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CHEM2017 - Physical Chem > Solid State Chemistry > Flashcards

Solid State Chemistry Flashcards

(91 cards)

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1
Q

What is a polycrystalline solid

A

lots of small crystals called grains packed together to form the solid, almost all metals made up like this

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2
Q

what amorphous solid

A

they have no long range order, theyre most plastics/living things

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3
Q

what are the 4 types of bonding in solids

A

covalent bonding, metallic bonding, ionic bonding and Van der waals

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4
Q

give some properties of covalent bonding

A

rigid, not conductive, high melting points. elements have similar electronegativities,

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5
Q

Give examples of VDWs bonding and explain properties

A

Intermolecular bonds between molecules holding crystals and solids together, Hydrogen bonds are the strongest, also include dipolar interactions. Theyre soft, non-conductive, low melting points

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6
Q

Why are ionic solids brittle?

A

arranged as alternating cations/anions which are attracted to each other but if displaced so cations next to cations this is highly repulsive

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7
Q

What is lattice enthalpy

A

change in internal energy when 1 mole of crsytal breaks into constituent ions

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8
Q

How do you find columbic energy (J)

A

Z+ x Z- x e2 / 4 x Pi x e0 x r

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9
Q

What is first ionisation energy

A

change in internal energy when 1 mole of gaseous atoms becomes one mole of gaseous monopositive ions

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10
Q

What is electron affinity

A

Energy released when a gaseous atom/molecule/ion in its ground state gains an electron

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11
Q

give some properties of ionic bonding

A

complete electron transfer from electropositive element to electronegative leaving both elements with a full shell. purely electrostatic bonding force, not conductive, high melting points

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12
Q

give some properties of metallic bonding

A

each atom completely looses one or more electron and turns into a positive ion, the electrons become delocalised between the ions, conduct heat and electricity, ductile , high melting point

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13
Q

What is pauli exclusion principle

A

No two electrons can have the same quantum numbers

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14
Q

What happens to coulombic energy as R reaches infinity

A

as r goes towards infinity, columbic energy reaches 0 as the further away the ions, the less attractive force between them

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15
Q

What happens to the coulombic energy as r reaches 0

A

as r reaches 0, coulombic energy reaches infinity as the ions are close together so strongly attracted

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16
Q

What is the Madelung constant and what does the Madelung constant depend on

A

shows net attractive energy between all ions in solid
depends on 3D arrangement of the ions

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17
Q

How do you find wavelength from energy?

A

wavelength = planks x speed of light/ energy

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18
Q

What units will the total energy from born-mayer potential equation be in

A

joules per mole

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19
Q

What is a glide plane

A

translation of motif halfway across unit cell then motif reflection

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20
Q

How are lattice enthalpy and total energy related

A

lattice enthalpy = -Total energy

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21
Q

Why is enthalpy often used over internal energy

A

enthalpy defined at a constant pressure

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22
Q

Why is change in H often the same as change in U

A

DeltaH=DeltaU x pDeltaV but as volume rarely changes pDeltaV is often 0 so DeltaH=DeltaU for solid state reactions

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23
Q

What is the first law of thermodynamics

A

energy cannot be created or destroyed

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24
Q

What does a negative/ positive enthalpy value mean

A

negative H means exothermic reaction so heat is flowing out of reaction. if H is positive its an endothermic reaction as heat is put into reaction

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25
Why is Kapustinskii's equation useful
this equation requires no knowledge of the structure of the compound so can be used in combination with born haber cycles
26
What is a unit cell
smallest repeating unit in a crystal
27
What is a lattice vector
shortest vector from one unit cell to the next (includes magnitude and direction)
28
what is a lattice point
a point in each repeating unit which represents the unit, they have identical environments in every respect
29
How many lattice vectors does a 3D crystal have
3 lattice vectors
30
What is the motif of a crystal structure
is the atom/group of atoms associated with the lattice point
31
What is crystal lattice
periodic arrangement of lattice points
32
what is crystal structure
crystal structure = crystal lattice x motif
33
What is a primitive unit cell
cube with lattice point in each corner but only 1/8th of each in unit cell giving 1 motif per unit cell
34
What are the 2 types of non-primitive unit cells
body centred cubic and face centred cubic
35
explain body centred cubic unit
same as primitive unit with extra lattice point in middle of cube, therefore has 2 lattice points inside the unit
36
explain face centred cubic
primitive unit with extra lattice point on every face, so has 4 lattice points inside the unit
37
What are the three types of symmetry a crystal cane have
translational, point group and combined point group translational symmetry
38
What are the 2 types of packing
hexagonal close packing and cubic close packing
39
What is a crystal system
there are 7 crystal system shapes all categorised by their symmetry properties. all different shapes of block that fill all space
40
What is a Bravais lattice
the 14 different ways the 7 crystal systems can be stacked uniquely. based on translational symmetry and defines how the units are repeated in space
41
Why is it important to consider tessellation
because when making a surface you dont want any gaps or overlaps between the geometric shapes. some shapes can tessellate and some cant.
42
What are the three rules of close packing of spheres (Think as 2D)
all atoms though of as hard spheres which have a particular radius and no distortion, the spheres are packed as tightly as possible and if different size spheres involved the big ones pack together and small ones fill the gaps
43
describe HCP
unit cell is an hexagonal prism, each atom has coordination number of 12 (6 on its own plane, 3 above and three below)
44
describe CCP (fcc)
ABCABC layering so no hollows, atoms have coordination number of 12
45
What is polymorphism
where a material has different crystal structures under different experimental conditions
46
What is the difference between a tetrahedral and octahedral hole
tetrahedral holes form between 3 A layer atoms and 1 B layer atom, the atoms have coordination number of 4 octahedral holes from between 3 A layer atoms and 3 B layer atoms forming a hexagon like ring with hollow in middle, atoms in this have coordination number of 6
47
how do waves interact with matter to give diffraction patterns
Diffraction occurs when a wave encounters an obstacle/opening and the wave bends around it creating an interference pattern. When waves encounter matter they scatter, the scattered waves overlap destructively and constructively leading to patterns showing maxima (constructive) and minima (destructive)
48
What is the general equation of a wave
y= A x sin(vx + Phi) where A=amplitude and v=frequency and Phi=phase shift
49
what determines whether waves will constructively overlap or destructively overlap
their phases, by looking at their phase shift (Phi)
50
What is the bragg equation?
n(Gamma)=2dsin(theta) where n=order of diffraction, Gamma=wavelength, d=layer spacing of diffracting layers, Theta=angle of incidence/angle of diffraction O aim by using is often to find d
51
how do you find separation for cubic systems using miller indices
d(hkl)=a/square root(h2+l2+k2) where a=length of side of unit cell cube (cubic lattice constant)
52
What is powder X-Ray diffraction used for
to find out which Bravais lattice a crystal has, and the size of unit cell
53
What is the difference between powder diffraction and single crystal diffraction
powder diffraction gives rings as there are many random orientations in the powder and the single crystal gives diffraction spots as a single crystal only has 1 orientation
54
What part of powder diffraction represents the motif of the crystal
the diffraction beam intensities relate to the motif
55
What do the position of the spots and the intensity relate to
the position of the spots in a diffraction pattern relate to the Bravais lattice, the intensity is related to the motif
56
What is the phase problem
the experiment measures intensity but what we actually need is the amplitude which contains both direction (phase) and magnitude. Intensity=square root of amplitude but square rooting looses the phase information where most the information lies
57
What are the general 2 ways X-Rays can be produced
by discrete transition from one energy level to another in an atom, or when a free electron(or any charged particle) is accelerated/decelerated (bremsstrahlung)
58
how does an X-Ray anode tube work to make xrays
electrons strike into metal target accelerated by high voltage which kick out core levels making higher energy electrons to fil these core holes. this process emits a photon with a characteristic wavelength, emission peaks. may electrons will instead be slowed down by increments on metal surfaces producing bremsstrahlung
59
How do synchrotrons work to produce xrays
Charged particles taken near the speed of light and crashed into another particle/target then put into a circular array of magnets to bend pathway with freq boosters to speed them up. insertion devices that are magnets with alternating parity which form the X-Ray wave
60
what is a free electron laser and how does it work t produce xrays
a long straight insertion device where electrons are injected into. Electrons will start to interact with strong EM field of produced light stimulating more intense and coherent emission called free electron lasers
61
why do we want to monochromate our light
if we have a range of wavelengths (Gamma) then we will not be able to be as precise in our measurement of d in Braggs equation
62
what 2 principles do monochromators use to work
they operate on 2 principles, diffraction and distance to tune wavelengths.
63
explain how monochromators manage diffraction
a single nearly perfect crystal used and orientated in a way to match the angle of incidence to wavelength through braggs equation. an identical crystal placed above to redirection the light into same direction
64
explain how monochromators take distance into account
sample placed at a distance from the monochromator so that any additional diffraction spots will spread out in diff directions and not hit your sample
65
What are the 2 kinds of neutron sources
nuclear reactors and spallation sources
66
how do nuclear reactors create neutrons
fission creates a large number of high energy neutrons which can be slowed down to thermal temps for use
67
how do spallation sources create neutrons
particle accelerators used to bombard heavy metals with highly energetic protons which excite nucleus which looses energy by emitting neutrons
68
What is resistance measured in
Ohms (W)
69
how is resistance related to conductance
C=1/R measured in siemens (s)
70
What is resistivity measured in and why is it an inherent property
Ohm metres, inherent as doesnt depend on size of object
71
What is conductivity (sigma)
sigma= 1/resistivity (p) also an inherent property, measured in S m-1
72
how do you work out resistance
lenth/conductivity x cross section of wire
73
Explain how resitance varies
the more conductive a material, the less resistant. the larger the cross sectional area the more space it has to conduct over so less resistant. the longer length it has to go over the more resistive the material it has to pass through
74
give the range of conductivity for conductors and give explanation of structure of of conductors
10^6 to 10^8 S.m^-1 electrical conductors consist of cations embedded in sea of electrons. free electrons carry electron density from negative to positive.
75
What happens to conductivity of a conductor as temp increases
as temp increases the conductivity decreases as the resistance of the material increases with temperature as the cation cores vibrate more which get in the way
76
give the range of conductivity for semiconductors. what happens to conductivity of semiconductors on increase of temp
10^-4 to 10^5 S.m^-1 as temp increases semiconductors conductivity increases due to electrons being excited from valence band into conduction band increasing exponentially.
77
give the range of conductivity for insulators. what happens to insulators at high temps
less than 10^-4 S.m^-1 at high temps the conductivity on an insulator will rise to region of semiconductors as insulators are semiconductors with a large band gaps.
78
Name the two band theories
nearly free electron model and LCAO theory
79
explain the origin of energy bands in solid materials and what does band gap determine
energy range where no electron states can exist (Nodes) due to the pauli exclusion principle. size of band gap determines electrical properties of material
80
What is a fermi level
defined as being half way up the band gap
81
Where do electrons occupy in semiconductors
the electrons completely and exactly fill the valence band but leave the conduction band completely empty and in between them lies the band gap where no orbitals exist at all.
82
What is density of states
the number of orbitals (states) there are per eV, per atom, in the band structure
83
Why does graphite conduct but diamond doesnt
due to the LCAO theory: they have different hybridisations. Diamon has sp3 hybridisation ut graphite has sp2 hybridisation and each hybridisations have different size HOMO LUMO gap sp3 has a large sigma-sigma star energy difference but graphite has a smaller pi-pistar energy difference so the band gap for diamond will be a lot larger than graphite
84
what are intrinsic semiconductors
ultra pure materials which follow valence band with bang gap and conduction band.
85
what are extrinsic semiconductors
deliberately made impure by embedding foreign atoms in the crystal to change electrical properties. often doping of silicon with phosphorus or silicon
86
what are the 2 types of extrinsic semiconductors
n-type and p-type
87
what are n-type semiconductors
(negative conductors meaning extra electron) mixed phosphorus into silicon crystal so some Si atoms replaced with P atoms, energy level of P atom lies just below the bottom of conduction band as P has 5 valance e rather than 4 so the 5th electron is excited thermally into conduction band
88
what are p-type semiconductors
(positive conductors meaning missing an electron) mixed aluminium into silicon crystal so some Si atoms replaced with Al. Al only has 3 valence electrons compared to Silicon's 4 so an electron is excited thermally from valence band onto the Al acceptor level. hole left in valence band can move to carry charge
89
Why are metals opaque and shiny
all due to behaviour of their free electrons, there is no band gap in in metals so no matter energy of radiation, there is a filled and empty level that corresponds exactly to photon energy. so all wavelengths are absorbed and all photons are immediately re-emitted
90
Why are semiconductors opaque to visible light but not IR
IR photons have smaller energies which arent enough to excite an electron into an orbital in conduction band so will be transparent but Vis photons will have enough energy to excite the electron into conduction band
91
why are insulators transparent and why do they have nice colours?
band gaps in insulators are larger than the photon energy of visible light so visible light will not be absorbed making them transparent but if the band gaps not too big, photon energies will be absorbed and the ones that arent will show as the coloured solid

CHEM2017 - Physical Chem (5 decks)

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