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CH10134 > Group 15 > Flashcards

Group 15 Flashcards

1
Q

Describe the uses of phosphorus

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

Describe group 15 elements

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

Which element is different to the other elements in the gorup

A
  1. Nitrogen- 2nd period
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4
Q

Why is Nitrogen unreactive

A
  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
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5
Q

How is N(V) accesible

A
  1. As nitrate NO3- ion
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6
Q

What is HNO3 used for

A
  1. Explosives, nylon and polyurethane
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7
Q

Why can phosphorus react with oxygen but is stable in water

A
  1. Unpaired electrons in oxygen are able to accept electron density so P attacks oxygen
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8
Q

List the N oxides

A
  1. N2O
  2. NO
  3. N2O3
  4. NO2
  5. N2O4
  6. N205
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9
Q

Describe relationship between N2O4 and N2O5

A
  1. Exist in equilibrium
  2. NO2 - Radical cation so combine
  3. N2O4- rapid resonancing
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10
Q

List important P oxides

A
  1. P4O10

2. P4O6

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11
Q

Describe P4O10

A
  1. P4 + 5O2 –> P4O10
  2. Phosphorus pentoxide
  3. Dehydrating agent
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12
Q

Describe P4O10 in water

A
  1. Acidic in water

2. P4O10 + 6H2O –> 4H3PO4

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13
Q

Describe P4O6 in water

A
  1. Acidic compound in water
  2. P4O6 + 6H2O –> 4H2PO3 phosphonic acid
  3. Source of acidity comes from OH
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14
Q

How are polyphosphoric acids formed

A
  1. H3PO4 + H3PO4 –> H2O + polyphosphoric acid

2. joined by O

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15
Q

Describe the halides of group 15

A
  1. AX3

2. Trigonal pyramidal- lone pair of electrons

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16
Q

Describe NF3

A
  1. Thermodynamically stable gas
  2. Does not react water, acids or alkalis
  3. Less basic than NH3
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17
Q

Why is NF3 less basic than NH3

A
  1. NF3 has polarised bonds
  2. Reduced lone pair activity
  3. So F removes e- from N
18
Q

Describe NCl3

A
  1. Less polarisation –> more reactive

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

19
Q

Describe NBr3/NI3

A
  1. More reactive

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

20
Q

Describe PF3

A
  1. Gas
  2. Hydrolysed slowly in H2O, Faster in alkali
  3. PF3 + 3OH- –> H3PO3 + 3F-
  4. Binds to haemoglobin- toxic
21
Q

Describe PCl3 reaction with water

A
  1. PCl3 + H2O –> H3PO3 + 3HCl
22
Q

Compare reaction of PCl3 and NCl3 with water

A
  1. P-Cl more polarised - OH2 attacks P

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

23
Q

Describe NF5

A
  1. Not known

2. N cannot achieve +5 oxidation state with halides

24
Q

Describe PF5

A
  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
25
Q

Describe AsF5

A
  1. Similar PF5
26
Q

Describe SbF5

A
  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
  5. Extended structures- atomic size
  6. Catenation- ring/chain formation
27
Q

Describe SbF5 use as superacids

A
  1. SbF5 can accept X- leading to their use in super acids

2. SbF5 + 2HSO3F (fluorosulfonic acid) –> ‘SbF6’

28
Q

What can superacids do

A
  1. Protonate methane

2. CH4 + H+ –>CH5+ –> H2 + CH3+ + 3CH4 –> C(CH3)3 + 3H2

29
Q

Describe bp of NH3

A
  1. Hydrogen bonds raises the bp
30
Q

Describe structure of BiF5

A
  1. Linear chains with trans-bridges

2. Too big to form a ring

31
Q

Describe PH3–> Bih3

A
  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
32
Q

Compare PH5 to PF5

A
  1. PH5 –> PH3 + H2 -exothermic due to strong H-H bond

2. PF5 –> PF3 + F2 - weak due to e–e- repulsion- does not happen

33
Q

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

A
  1. Incompatible overlap of E and H orbitals

2. Decreasing bond strength leads to increasing acidity - easier release of H+

34
Q

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

A
  1. Long bonds as there is less e- - e- repulsion compared to NH3
35
Q

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

A
  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
36
Q

Compare PH3 and NH3 reactions to protons

A
  1. PH3- more likely to release H+

2. NH3- more likely to abstract H+

37
Q

Describe allotropy and catenation of nitrogen

A
  1. N=- N - triple bond

2. Covalent gas

38
Q

Describe allotropy and catenation of phosphorus

A
  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
39
Q

Describe allotropy and catenation of As, Sb, Bi

A
  1. Adopt hexagonal sheet structures similar to black phosphorus
40
Q

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

A
  1. Covalent to metallic down the group

CH10134 (15 decks)

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