opposite charge (used for equation r/r)
What are the trends in ionic radii across a period and across the whole table
-Ionic radii increase down a group (increasing principal quantum no)
-cations are generally smaller than anions
-cations get smaller with increasing charge and anions get bigger with increasing charge
What is the difference between an insulator and semi conductor conduction band
insulators- large gap so there in no electrons sitting in empty band so no conduction. electrons don’t have enough thermal energy to move there.
semiconductor- gap is smaller so heating could give e- enough energy
What dictates which alloy is made
size of new atom coming in
Which atomisation value would you use for this harber cycle ΔaH(Cl) or ΔaHo(Cl2)
ΔaHo(Cl)- this is bond dissociation for 1 mole of Cl gas to one mole Cl- ions wheras
ΔaHo(Cl2)- would need to be halved as it is 1 mole Cl2 gas to 2 moles Cl- ions
There are different definitions for ‘electron gain enthalpy’ (adding an electron to make an ion e.g adding electron to chlorine). Another name for it is electron affinity but what is different about that definition
electron affinity is same value but opposite sign
what is the packing of the anions and cations
cubic close packing of calcium cations with the fluoride anions in the tetrahedral interstitial sites
What do we assume about the equation below when doing lattice calculations
assume H and U are the same U= heat change constant volume H=U +pV
diff between lattice enthalpy and lattice energy is normally relatively small and can usually be ignored.
what does 1/n take account for
repulsive energy from electron clouds
what does n stand for (Born exponent)
compressibility of a compound/element and is dependant on its amount of electrons
Do you need to take into account positive and negative signs for z in the calculation
no- if if its MgO, z would be +2 for both of them so the calculation would be 2x2
What will the n of NaCl be
n=8; average between the n of both ions
How does the lattice energy change between structures that have low charge ions and ones that have high charge ones
higher charges will have higher lattice E, e.g MgO will have higher lattice E than NaCl
What does the Madelung constant depend on
the structure- e.g something with the same structure as NaCl will have the same Madelung constant
if calc lattice E is lower than expected lattice E the covalent character is high/low
high
if calc lattice E and expected lattice E are similar covalent character is high/low
low
How do the units of r and U differ from equations
Kapustinskii- r= pcm and will give answer in KJmol-1 Born-Landé - r=m and answer is in J
What is the difference between the Kapustinskii and Madelung equations
Kapustinskii is more of an approximation than Madelung
equation for radius ratio and what does it tell you
limiting radius ratio- the smallest possible value of the radius ratio for the cations and anions to be contact. If the radius ratio is any smaller, the action-anion contact is lost.
**question still to do What is the packing efficiency of the body-centred cubic structure
greater electronegativity greater degree ionic bond, what type of bonding when electrongetavities are low
alloy, with metallic bonding
Na and K have low electrongetavites and little difference between them
what is the cell projection diagram for this structure and what is this packing called
ccp/ close cubic packed
-must have the key beside
What does this key mean
the yellow spheres are the first and last layer (which must be the same as the top and bottom are repeating units)
the blue dots are the middle layer as they are in between 0-1 and are 0.5 so must be halfway between top and bottom
cell projection diagram of body-centred cubic/bcc structure
cell projection diagram of hexagonal close-packed/ hcp
density equation
mass per unit volume
To work out the density of a unit cell you need its mass and volume. How do you work out the mass and volume of the unit cell ccp
mass = moles x RAM,
multiply the Mr by the number of atoms (4), then divide by avagadros constant which will give you gmol-1
for ccp the volume is always L^3 = (8)3/2 x r^3
what is the free space in a unit cell called
interstitial sites
which site is octrahedral and which is tetrahedral
for any close packed structure what is true of the ratio between atoms, hexagonal sites and tetrahedral sites ccp (fcc)/ hcp
what structures are not close packing
bcc and primitive cubic
which atoms have at octrahedral sites around them in ccp
everything along the middle line
what positions do the tetrahedral sites lie at
in cubic closed packed the tetrahedral sites share faces/edges and the octrahedral sites share faces/edges
Both sites share edges
in hexagonal closed packed the tetrahedral sites share faces/edges and the octrahedral sites share faces/edges
both share faces
which element does the tetrahedral sites fill
F2
Describe the packing of CaF2
Ca- cubic close packing
F2- tetrahedral interstitial sites
(second picture is if you had 4 units repeating next to the one shown)
The related structure in which there is a ccp arrangement of anions with cations in the tetrahedral sites is called the antifluorite structure
how many tetrahedral sites are there per atom in a close packed structure [I don’t know what this means]
2
How is CaF2 the anti flouride structure of NaCl
In NaCl- the anions are in close packed and the cations in the interstitial sites
However in CaF2, the opposite is true/ cations are in the close packed arrangement
What are the arrangement of ions in NiAs
Ni= cation
As= anion
Ar- hexagonal close packing
Ni- cations in the octahedral interstitial sites
The NiAs structure is often adopted by compounds with high covalent character
What type of compound would adopt this structure
components with a high covalent character
What’s the general rule when trying to find out the packing of a structure
one element will have a close packing structure and one will be in the interstitial site
What are all the types of close packing structures and which are the two that are not
close packing ccp and hcp
bcc and primitive are not close packing
Show the empirical formula is CaTiO3
What is the sin rule
How would you work out the limiting radius ratio (r+/r-) for something with a sodium chloride structure and what does this ratio represent
0.414 is the smallest value of the radius ratio for the NaCl structure for which the cations and anions are in contact. If the radius ratio is smaller, the cation-anion contact is lost and the structure becomes less stable than one with a lower coordination number
What happens when the radius ratio becomes smaller than the limiting radius ratio
the cation-anion contact is lost and the structure becomes less stable than one with a lower coordination number
How would you work out the limiting radius ratio (r+/r-) for something with a tetrahedral structure
What are their limiting radius ratios
A from the NaCl structure= 1.7476
define lattice enthalpy
enthalpy change for the conversion of one mole of the ionic solid into the gaseous ions
Use the Kapustinskii equation to figure out the lattice energy of LiCl and AgCl
k =107900pmkJmol–1,
What is the van Arkel– Ketelaar triangle
predicts the type of bonding a compound has dependant on the electronegativity of its elements
x axis- χ̅ average electronegativity over the two elements
y axis- Δχ difference in electronegativity
Estimate where MgF2 and MgI2 would be on a van Arkel-Ketelaar triangle
