Hydrogen Bond
Hydrogen A Primarily electrostatic force of attraction btwn a hydrogen atom which is
covalently bound to more electronegative atom which is H bond donor and another
Hydrogen Gas electronegative atom bearing a lone pair of e-, H bond acceptor
A Low melting and boiling point due to weak intermolecular forces
A High bond enthalpy and short bond length Strength of H bonds
↳ not very reactive A Strongest when D and A are 2nd row elements (N,O or F)
requires catalyst for chemical rxns D Other atoms can act as D and A as long as they are more electronegative than H
↳ can undergo radical chain rxns once given Ea * C is slightly more electronegative than H so C-H bonds are poor H bond donors but
A Low density weak H bonds possible, especially when C bonded to electronegative atoms
A Escapes atmosphere because its light, gas has to be produced A Filled orbital such as pi bond can act as weak A and interact with H bond donor
Produced by steam reforming or water electrolysis I Group 14: increase in m.p. and b.p. as group is descended due to increase in relative
↳ Process is energy intensive (expensive), if fossil fuels used, high molecular mass which leads to increased dispersion interactions
carbon footprint (use renewable energy sources) Group 17: show similar trend from 2nd member on. In case of 1st member, all much
more electronegative than H and have lone pairs that can act as D
Uses
* Hydrogenation: preparation of drugs, fragrances etc Classes of Hydrides:
* Synthesis from syngas (H2 and CO): methanol, fuels etc * Molecular (covalent) hydrides - individual molecules, usually formed w/ p-block
A Synthesis of hydrogen peroxide elements of similar electronegativity
* Synthesis of ammonia (Haber process) A Saline (ionic) hydrides: usually formed w/ electropositive elements: non-volatile,
* Energy: fuel cells non-conducting, crystalline
A Metallic hydrides: non-stoichiometric, electrically conducting solids If and d-block)
Hydrides
A Binary compounds of hydrogen and H- Sub-classes of Covalent Hydrides:
A H bonded to a less electronegative element is hydric A E- precise compounds - all valence e- of central atom involved in bond forming
* E- rich compounds - not all e- on central atom involved in bonding, lone pairs
(oxid state of -1) E- deficient compounds - not possible to draw using 2-centre 2-e bonds
A H bonded to more electronegative atom, bond polarised,
with partial positive charge on H, H described as protic and can act as Lewis acids
(oxid state of + 1)
A Ionisation energy is very high, difficult to produce H AAs electronegativity of atom bonded to H, changes from hydride to protic so
ion, therefore protic hydrides are covalent becomes more acid across period
* Bonded to elements w/ similar electronegativity, bonding * Enthalpies of X-H bonds increase across period, due to increased overlap btwn
w/ H is non-polar, small partial charges can form orbitals and increase in ionic character of bonds
A Hydrides become less stable down a group, valence orbitals get larger and more
diffuse
, Acidity Lewis Theory
A Acid is an electron pair acceptor
Bronsted-Lowry exhibt Lew is acidity
-
↳ Has an acid centre with a relatively high formal positive
A Acid is a compound that donates a proton charge and at least one available, empty orbital
A Base is a compound that accepts a proton ↳ Has an acid centre w/ a coordination number less than
the maximum
B-L Conjugare
base acid
A Base is an electron pair donor
HCIE NHut Cl
-
NH3 + + ↳ Has a base centre w1 at least one available pair of
B- L Conjugate electrons
acid base
* Molecule w/ incomplete octet of valence electrons can complete octet by
accepting an electron pair
A Complex formation is exothermic as there is a net lowering in energy
when bond forms
Examples of Lewis Acid/Base
11 Molecule w/ a complete octet can rearrange its valence electrons 3) Ligand displacement reaction:
to accept an additional electron pair 2 .
.
9 CO2
g
i + Her
=R 4) Metathesis reaction:
H
2) A molecule or ion can expand its valence shell to accept
another e- pair e.g. Group 14 (not C) exhibit hypervalency
* Displacement driven by formation of another complex
A AgI is more favourable complex than AgBr
* If carried out in aqueous solution, further assisted by fact that
A Important factor is sterics: 3rd period are larger and AgI is less soluble in water
accommodate more than 4 atoms at bonding distance
4) Greater degree of coordination and exhibit hypervalency
,General Hydrides Coordination Chemistr
A Known as alkali metals - react w/ water to * Strongly basic and react quickly w/ water Crown ethers complex alk
give alkaline solutions * H- displaces OH-, stronger base * Smaller 2.2.1 ligand fa
A Very reactive: readily form compounds * Reactivity increases down the group D larger 2.2.2 cryptand
with 1 oxi state
t
A Handled under inert atmosphere, react w/ moisture in air
* Pyrophoric, fires hard to put out, inert materials used to Hydroxides
Elemental Form put out A React w/ water to form
I
A All have ns config * Na and K hydroxides are
* All soft, low melting metals that are conductors * Become less stable going down group produced on large scale
A Each atom contributes 1 e- to molecular orbital * Going down group, valence orbitals get larger and 2NaClinal + 2H20 , 11 - >
LD molecular bond is weak more diffuse A All group 1 hydroxides so
* Increase in atomic radii from Li to Cs results in decrease L Interactions of ns orbitals with 1s orbital of H are React w/ CO2 from air t
in first ionisation energy as you go down the group reduced 2MOH1aq) + 102(a) >
-
M2
47 Valence shell gets further away from nucleus * First ionisation energy is low, metals are all reactive and
A Large, -ve standard potentials, very easily oxidised form M ions more easily down group
t
Oxoanions
A Form salts with most ox
Oxides Useful reagents for making other hydride compounds
* Group 1 metals react rapidly w/ oxygen A Metathesis rxn w/ halides: Alkali carbonates
A Depending on element, range of oxides feasible GNGH + 2BF3 - BeHo + GNaF * Industrially important c
Lis Use lattice enthalpies to anticipate type of oxide Na , CO3 and NAHCOz
produced by combustion and stability of peroxides * As a strong base: I ↓
and superoxides NaHiss + CHyOHlet) >
-
NaOCHy + Ha production used in baki
A In general, large anions stabilised better by large cations of glass add CO2 to
heated w/
Only Li reacts directly w/ excess of O2 to give normal oxide:
4 Lis + 821as +
ILiz8iss
Group 1 silica to give Naz0 xSi0z
2 NaHCOs >
-
.
NazCOs + H20 +
Na react with O2 to give peroxide:
[Naci +
821q 1
>
-
Naz02 is Ozonides Organometa
Other group 1 elements form superoxides: A All group 1 elements form ozonides, contain Group 1 form m
k , x + 02(a) +
KO2(9) ozonide ion, 8 ,
-
A Chemically
A K, Rb and Cs ozonides prepared by heating peroxide or D Unstable in
A All oxides are basic and react w/ water to give OH- by superoxide with ozone (83) * Pyrophoric
t
extraction of H from water * Li and Na ozonides prepared by ion exchange with CsO3 D Handle unde
Liz0iss +
H20c >
-
[hitcags + 20Hsags in liquid ammonia
Naz82 + He011) >
-
[Nat + 20H-cags + HeO21ag A If burned in atmosphere w/ limited amount of O, Rb * Organolithiu
- +
, Elemental Form Hydrides
2
* All have config of ns A All but Be react w/ H to form hydrides
* Atomic radii is smaller than group 1 Ba + H2 >
-
Batte
General UT Higher densities and higher I.Es than group 1 A CaH2 and other heavier hydrides are ionic,
A Known as alkaline earth metals * Going down group, I.Es decrease, can more easily crystalline compounds
27
* All very reactive and form compounds form M A BeH2 and MgH2 have mainly covalent character
with oxi state of 2 t
* Compared to group 1, have higher mpts and are L Be and Mg have highest I.Es: more difficult
(mechanically) harder to convert to cations
↳ Directly related to stronger metallic bonding Li Have highest electronegativities
bc more e- involved A All but BeH2 react rapidly with water to release H
Late iss + 2H20 , ) >
-
Caltzcag) + 2 He (a)
D BeH2 reacts slowly w/ H2O but rapidly w/ acids
Halides Halides of heavier group 2 metals
Synthesis * Crystallise in ionic lattices Beryllium Hydride
* Can be synthesised from elements * Colourless, crystalline solids w/ fluorides * Prepared by thermal decomp of Be alkyls It Buz Be
A Colourless solid insoluble in solvents that dont decompose it
I
M(s) + x2 >
-
MXz melting much higher than others
A Alternative routes used industrially: LIT Exception: BeF2 forms glass A Covalent bonds
Be0 + (12 + C >
-
BeC12 + Co A Most chlorides, bromides and iodides are
deliquescent: SrBr2 is hygroscopic Structure: Three-dimensional network of linked BeH4 tetrahedr
Beryllium chloride
A Crystallises in polymeric strands w/
dative C1 Be -
>
Group 2
Hydroxides
Reaction with water Chemistry of Be(OH)2
A Be does not react due to passivation * Prepared by precipitation rxn
A Mg reacts w/ hot water or steam, slowly due BeCIz + NadHings >
-
BelOH(ciss + INaCling
to passivation A In excess oh (OH)- anions, forms water soluble complex anion
* Ca and other react w/ cold water: reactivity Be(OH)2(ss + 20H-sags >
-
[BelOHic]" lag) act as Lewis acid
increases down group * In rxn w/ sulphuric acid it is neutralised
Miss + 2H20(1 >
-
MglOHlecags Hasa Be(OH)2 iss + 2HeSO41ag1 >
-
BeSOuIss + 2H2Olags actas Brynsted base
* *
Hydrogen A Primarily electrostatic force of attraction btwn a hydrogen atom which is
covalently bound to more electronegative atom which is H bond donor and another
Hydrogen Gas electronegative atom bearing a lone pair of e-, H bond acceptor
A Low melting and boiling point due to weak intermolecular forces
A High bond enthalpy and short bond length Strength of H bonds
↳ not very reactive A Strongest when D and A are 2nd row elements (N,O or F)
requires catalyst for chemical rxns D Other atoms can act as D and A as long as they are more electronegative than H
↳ can undergo radical chain rxns once given Ea * C is slightly more electronegative than H so C-H bonds are poor H bond donors but
A Low density weak H bonds possible, especially when C bonded to electronegative atoms
A Escapes atmosphere because its light, gas has to be produced A Filled orbital such as pi bond can act as weak A and interact with H bond donor
Produced by steam reforming or water electrolysis I Group 14: increase in m.p. and b.p. as group is descended due to increase in relative
↳ Process is energy intensive (expensive), if fossil fuels used, high molecular mass which leads to increased dispersion interactions
carbon footprint (use renewable energy sources) Group 17: show similar trend from 2nd member on. In case of 1st member, all much
more electronegative than H and have lone pairs that can act as D
Uses
* Hydrogenation: preparation of drugs, fragrances etc Classes of Hydrides:
* Synthesis from syngas (H2 and CO): methanol, fuels etc * Molecular (covalent) hydrides - individual molecules, usually formed w/ p-block
A Synthesis of hydrogen peroxide elements of similar electronegativity
* Synthesis of ammonia (Haber process) A Saline (ionic) hydrides: usually formed w/ electropositive elements: non-volatile,
* Energy: fuel cells non-conducting, crystalline
A Metallic hydrides: non-stoichiometric, electrically conducting solids If and d-block)
Hydrides
A Binary compounds of hydrogen and H- Sub-classes of Covalent Hydrides:
A H bonded to a less electronegative element is hydric A E- precise compounds - all valence e- of central atom involved in bond forming
* E- rich compounds - not all e- on central atom involved in bonding, lone pairs
(oxid state of -1) E- deficient compounds - not possible to draw using 2-centre 2-e bonds
A H bonded to more electronegative atom, bond polarised,
with partial positive charge on H, H described as protic and can act as Lewis acids
(oxid state of + 1)
A Ionisation energy is very high, difficult to produce H AAs electronegativity of atom bonded to H, changes from hydride to protic so
ion, therefore protic hydrides are covalent becomes more acid across period
* Bonded to elements w/ similar electronegativity, bonding * Enthalpies of X-H bonds increase across period, due to increased overlap btwn
w/ H is non-polar, small partial charges can form orbitals and increase in ionic character of bonds
A Hydrides become less stable down a group, valence orbitals get larger and more
diffuse
, Acidity Lewis Theory
A Acid is an electron pair acceptor
Bronsted-Lowry exhibt Lew is acidity
-
↳ Has an acid centre with a relatively high formal positive
A Acid is a compound that donates a proton charge and at least one available, empty orbital
A Base is a compound that accepts a proton ↳ Has an acid centre w/ a coordination number less than
the maximum
B-L Conjugare
base acid
A Base is an electron pair donor
HCIE NHut Cl
-
NH3 + + ↳ Has a base centre w1 at least one available pair of
B- L Conjugate electrons
acid base
* Molecule w/ incomplete octet of valence electrons can complete octet by
accepting an electron pair
A Complex formation is exothermic as there is a net lowering in energy
when bond forms
Examples of Lewis Acid/Base
11 Molecule w/ a complete octet can rearrange its valence electrons 3) Ligand displacement reaction:
to accept an additional electron pair 2 .
.
9 CO2
g
i + Her
=R 4) Metathesis reaction:
H
2) A molecule or ion can expand its valence shell to accept
another e- pair e.g. Group 14 (not C) exhibit hypervalency
* Displacement driven by formation of another complex
A AgI is more favourable complex than AgBr
* If carried out in aqueous solution, further assisted by fact that
A Important factor is sterics: 3rd period are larger and AgI is less soluble in water
accommodate more than 4 atoms at bonding distance
4) Greater degree of coordination and exhibit hypervalency
,General Hydrides Coordination Chemistr
A Known as alkali metals - react w/ water to * Strongly basic and react quickly w/ water Crown ethers complex alk
give alkaline solutions * H- displaces OH-, stronger base * Smaller 2.2.1 ligand fa
A Very reactive: readily form compounds * Reactivity increases down the group D larger 2.2.2 cryptand
with 1 oxi state
t
A Handled under inert atmosphere, react w/ moisture in air
* Pyrophoric, fires hard to put out, inert materials used to Hydroxides
Elemental Form put out A React w/ water to form
I
A All have ns config * Na and K hydroxides are
* All soft, low melting metals that are conductors * Become less stable going down group produced on large scale
A Each atom contributes 1 e- to molecular orbital * Going down group, valence orbitals get larger and 2NaClinal + 2H20 , 11 - >
LD molecular bond is weak more diffuse A All group 1 hydroxides so
* Increase in atomic radii from Li to Cs results in decrease L Interactions of ns orbitals with 1s orbital of H are React w/ CO2 from air t
in first ionisation energy as you go down the group reduced 2MOH1aq) + 102(a) >
-
M2
47 Valence shell gets further away from nucleus * First ionisation energy is low, metals are all reactive and
A Large, -ve standard potentials, very easily oxidised form M ions more easily down group
t
Oxoanions
A Form salts with most ox
Oxides Useful reagents for making other hydride compounds
* Group 1 metals react rapidly w/ oxygen A Metathesis rxn w/ halides: Alkali carbonates
A Depending on element, range of oxides feasible GNGH + 2BF3 - BeHo + GNaF * Industrially important c
Lis Use lattice enthalpies to anticipate type of oxide Na , CO3 and NAHCOz
produced by combustion and stability of peroxides * As a strong base: I ↓
and superoxides NaHiss + CHyOHlet) >
-
NaOCHy + Ha production used in baki
A In general, large anions stabilised better by large cations of glass add CO2 to
heated w/
Only Li reacts directly w/ excess of O2 to give normal oxide:
4 Lis + 821as +
ILiz8iss
Group 1 silica to give Naz0 xSi0z
2 NaHCOs >
-
.
NazCOs + H20 +
Na react with O2 to give peroxide:
[Naci +
821q 1
>
-
Naz02 is Ozonides Organometa
Other group 1 elements form superoxides: A All group 1 elements form ozonides, contain Group 1 form m
k , x + 02(a) +
KO2(9) ozonide ion, 8 ,
-
A Chemically
A K, Rb and Cs ozonides prepared by heating peroxide or D Unstable in
A All oxides are basic and react w/ water to give OH- by superoxide with ozone (83) * Pyrophoric
t
extraction of H from water * Li and Na ozonides prepared by ion exchange with CsO3 D Handle unde
Liz0iss +
H20c >
-
[hitcags + 20Hsags in liquid ammonia
Naz82 + He011) >
-
[Nat + 20H-cags + HeO21ag A If burned in atmosphere w/ limited amount of O, Rb * Organolithiu
- +
, Elemental Form Hydrides
2
* All have config of ns A All but Be react w/ H to form hydrides
* Atomic radii is smaller than group 1 Ba + H2 >
-
Batte
General UT Higher densities and higher I.Es than group 1 A CaH2 and other heavier hydrides are ionic,
A Known as alkaline earth metals * Going down group, I.Es decrease, can more easily crystalline compounds
27
* All very reactive and form compounds form M A BeH2 and MgH2 have mainly covalent character
with oxi state of 2 t
* Compared to group 1, have higher mpts and are L Be and Mg have highest I.Es: more difficult
(mechanically) harder to convert to cations
↳ Directly related to stronger metallic bonding Li Have highest electronegativities
bc more e- involved A All but BeH2 react rapidly with water to release H
Late iss + 2H20 , ) >
-
Caltzcag) + 2 He (a)
D BeH2 reacts slowly w/ H2O but rapidly w/ acids
Halides Halides of heavier group 2 metals
Synthesis * Crystallise in ionic lattices Beryllium Hydride
* Can be synthesised from elements * Colourless, crystalline solids w/ fluorides * Prepared by thermal decomp of Be alkyls It Buz Be
A Colourless solid insoluble in solvents that dont decompose it
I
M(s) + x2 >
-
MXz melting much higher than others
A Alternative routes used industrially: LIT Exception: BeF2 forms glass A Covalent bonds
Be0 + (12 + C >
-
BeC12 + Co A Most chlorides, bromides and iodides are
deliquescent: SrBr2 is hygroscopic Structure: Three-dimensional network of linked BeH4 tetrahedr
Beryllium chloride
A Crystallises in polymeric strands w/
dative C1 Be -
>
Group 2
Hydroxides
Reaction with water Chemistry of Be(OH)2
A Be does not react due to passivation * Prepared by precipitation rxn
A Mg reacts w/ hot water or steam, slowly due BeCIz + NadHings >
-
BelOH(ciss + INaCling
to passivation A In excess oh (OH)- anions, forms water soluble complex anion
* Ca and other react w/ cold water: reactivity Be(OH)2(ss + 20H-sags >
-
[BelOHic]" lag) act as Lewis acid
increases down group * In rxn w/ sulphuric acid it is neutralised
Miss + 2H20(1 >
-
MglOHlecags Hasa Be(OH)2 iss + 2HeSO41ag1 >
-
BeSOuIss + 2H2Olags actas Brynsted base
* *
