Group 13, 14, 15

Question 1

what do group 13 elements/halides act as?

Answer 1

[Lewis acids]
-empty p orbital
-electron poor
-6 valence e- -> want to accept e- from Lewis base to make stable octet

Question 2

BX3

Answer 2

monomeric

trigonal planar

more volatile than Al analogue

B-X bond length increases F -> I (anion gets weaker)

Question 3

why is L.BF3 less likely to form compared to L.BBr3 ?

Answer 3

B-X have 𝛑 character

sp2 hybridised

when “L” coordinates, the change in geometry (sp2 -> sp3) means 𝛑 interactions are now lost - endothermic reorganisation

L->B bond formation = exothermic

F = strongest stabiliser (smaller ∴ better overlap)

∴ bigger energy deficit on loss of B-F 𝛑 bond character

Question 4

organometallic chemistry of aluminium

Answer 4

Al2M6 (dimer)

volatile, reactive, liquid, flammable in air

similar to Al2Cl6 - no l.p/filled orbitals to donate e- density into Al empty p orbital (lower stability)

Question 5

halides

Answer 5

CF4, CCl4 = inert

SiCl4 = readily hydrolysed by water
SiCl4 + 2H2O -> SiO2 + HCl

Si = bigger than C - more prone to nucleophilic attack

Sn, Pb - EX2 more stable than EX4
especially Pb as it’s at bottom of group - inert pair effect

SnCl2 - reducing agent

SnCl4 - liquid (freezes at -33°C - molecular rather than ionic) + tetrahedral
less reactive than group I metals

Question 6

oxides - carbon

Answer 6

[CO]
-forms in limited O2 supply
-binds to Fe in haemoglobin - prevents oxygen -transport from lungs to cells

[CO2]
-water soluble

Question 7

lead

Answer 7

PbO2

strong oxidising agent
Pb(IV) = easily reduced to Pb(II)

**Tin behaves similarly

Question 8

group 15 - properties

Answer 8

lone pair

lewis base

e- rich

Question 9

important NO compounds

Answer 9

N2O, NO, N2O3, NO2, N2O4, N2O5

Question 10

important oxides of P

Answer 10

[oxidation states = +3, +5]

P4O6 - P(III)
-acidic
-P4O6 + H2O -> 4H3PO3

P4O10
-acidic
-P4O10 + 6H2O -> 4H3PO4

Question 11

phosphorus acids

Answer 11

[protons from OH = source of acidity - low pKa; easily released from oxygen]

H3PO3 = phosphonic acid
-diprotic
-tetrahedral

H3PO4 = phosphoric acid
-triprotic
-tetrahedral

Question 12

group 15 - halides (NX3)

Answer 12

[NF3]
-thermodynamically stable gas
-no reaction with water, acid or bases
-less basic than NH3

[NCl3]
-less polarisation - more reactive
-NCl3 + 3H2O -> NH3 + 3HOCl

[NBr3 + NI3]
-weaker bonds
-more reactive
-diffuse halide, poor orbital overlap

Question 13

group 15 - halides (PX3)

Answer 13

[PF3]
-gas
-hydrolysed in water
-reacts faster in alkali -> PF3 + 3OH- -> H3PO3 + 3F-
-binds to haemoglobin - toxic

[PCl3]
-PCl3 + H2O -> H3PO3 + 3HCl

Question 14

group 15 - AX5

Answer 14

[NF5]
-not known
-N can’t achieve +5 oxidation state with halides

[PF5 + AsF5]
-gas

[SbF5]
-liquid
-F bridges even in gas phase (Sb > As)
increased coordination number

Question 15

group 15 - H compounds

Answer 15

NH3 - hydrogen bonding raises b.p.

[PH3 -> BiH3]
-Van der Waals forces only
-weakening E-H bond strength

Question 16

group 15 - weak bonds

Answer 16

incompatible overlap of E and H1s orbitals decreases bond strength leads to increased acidity

poorer overlap of E-H orbitals decreases down group

results in long bonds

less e- repulsion compared to N-H

Question 17

group 15 - energy difference between s+p orbitals

Answer 17

[decreases]
-less s-p mixing
-lone pairs held in orbitals close to nucleus
-s-type = not available for bonding
-heavier EH3 are less basic (unable to abstract H+)
-PH3 = more likely to release H+
-NH3 = less likely to release H+