Solid State Structures Flashcards

1
Q

which combination of cation/anion gives highest degree of polarisation/high covalent character?

A

small highly charged cations and large polarisable anions

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2
Q

large covalent character + Born-Landé equation

A

underestimates lattice energy (actual value obtained from a Born-Haber cycle = higher)

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3
Q

drawback of Madelung constant + interionic distance (r)

A

requires detailed knowledge of structure which may not be available

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4
Q

value of ‘k’ in Kapustinskii equation

A

107 900 pm kJ mol-1

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5
Q

predicting bond types - greater electronegativity

A

greater ionic character

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6
Q

predicting bond types - high electronegativity values

A

tends to be covalent

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7
Q

predicting bond types - low electronegativities

A

substance with be an alloy with metallic bonding

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8
Q

iodine

A

strong covalent bonds between atoms

weak intermolecular interactions

low mp/bp

sublimes with mild heating at atmospheric pressure

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9
Q

silicon

A

covalent network

each atom forms 4 covalent bonds

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10
Q

covalent network structures

A

infinite

atoms linked by covalent bonds

examples = boron, phosphorus + boron nitride

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11
Q

allotropy

A

elements that can form more than 1 structure

e.g. carbon (diamond, graphite, Buckminsterfullerene)

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12
Q

allotropes of tin

A

β tin (= white) - stable at rtp, metallic

α tin (= grey) - stable below 13°C, non-metallic

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13
Q

polymorphism

A

compounds that can also form more than 1 structure

e.g. quartz and β-cristobalite = polymorphs of SiO2

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14
Q

unit cell

A

smallest possible repeating unit for a structure

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15
Q

unit cell - vertex

A

1/8

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16
Q

unit cell - edge

17
Q

unit cell - face

18
Q

unit cell - body

19
Q

cell projection diagrams - 0 and 1 meaning

A

0 = bottom of cell
1 = top of cell

20
Q

interstitial sites

A

free space between spheres

21
Q

how many octahedral sites are there in cubic-close packing?

22
Q

how many tetrahedral sites are there in cubic-close packing?

23
Q

what is an alloy?

A

contains 2 or more metals or metal + non-metal

24
Q

why are alloys more commonly used than pure metals?

A

stronger - different sized atoms ∴ slide less easily

less susceptible to corrosion

25
substitutional alloys
atoms of 1 metal exchanged for those of another metal usually occurs when atoms are similar in size (alloy formation doesn't cause major distortions to lattice)
26
interstitial alloys
atoms of one metal are present in interstitial sites of another metal lattice
27
binary compounds
contains 2 elements close-packed structure (one element in interstitial sites) most ionic + some covalent described in this way
28
limiting radius ratio
smallest value of radius ratio - if radius is any smaller, cation-anion contact is lost
29
enthalpy change of formation
change in enthalpy when 1 mole of a compound is formed in a reaction between its elements in their standard states
30
enthalpy change of atomisation
change in enthalpy when 1 mole of an element is converted from solid to one mole of gas = 1/2 bond dissociation enthalpy
31
first ionisation energy
change in enthalpy when one mole of gas is converted to one mole of gaseous cations
32
electron gain enthalpy
change in enthalpy when 1 mole of gas is converted to 1 mole of gaseous anions = minus the e- affinity
33
lattice enthalpy
enthalpy change for conversion of 1 mole of ionic solid to gaseous ions = +ve
34
value for charge on electron
1.6022 x10^-19 C
35
value for permittivity of vacuum
8.8542 x 10-12 C2 J-1 m-1
36
polarisable
large anions - e- density is further from nucleus + less controlled small cations with higher charges - high charge density
37
kapustinskii equation
allows ionic radii for polyatomic ions to be estimated Madelung constant requires detailed knowledge of structure - may not be available
38
madelung constant
scale factor accounts for interactions in crystal -> cations + anions = attractive -> same charge = repulsive