Group 15

Question 1

Describe the uses of phosphorus

Answer 1

1. Surfactant
2. Food additives
3. Drug compounds
4. Agro chemicals
5. Non burning plastics
6. Chemical weapons- white phosphorus

Question 2

Describe group 15 elements

Answer 2

1. Lewis bases
2. Lone pair of electrons
3. Electron rich

Question 3

Which element is different to the other elements in the gorup

Answer 3

1. Nitrogen- 2nd period

Question 4

Why is Nitrogen unreactive

Answer 4

1. Very strong triple bond- high bond dissociation enthalpy
2. Large HOMO/LUMO gap -prevents oxidation/reduction
3. Low polarisability- prevents attack by electrophiles of nucleophiles

Question 5

How is N(V) accesible

Answer 5

1. As nitrate NO3- ion

Question 6

What is HNO3 used for

Answer 6

1. Explosives, nylon and polyurethane

Question 7

Why can phosphorus react with oxygen but is stable in water

Answer 7

1. Unpaired electrons in oxygen are able to accept electron density so P attacks oxygen

Question 8

List the N oxides

Answer 8

1. N2O
2. NO
3. N2O3
4. NO2
5. N2O4
6. N205

Question 9

Describe relationship between N2O4 and N2O5

Answer 9

1. Exist in equilibrium
2. NO2 - Radical cation so combine
3. N2O4- rapid resonancing

Question 10

List important P oxides

Answer 10

1. P4O10

2. P4O6

Question 11

Describe P4O10

Answer 11

1. P4 + 5O2 –> P4O10
2. Phosphorus pentoxide
3. Dehydrating agent

Question 12

Describe P4O10 in water

Answer 12

1. Acidic in water

2. P4O10 + 6H2O –> 4H3PO4

Question 13

Describe P4O6 in water

Answer 13

1. Acidic compound in water
2. P4O6 + 6H2O –> 4H2PO3 phosphonic acid
3. Source of acidity comes from OH

Question 14

How are polyphosphoric acids formed

Answer 14

1. H3PO4 + H3PO4 –> H2O + polyphosphoric acid

2. joined by O

Question 15

Describe the halides of group 15

Answer 15

1. AX3

2. Trigonal pyramidal- lone pair of electrons

Question 16

Describe NF3

Answer 16

1. Thermodynamically stable gas
2. Does not react water, acids or alkalis
3. Less basic than NH3

Question 17

Why is NF3 less basic than NH3

Answer 17

1. NF3 has polarised bonds
2. Reduced lone pair activity
3. So F removes e- from N

Question 18

Describe NCl3

Answer 18

1. Less polarisation –> more reactive

2. NCl3 + 3H2O –> NH3 + 3HOCl (Hypochlorous acid)

Question 19

Describe NBr3/NI3

Answer 19

1. More reactive

2. Weak bonds, diffuse halided, N-X poor overlap of orbitals

Question 20

Describe PF3

Answer 20

1. Gas
2. Hydrolysed slowly in H2O, Faster in alkali
3. PF3 + 3OH- –> H3PO3 + 3F-
4. Binds to haemoglobin- toxic

Question 21

Describe PCl3 reaction with water

Answer 21

1. PCl3 + H2O –> H3PO3 + 3HCl

Question 22

Compare reaction of PCl3 and NCl3 with water

Answer 22

1. P-Cl more polarised - OH2 attacks P

2. N-Cl charge silimar - N lone pair attack H in H2O

Question 23

Describe NF5

Answer 23

1. Not known

2. N cannot achieve +5 oxidation state with halides

Question 24

Describe PF5

Answer 24

1. Gas
2. Trigonal bipyramidal structure
3. Expect to see 2 F signals in NMR
4. Only observe one due to rapid axial/equatorial exchange- Berry Pseudorotation

Question 25

Describe AsF5

Answer 25

1. Similar PF5

Question 26

Describe SbF5

Answer 26

1. Liquid 2. Sb is bigger so heavier unit so can accept e- density from F 3. F bridges even in gas phase 4. Cyclic tetramer- 5 increased coordination number - increased metallic character 6. Extended structures- atomic size 7. Catenation- ring/chain formation

Question 27

Describe SbF5 use as superacids

Answer 27

1. SbF5 can accept X- leading to their use in super acids | 2. SbF5 + 2HSO3F (fluorosulfonic acid) --> 'SbF6'

Question 28

What can superacids do

Answer 28

1. Protonate methane | 2. CH4 + H+ -->CH5+ --> H2 + CH3+ + 3CH4 --> C(CH3)3 + 3H2

Question 29

Describe bp of NH3

Answer 29

1. Hydrogen bonds raises the bp

Question 30

Describe structure of BiF5

Answer 30

1. Linear chains with trans-bridges | 2. Too big to form a ring

Question 31

Describe PH3--> Bih3

Answer 31

1. Van der Waals forces only 2. Weakening of the E-H bonds strength 3. This weakening of E-H bond accounts for fact that PH5 does not exist

Question 32

Compare PH5 to PF5

Answer 32

1. PH5 --> PH3 + H2 -exothermic due to strong H-H bond | 2. PF5 --> PF3 + F2 - weak due to e--e- repulsion- does not happen

Question 33

What is the weakening of E-H bond caused by and what does it lead to

Answer 33

1. Incompatible overlap of E and H orbitals | 2. Decreasing bond strength leads to increasing acidity - easier release of H+

Question 34

What does the poorer overlap of E-H orbitals down the group result in

Answer 34

1. Long bonds as there is less e- - e- repulsion compared to NH3

Question 35

What happens to the energy difference between S and P orbitals as you go down the group and what the consequences of this are

Answer 35

1. It increases 2. Less sp mixing 3. 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

Question 36

Compare PH3 and NH3 reactions to protons

Answer 36

1. PH3- more likely to release H+ | 2. NH3- more likely to abstract H+

Question 37

Describe allotropy and catenation of nitrogen

Answer 37

1. N=- N - triple bond | 2. Covalent gas

Question 38

Describe allotropy and catenation of phosphorus

Answer 38

1. 3 main forms 2. 3 coordinate P, P-P single bonds 3. White- chemical weapon, pyrophoric, small bond angle so wants to spring open and be oxidised 4. Red- more dense, higher mp, less reactive, less strain- 2D polymer, still reactive-matches 5. Black- stable, chair

Question 39

Describe allotropy and catenation of As, Sb, Bi

Answer 39

1. Adopt hexagonal sheet structures similar to black phosphorus

Question 40

As you go down the groups 13,14,15 what happens to metallic character

Answer 40

1. Covalent to metallic down the group