Group 15 Flashcards
Describe the uses of phosphorus
- Surfactant
- Food additives
- Drug compounds
- Agro chemicals
- Non burning plastics
- Chemical weapons- white phosphorus
Describe group 15 elements
- Lewis bases
- Lone pair of electrons
- Electron rich
Which element is different to the other elements in the gorup
- Nitrogen- 2nd period
Why is Nitrogen unreactive
- Very strong triple bond- high bond dissociation enthalpy
- Large HOMO/LUMO gap -prevents oxidation/reduction
- Low polarisability- prevents attack by electrophiles of nucleophiles
How is N(V) accesible
- As nitrate NO3- ion
What is HNO3 used for
- Explosives, nylon and polyurethane
Why can phosphorus react with oxygen but is stable in water
- Unpaired electrons in oxygen are able to accept electron density so P attacks oxygen
List the N oxides
- N2O
- NO
- N2O3
- NO2
- N2O4
- N205
Describe relationship between N2O4 and N2O5
- Exist in equilibrium
- NO2 - Radical cation so combine
- N2O4- rapid resonancing
List important P oxides
- P4O10
2. P4O6
Describe P4O10
- P4 + 5O2 –> P4O10
- Phosphorus pentoxide
- Dehydrating agent
Describe P4O10 in water
- Acidic in water
2. P4O10 + 6H2O –> 4H3PO4
Describe P4O6 in water
- Acidic compound in water
- P4O6 + 6H2O –> 4H2PO3 phosphonic acid
- Source of acidity comes from OH
How are polyphosphoric acids formed
- H3PO4 + H3PO4 –> H2O + polyphosphoric acid
2. joined by O
Describe the halides of group 15
- AX3
2. Trigonal pyramidal- lone pair of electrons
Describe NF3
- Thermodynamically stable gas
- Does not react water, acids or alkalis
- Less basic than NH3
Why is NF3 less basic than NH3
- NF3 has polarised bonds
- Reduced lone pair activity
- So F removes e- from N
Describe NCl3
- Less polarisation –> more reactive
2. NCl3 + 3H2O –> NH3 + 3HOCl (Hypochlorous acid)
Describe NBr3/NI3
- More reactive
2. Weak bonds, diffuse halided, N-X poor overlap of orbitals
Describe PF3
- Gas
- Hydrolysed slowly in H2O, Faster in alkali
- PF3 + 3OH- –> H3PO3 + 3F-
- Binds to haemoglobin- toxic
Describe PCl3 reaction with water
- PCl3 + H2O –> H3PO3 + 3HCl
Compare reaction of PCl3 and NCl3 with water
- P-Cl more polarised - OH2 attacks P
2. N-Cl charge silimar - N lone pair attack H in H2O
Describe NF5
- Not known
2. N cannot achieve +5 oxidation state with halides
Describe PF5
- Gas
- Trigonal bipyramidal structure
- Expect to see 2 F signals in NMR
- Only observe one due to rapid axial/equatorial exchange- Berry Pseudorotation
Describe AsF5
- Similar PF5
Describe SbF5
- Liquid
- Sb is bigger so heavier unit so can accept e- density from F
- F bridges even in gas phase
- Cyclic tetramer-
5 increased coordination number - increased metallic character - Extended structures- atomic size
- Catenation- ring/chain formation
Describe SbF5 use as superacids
- SbF5 can accept X- leading to their use in super acids
2. SbF5 + 2HSO3F (fluorosulfonic acid) –> ‘SbF6’
What can superacids do
- Protonate methane
2. CH4 + H+ –>CH5+ –> H2 + CH3+ + 3CH4 –> C(CH3)3 + 3H2
Describe bp of NH3
- Hydrogen bonds raises the bp
Describe structure of BiF5
- Linear chains with trans-bridges
2. Too big to form a ring
Describe PH3–> Bih3
- Van der Waals forces only
- Weakening of the E-H bonds strength
- This weakening of E-H bond accounts for fact that PH5 does not exist
Compare PH5 to PF5
- PH5 –> PH3 + H2 -exothermic due to strong H-H bond
2. PF5 –> PF3 + F2 - weak due to e–e- repulsion- does not happen
What is the weakening of E-H bond caused by and what does it lead to
- Incompatible overlap of E and H orbitals
2. Decreasing bond strength leads to increasing acidity - easier release of H+
What does the poorer overlap of E-H orbitals down the group result in
- Long bonds as there is less e- - e- repulsion compared to NH3
What happens to the energy difference between S and P orbitals as you go down the group and what the consequences of this are
- It increases
- Less sp mixing
- Lone pairs held in orbitals close to nucleus- s-type –> lone pairs unavailable –> so heavy EH3 compounds are less basic- can’t abstract a proton
Compare PH3 and NH3 reactions to protons
- PH3- more likely to release H+
2. NH3- more likely to abstract H+
Describe allotropy and catenation of nitrogen
- N=- N - triple bond
2. Covalent gas
Describe allotropy and catenation of phosphorus
- 3 main forms
- 3 coordinate P, P-P single bonds
- White- chemical weapon, pyrophoric, small bond angle so wants to spring open and be oxidised
- Red- more dense, higher mp, less reactive, less strain- 2D polymer, still reactive-matches
- Black- stable, chair
Describe allotropy and catenation of As, Sb, Bi
- Adopt hexagonal sheet structures similar to black phosphorus
As you go down the groups 13,14,15 what happens to metallic character
- Covalent to metallic down the group
