non-metal chemistry Flashcards
(143 cards)
1
Q
What are non-metal characteristics
A
- entropy ~ gases/volatile liquids and solids
- electrical resistivity ~ typically insulators
- oxidising agents ~ electron acceptors
- molecular hydrides, oxides, and halides
- acids/bases ~ acidic oxides, but acidic/alkaline/neutral hydrides
2
Q
describe the structures that elemental boron forms
A
based on B12 icosahedral units (Ih symmetry)
different crystals form by the different ways of linking B12 units together
5-fold symmetry
alpha rhomohedral form is 37% efficient at space filling
3
Q
elemental boron exhibits ____
A
allotropy - several crystalline and amorphous forms
4
Q
define allotropy
A
refers to elements existing in two or more different forms, in the same physical state
5
Q
describe the structures adopted by metal borides
A
chains, layers, polyborides such as B6 units
6
Q
give some examples of metal borides
A
TaB2, CaB6, UB4
7
Q
how can you form boranes
A
MgB2 + H2O -> Boranes
8
Q
what are some uses of metal borides
A
armour, rocket nozzles etc (inert characteristics)
magnets (Nd2Fe14B)
9
Q
synthesis of BF3
A
Na2B4O7 + 6CaF2 + 8H2SO4 -> 2NaHSO4 + 6CaSO4 + 7H2O + 4BF3
10
Q
synthesis of BCl3
A
B2O3 + 3Cl2 + 3C -> 2BCl3 + 3CO
11
Q
Synthesis of BI3
A
NaBH4 + 2I2 -> BI3 + NaI + 2H2
12
Q
compare Al2Cl6 and BCl3
A
Al2Cl6 has weak intramolecular π bonding so forms a dimer
BCl3 has strong intramolecular π bonding so only forms a monomer
13
Q
BX3 + H2O
A
H3BO3 + 3HX (X=Cl,Br,I)
14
Q
what happens if you heat H2O-BF3 ?
A
H3O+ [BF3(OH)]- -> BF3 (g)
due to strong B-F bond
15
Q
2B + 3/2O2 -> ?
A
B2O3 <–> B(OH)3
(in aqueous conditions and heat)
16
Q
A
16
Q
how can you make borates? give an example
A
B2O3 + 3CaO -> Ca3(BO3)2
17
Q
B(OH)3 + ROH -> ?
A
B(OR)(OH)2 (borate esters) which decompose to give B(OR)2OH, B(OR)3
18
Q
B(OR)3 + LiR (then H2O) -> ?
A
RB(OH)2 (boronic acid)
19
Q
what are the properties of boron hydrides
A
- stability; all endothermic (thermally unstable) compounds => kinetic stability
- oxidation state < 3 => B-B bonding
- structure and bonding is complex, eg B2H6
- can act as reducing agents
20
Q
Synthesis of B2H6
A
3NaBH4 + 4BF3 -> 3NaBF4 + 2B2H6
(in presence of diglyme)
21
Q
describe the bonding in diborane
A
bridging bonds longer than bonds in terminal units
2-electron 3-centre bonding
22
Q
LiBH4 + BF3 ->
A
B2H6
23
Q
NaBH4 + I2
A
B2H6
24
B2H6 + 3O2 ->
B(OH)3
25
B2H6 + NMe3 ->
H3B<-NMe3
26
B2H6 + 6H2O ->
2B(OH)3 + 6H2
27
B2H6 + NH3 ->
BH4- + [(NH3)2 BH2]+
28
how can diborane form higher boranes
pyrolysis
29
Describe the structure of borazine
Planar B3N3 ring, all B-N bonds the same length
B=N is isoelectronic with C=C so borazine is like benzene
due to polarity, much more reactive than benzene
not a regular hexagon (bond angles and B-H vs N-H bonds not same length)
30
synthesis of borazine using BCl3
3BCl3 + 3NH4Cl -> 9HCl + B3N3H3Cl3
add HCl and NaBH4
gives borazine
31
synthesis of borazine using B2H6 or NaBH4
B2H6 + NH3 + heat -> borazine
NH4Cl + NaBH4 + heat -> borazine
both go via H3N->BH3
32
how can you form boron nitride
heating borazine
33
describe the structrure of boron nitride
hexagonal boron nitride forms a layered structure similar to graphite
B above N interlayer interaction
electrical insular because B-N polar bond means electrons are localised
34
how can hexagonal boron nitride from cubic boron nitride
high temperature and pressure
35
describe the properties and uses of cubic boron nitride
high thermal conductivity
excellent wear resistance
good chemical intertness
used for tool bits like diamond is
36
what are the uses of hexagonal boron nitride
ceramics, alloys, resins, plastics, rubbers, and other materials
gives them self-lubricating properties
37
what solid state structure is diamond closely related to
zinc blende (ZnS) structure
38
describe intercalation compounds of graphene
* atoms or molecules in between layers
* once the layer is open up, ions fill up this layer
* stoichiometry can be KC8, KC20 etc
* halogens also intercalate
* KC8 and C8Br are more conducting than graphite because K donates electrons to band structure and Hal accepts electrons producing electron holes
39
Describe the structure of C60 (which is a fullerene)
1. football like structure (12 pentagons and 20 hexagons)
2. all atoms equivalent
3. 2 distinct types of bond, C=C and C-C
3. solid is fcc lattice of C60 spheres
40
describe the properties of C60
magenta solid
magenta solution in benzene
single line in 13C NMR
41
describe the properties of C70
red-brown solid
red solution in benzene
5 resonances in 13C NMR
42
Describe the reactivity of C60
addition of K to make superconductor
OsO4 to make osmate esters
(Ph3P)2Pt(C2H4) to add Pt(Ph3)2 to double bond
Birch reduction using Li NH3 (l) and tBuOH producing C60H36
43
Give examples of carbides
CaC2, WC
44
acetylides contain ____ anions
C2 2- anions (isooelectronic with N2)
45
synthesis of CaC2
2CaO + 3C -> CaC2 + 2CO
at 1000 oC
46
CaC2 + 2CO + 2H2O ->
Ca(OH)2 + C2H2
47
synthesis of CF4
SiC + F2 -> CF4 + SiF4
48
SiF4 + NaOH (aq) ->
SiO2 + SiF6 2- etc
49
Synthesis of CCl4
CS2 + Cl2 -> CCl4 + S2Cl2
(in presence of Fe)
50
CCl4 + 4EtX4 + AlCl3 ->
CX4 + 4EtCl
51
Why is SiX4 unstable to hydrolysis whilst CX4 is inert
CX4: no vacant orbitals or lone pairs, carbon is small => inert
SiX4: Si-X bonds polar, Si is large, vacant 3d orbitals => reactive
## Footnote
hydrocarbons need a spark to ignite whereas silicon halids/hydrides will explode in oxygen
52
describe the properties of fluorocarbons
* high C-F bond energy ~ CF4 is extremely inert
* wide range of highly fluorinated analogues of hydrocarbons
* F vs H - both monovalent and small so minimal steric crowding
* F atoms are not very polarisable => weak intermolecular forces => high volatility and solubility
53
give a common useful compound which is a fluorocarbon
radical polymerised C2F2
teflon (polytetrafluoroethylene)
* chemically resistant
* hydrophobic
54
what are problems with chloroflurocarbons being released in the atmosphere
deplete stratospheric ozone by radical mechanism
also high global warming potential (act as a powerful greenhouse gas)
55
compare single and double bond strengths for Si and C
2B(E-E) > B(E=E) for both Si and C
56
compare single and double bond strengths with oxygen for Si and C
B(C=O) > 2B(C-O)
B(Si=O) < 2B(Si-O)
57
what are the acid/base properties of carbon oxides
CO and CO2 are both very weak acids
58
what is a use of supercritical carbon dioxide
coffee bean decaffeination
59
why do metal carbonyl complexes have strong bonds
π backbonding (eg dxy and CO antibonding π MO)
sigma bond between lone pair and dx2-y2
60
what are N accessible oxidation states
-3 -> +5
61
Compare BDE(P-P) with BDE(N-N)
BDE(P-P) > BDE(N-N)
however triple bond other way round
(think non-bonded repulsion)
62
Describe the properties of ammonia
colourless, poisonous gas with with a familiar noxious odour
63
what process is used for ammonia synthesis
haber-bosch process
64
synthesis of NO
4NH3 + 5O2 -> 4NO + 6H2O
1000 oC/Pt catalyst
65
synthesis of NO2
2NO + O2 -> 2NO2
66
syntheiss of HNO3
4NO2 + O2 + 2H2O -> 4HNO3
67
NH3 ->
Na/Fe3+
NaNH2 -> NaN3
N2O/heat
68
synthesis of NH3 (not haber-bosch)
Li3N + H2O -> NH3
69
NH3 ->
O2/Pt 1200 oC
NO * -> HNO3
O2/H2O
70
NH3 + CH4/O2 ->
HCN
71
NH3 + NaOCl ->
N2H4
72
NH3 + F2/Cu ->
NF3 + N2F4 * + N2F2 *
73
hydrazine synthesis
NH3 + NaOCl -> NH2Cl + NaOH
products above + NH3 + NaOH -> N2H4 + NaCl + H2O
| first step fast, second slow
74
what conformation of hydrazine is most stable
gauche (with lone pairs closest but not eclipsed)
75
what is a use of hydrazine, give an equation
N2H4 + O2 -> N2 + H2O
rocket fuel
76
synthesis of NF3
NH3 + F2 -> NF4+ F-
77
Synthesis of NCl3
NH4Cl + Cl2 -> NCl3
pH < 7
78
what are some properties of NCl3
thermally unstable
yellow oil
explosive
79
NBr3 / NI3 synthesis
NH3 + I2 (aq) -> NI3.8NH3
## Footnote
very unstable, not known free of ammonia
80
what is special about N(SiMe3)3 and Ni(SiH3)3
planar due to dπ -pπ bonding
81
describe the properties of N2F4
colourless toxic irritant gas
82
synthesis of N2F4
NH3 + F2 -> NF3 + N2F4 + N2F2
Cu cat
83
describe the structure of N2F4
gauche and trans isomers most stable (trans only more stable by 2 kJ/mol)
84
describe some issues with nitrides and give some examples
* nitrogen atoms in holes in metal structures
* 3 electron affinities require lots of energy (i.e. to make N(-3)) so need small cation to stabilise the structure
* only stable G1 nitride is Li3N
* only stable G2 nitride is Mg3N2
^ both ionic nitrides
85
describe the structure of lithium nitride (Li3N)
* Li+[Li2N]-
* contains hexagonal Li6 nets
* N has hexagonal bipyramidal coordination
* Li3N has high electrical conductivity
* layered structure
N in the middle of hexagons and joins layers with an intermediate Li+ ion (hence the formula at the top)
86
nitrous oxide, N2O
colourless, rather unreactive, laughing gas, sweet odour
87
nitrogen monoxide, NO
colourless, moderately reactive, simplest known thermally unstable paramagnetic molecule
88
dinitrogen trioxide, N2O3
dark blue, extensively dissociated as gas
89
Dinitrogen tetroxide, N2O4
colourless, exentively dissociated to NO2 as gas and partly as liquid
90
dinitrogen pentoxide, N2O5
colourless, unstable as gas; ionic solid
not well characterised and quite unstable
strong oxidiser which forms explosive mixtures with organic compounds and ammonium salts (decomp produces highly toxic dioxide gas)
91
nitrogen dioxide, NO2
brown gas, rather reactive
92
synthesis of N2O (dinitrogen monoxide)
NH4NO3 -> N2O + 2H2O
heat
93
synthesis of NO
2NaNO2 + 3H2SO4 + 3FeSO4 -> 2NO + Fe2(SO4)3 + 2NaHSO4 + 2H2O
or
3Cu + (dil) 8HNO3 -> 2NO + 4H2O + 3Cu(NO3)2
94
does NO form a dimer?
in a solid, forms a dimer
π /π * overlap gives long and weak N-N bond, diamagnetic (instead of paramagnetic on its own)
95
synthesis of dinitrogen trioxide, N2O3
2NO + N2O4 -> 2N2O3
N2O3 readily dissociates though:
N2O3 <-> NO + NO2
96
Structure of dinitrogen trioxide, N2O3
symmetric and asymmetric isomers
O=N-O-N=O (trigonal planar around each N)
O=N-NO2 (NO2 structures like nitro group) and trigonal planar around other N
97
Synthesis of Nitrogen Dioxide NO2
Pb(NO3)2 -> PbO + 2NO2 + 1/2 O2
2NO2 <-> N2O4
N2O4 is dimer of two NO2 molecules (trigonal planar around each N)
98
describe the structure of N2O5
two nitro groups joined by bridging O bond
99
what are the physical characteristics of oxygen
colourless gas
blue liquid
blue solid
100
what are the properties of ozone, O3
colourless gas
blue liquid
violet solid
absorbs harmful UV
produced in silent electrical discharge
ozone has a very sharp odour resembling chlorine bleach in air
very powerful oxidising agent
## Footnote
can produce headaches, burning eyes, irritation to respiratory passages
101
excited form of O2 has ____
paired π * electrons (singlet)
shows red chemiluminesence (emission of light)
102
why is liquid O2 blue
a single photon (in the red portion of the visible spectrum) excites two O2 molecules simultaneously
this transition is only observed in small amounts of oxygen gas at low pressures due to the low probability of a 3 body process
103
in what compound does [O2]+ exist
O2+PtF6-
104
compare the reactivity of coordinated O2 and free O2
coordinated O2 is much more reactive than free O2
105
how does O2 coordinate to metals
as O2-
106
what is special about H3Si-O-SiH3
angle > 150 o (in bent geometry)
due to π interactions
107
what is the geometry of [Cl5Ru-O-RuCl5]4-
linear
due to M(dπ) <- O(pπ) bonding
108
when are three-coordinate O compounds trigonal planar
in some OM3 groups eg when M=Cr
again as a result of pπ <- dπ bonding
109
solid state structure of M2O
anti-fluorite (Cs2O is layered anti-CdCl2 structure)
110
solid state structure of MO
rock salt structure (group 2 and many transition metal oxides)
111
solid state structure of M2O3
corundum structure ~ Al2O3 and transition metal oxides
112
solid state structure of MO2
fluorite (CaF2) and rutile (TiO2) structures
113
solid state structure of M3O4
Spinel structure ~ typically mixed valence
114
solid state structure of ABO3
perovskite and many other mixed oxide structures
115
periodic changes in nature of oxides
* across a period, Zeff increases, so bonding more covalent and localised => decrease in coordination number of element by oxygen
* down a group ionisation energy decreases, and size increases => elements become more metallic and bonding to oxygen more ionic
* higher oxidation state oxides are more covalent and more likely to contain E=O bonds
116
describe acid base properties of oxides
* highly ionic oxides (G1 and 2) basic
* highly covalent oxides (G14-17) are acidic
* amphoteric line moves further to right of period as groups are descended
* acidity increases with oxidation state for elements of variable oxidation state
## Footnote
concept of polarising power explains the trends
117
lab synthesis of hydrogen peroxide
BaO2 + H2SO4 (aq) -> BaSO4 + H2O2
118
describe the structure of hydrogen peroxide
"open-book" structure (not what VSEPR would predict)
119
appearance of fluorine
light yellow coloured gas
120
appearance of chlorine
greenish yellow gas
121
appearance of bromine
reddish brown liquid
122
appearance of iodine
violet solid
123
what is the origin of the colour of halogens
π * - σ * transition
down the group the separation of these orbital energies decreases (hence colour changes down group)
124
extraction of F2
electrolysis of KHF2
H2 produced at cathode and F2 at the anode
125
extraction of Cl2
electrolysis of NaCl/H2O -> NaOH + Cl2
126
extraction of Br2 and I2
by Cl2 oxidation of Br- and I-
2X- + 4H+ + MnO2 -> Mn2+ + H2O + X2
where X = Cl, Br, I
127
How can you get Hal2+ species
stability?
in non aqueous solvents
order of stability I > Br > Cl
I2/ conc. H2SO4 -> I2+ which is blue paramagnetic
Br2+[Sb3F16]- (Cl2+ analogue unstable at 20 oC)
128
what are the unique aspects of fluorine
* unexpectedly low BDE due to lone pair repulsion
* strong bonds to other elements (especially if π bonding to empty orbitals on E)
* valence expansion of combined elements (small size, space for high CN and highly oxidising so allows maximum oxidation state)
* high electronegativity so strong H bonding and large inductive effect
* small size of F- so high lattice energies and hydration energies
129
EF2 is unstable to ____
| halogen chem
disproportionation (eg SF2)
130
covalency increases ____
| halogen chem
down the series f -> I
with increasing oxidation state
131
synthesis of HX
CaX2 + H2SO4 -> CaSO4 + 2HX (X = F, Cl)
use H3PO4 for HBr and HI
132
anomalous properties of HF
* boiling point
* acid strength in aqueous solution
* strong acid in pure liquid state
133
all halogen oxides are ___
thermally unstable => reflects their kinetic stability
134
properties and use of hypochlorite ClO-
good oxidising agent, bleach
135
properties and use of chlorite, ClO2-
strong oxidising agent, disproportionates, water treatment
136
properties and use of chlorate, ClO3-
oxidising agent, fireworks/weed killer
137
properties and uses of perchlorate, ClO4-
oxidising agent and weak acid,
airbags
138
is there free X2 in acid or base conditions
no free X2 in alkali but free X2 in acid (roughly 50% Cl2 in chlorine water)
139
what are the species in equilibria in bleach
at alkaline/neutral pH ClO- is the active ingredient which is in equilibrium with Cl2O (gives the yellow colour of bleach)
140
what is a probem with ClO- in aqueous solution
further disproportionation to Cl- and ClO3-
141
NH3 + HOCl ->
NH2Cl + H2O
142
NHCl2 + HOCl ->
NCl3 + H2O
(NCl3 is explosive so this is not good - do not want excess HOCl in swimming pools)
