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102 Cards in this Set
- Front
- Back
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List properties of a metal (4)
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Shiny
Conductive Malleable Ductile |
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How to crystal structures change? (3)
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With
Temperature Pressure Other physical processes |
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Define "Interstitial Solid Solution"
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randomly distributed atoms inserted into tetrahedral/octahedral holes
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Stress formula
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sigma = F/A
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Strain formula
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epsilon = delta l/l
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Young's Modulus formula
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E = sigma/epsilon
E = stress/strain |
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Define "Plasticity"
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changing shape irreversibly
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Name 3 ways plasticity can occur
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Slip - planes slide past each other
Twinning - deformation leads to twinning Shear Transformation - deformation leads to a new structure |
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What 3 things are used to compare the suitability of metals?
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Cost
Density Stiffness |
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Define "Perfect Metal"
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a stack of identical cubes, all angles 90 degrees
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Why are metals malleable?
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Bonding is non-directional
Dislocations propagate at the speed of sound shifting the whole crystal |
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In which planes does slip occur?
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The closest packed plane:
Cubic (111) BCC (110) HCP - plane of the hexagon |
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Give 3 examples of charge carriers
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Electrons
Holes Ions |
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What does the Fermi level describe?
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the highest energy electron (HOMO)
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Why are metals less hard than expected?
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Weak cohesive forces
Dislocations and errors |
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Why are alloys often harder than their parts?
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Cohesive energy increases
Different size atoms cause dislocations to be difficult Grain boundaries |
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What are band gaps?
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Forbidden energies of electrons
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Metal + nHX -->
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MXn + n/2 H2
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What does enthalpy of hydration depend on?
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Size
Charge |
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Define "Ligand"
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an atom, ion, or molecule that binds to a metal centre by a mixture of covalent and electrostatic effects forming a complex which may be neutral or charged.
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Types of ligands
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X - atom lacking 1/2 electrons
L - lone pair Z - neutral, Lewis acid, vacant orbital |
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Types of ligand binding
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Terminal (end on)
Bridge (notated using mew) Ambidentate (binds from DIFFERENT points) Multidentate (binds from MULTIPLE points) |
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How do you make a complex chiral?
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Use chiral ligands
Bind achiral ligands in a helical arrangement |
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Why multidentate ligands are preferred (chelate effect)
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Kinetics - second bond binds very quickly
Thermodynamics - more energy is released with 2 ligands Entropy increases |
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Why is enthalpy of hydration larger than expected for most first row transition metals?
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d electrons stabilise the metal cation
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Why are some transition metal complexes brightly coloured?
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Electrons move from ligand to metal = charge transfer
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What does d-orbital splitting depend on?
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Nature of ligand
Element Charge |
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Induced magnetic field formula
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m = xH
induced magnetic field = susceptibility x applied magnetic field |
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Diamagnetism
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induced magnetisation is opposite to applied field and independent of temperature, x < 0
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Paramagnetism
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induced magnetisation is in the same direction as the applied field, x > 0
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Curie's Law
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x is proportional to 1/T
hard to alighn electrons at high temperatures due to thermal motion |
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Magnetic moment formula
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sqrt n(n+2)
where n = number of unpaired electrons |
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Circumstances when electrons can jump to other orbitals (causing orbital angular momentum)
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Degenerate orbitals
Orbitals without electron of same spin (Pauli exclusion principle) Orbitals must be similar shape |
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Fermi Level Probabilities at zero Kelvin
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When E > Ef, P(E) = 0
When E < Ef, P(E) = 1 When E = Ef, P(E) = 1/2 |
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Define "Crystal Field Stabilisation Energy"
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the stability that results from placing a transition metal ion in a crystal field generated by a set of ligands. d-orbitals are split and some become lower and some higher in energy due to the interactions with the ligands.
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Why are axial bonds longer?
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There is more electron density in the plane of the molecule
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Where are stereochemically inert electron pairs found?
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In heavier members of the periodic table
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Ignoring Nitrogen, describe 7 properties as we descend Group 15
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Ionisation Energy lowers
Electronegativity lowers Radius increases Basicity increases Bond strength with halogens weakens due to reduced overlap Likelihood of +5 oxidation state decreases Overlap decreases - catenation increases |
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How does PR3 stabilist low oxidation state transition metals?
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By accepting electrons into the p(pi) orbital
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Ways to isolate Phosphorus
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Distil horse urine
Bone + carbon Reduce from crude calcium phosphate with carbon in a furnace |
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Properties of white phosphorus
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P4
White/Yellow Discrete Van der Waals molecule Soluble Volatile Pyrophoric When heated to 900 degrees celsius, becomes a gas and is in equilibrium with P2 |
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Properties of red phosphorus
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(P4)n
red Infinite polymer Insoluble Not volatile |
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Define "Catenation"
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linking atoms of the same element into longer chains
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How do you isolate Arsenic?
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FeAsS --> FeS + As
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How do you isolate Antimony?
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Sb2S3 + 3Fe --> 3FeS + 2Sb
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What does soft mean?
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polarisable electron density
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Why can phosphines be chiral, unlike amines?
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Slow inversion of tetrahedral phosphine due to difference in energy of s and p-orbitals, so rehybridisation is slow
For amines - too fast |
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Why are phopshites less basic than phosphines?
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O in phosphite draws electron density away from the lone pair on P
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Define "Phosphonium Ylid"
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a zwitter-ion with opposite charges on neighbouring atoms
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How do you add a fifth alkyl group to phosphorus?
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[Ph4P]+I- + PhLi --> Ph5P + LiI
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How do you create P-P bonds?
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2R2PCl + 2Na + (NH3) --> R2P-PR2 + 2NaCl
small R groups make 5 membered rings with envelope conformation |
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What are phosphazines?
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Unsaturated phosphazenes
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What is an oligamer?
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Small polymer with n = 2 --> 15
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How do you create a phospazene?
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PCl5 + NH4Cl --> (PNCl2)n + 4HCL
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What reactants are required to make large P/S cage structures?
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P4 + S8
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pKa
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-logKa
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What does acid strength depend on?
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Stability of the anion
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What affects stability of the anion?
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The ability to "handle" negative charge which is aided by delocalisation (canonical forms)
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Bells Rule
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HnEOm
the larger the difference (m-n), the stronger the acid |
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List 8 applications of phosphates
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Paint stripper
Manufacture of processed cheese Laxatives Fertiliser Flame retardant Baking powder Toothpaste Water Softener (binds to Ca/Mg ions) |
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What is a zeolite?
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microporous crystalline solid containing aluminium and silicon which safely removes heavy metals and toxins
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Why is I3n-NH3 explosive?
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NI3 --> I2 + N2
I2 is shock sensitive and the reaction is driven by formation of N-N triple bond. Activation energy is overcome by tapping the powder with a stick. |
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What state are PX5 compounds found in?
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PF5 - gas
PCl5 - solid PBr5 - solid PI5 - unknown |
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List 3 properties of tertiary phoshines
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Unpleasant smell
Easily oxidised in air to phosphine oxide Liquids (except very large R groups) |
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Define the "Tolman Cone Angle"
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the angle at the metal swept out by the van der Waals radius of the groups attached to the phosphorus atom
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Define "Crystal"
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atoms are arranged periodically
a sub-unit can be used to tessellate the full structure there is short and long range order |
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Define "Amorphous"
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short but no long range order
no unique sub-unit can generate the full structure caused by rapid cooling locking atoms in non-equilibrium positions |
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Define "Annealing"
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slowly heating and cooling repetitively to form a perfectly ordered state
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Define "Lattice"
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an infinite array of points where each point has identical surroundings
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Define "Unit Cell"
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a motif which when repeated in directions gives the lattice
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Define "Miller Indice"
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denotes planes of atoms in a crystal
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Properties of Triclinic Bravais Lattice
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a / b / c
alpha / beta / gamma / 90 degrees |
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Properties of Monoclinic Bravais Lattice
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a / b / c
alpha = gamma = 90 degrees / beta > 90 degrees |
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Properties of Orthorhombic Bravais Lattice
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a / b / c
alpha = beta = gamma = 90 degrees (cuboid) |
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Properties of Hexagonal Bravais Lattice
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a = b / c
alpha = beta = 90 degrees, gamma = 120 degrees |
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Properties of Rhomahedral Bravais Lattice
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a = b = c
alpha = beta = gamma / 90 degrees |
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Properties of Tetragonal Bravais Lattice
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a = b / c
alpha = beta = gamma = 90 degrees |
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Properties of Cubic Bravais Lattice
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a = b= c
alpha = beta = gamma = 90 degrees |
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Steps to determine crystal structure
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High energy electrons are fired at the sample
Core electrons are excited Excited electrons drop back emitting X-ray radiation Angle of diffraction is found by comparison with a transmitted beam |
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Bragg's law
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n lambda = 2dsin theta
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How do covalent bonds affect packing?
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covalent bonds are longer, so less packing
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As bond polarity increases...
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structures lower in dimension
3D --> 2D --> 1D |
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Radius ratios
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0.225 - coordination 4
0.414 - coordination 6 - primitive 0.732 - coordination 8 - BCC |
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Density =
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mass/volume
M (mass of formula unit) x Z (no. of units) / V x Na |
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Define "Lattice Energy"
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the energy change when one mole of gaseous ions, which are infinitely separated, form a crystal at zero Kelvin
always exothermic |
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Coulomb attraction formula
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delta U = ZaZbe^2 / 4 x pi x epsilon x r
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Madelung formula
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delta U = NaZaZbe^2 / 4 x pi x epsilon x r
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delta U (repulsion)
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= B (repulsive constant) / r^n (n = Born exponent)
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To find lattice enthalpy using Hess cycle
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Constituent elements are atomised to gaseous atoms which are ionised/affinity to gaseous ions then lattice enthalpy
all equal to enthalpy of formation |
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Failings of Born-Lande Equation
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highly polarisable ions affect the true value
improved by taking van der Waala into account |
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Tetrahedral holes
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4 neighbours
0.225r positioned a quarter in every dimension from each vertice |
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Octahedral holes
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6 neighbours
0.414r half way along every edge |
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NaCl
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Cubic close packed with Na in octahedral holes
coordination 6:6 |
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CaF2
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Cubic close packed with Ca in tetrahedal holes
coordination 8:4 |
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CsCl
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two interpenetrating primitive cubic cells
coordination 8:8 |
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NiAs
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Hexagonal close packed with Ni in octahedral holes
coordination 6:6 |
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CdI2
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Hexagonal close packed with Cd in octahedral holes of alternating layers
coordination 3:6 |
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TiO2
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distorted hexagonal close packed with Ti in half the octahedral holes
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ZnS blende
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cubic close packed with Zn in half the tetrahedral holes
coordination 4:4 |
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ZnS wurtzite
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hexagonal close packed with Zn in alternate tetrahedral holes
coordination 4:4 |
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Failings of using metal hydrides to store hydrogen?
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H is apolar
low electron density binds weakly within structures (via van der Waals) - called physisorption |
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As move across period, metal hydrides...
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decrease in density
melting point lowers covalent character increases |
