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CH10134 > Group 13 > Flashcards

Group 13 Flashcards

1
Q

What is the maximum oxidation state of group 13 elements

A
  1. +3
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2
Q

Describe the major properties of group 13 halides

A
  1. Lewis acids- AX3
  2. Empty p-orbitals so are electron poor
  3. They have 6 valence electrons so accept electrons from lewis base to achieve a stable octet
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3
Q

Describe BX3

A
  1. Monomeric
  2. Trigonal planar
  3. More volatile than Al analogue
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4
Q

What happens to the B-X bond length F–>I

A
  1. Increases
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5
Q

Describe the states of BX3 and why

A
  1. BF3, BCl3= gas
  2. BBr3= liquid
  3. BI3= solid
  4. As increasing molecular weight so increase in Van der Waals forces
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6
Q

How can BF3 be synthesised and give equation

A
  1. B2O3 + 3CaF2 + 3H2SO4 –> 2BF3 + 3CaSO4 + 3H2O

2. Boron trioxide

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7
Q

What happens once BF3 is formed

A
  1. Excess H2O leads to hydrolysis of BF3
  2. 4BF3 + 6H2O –> 3[H3O]+ + 3[BF4]- + B(OH)3 (Boric acid)
  3. 3[H3O]+ + 3[BF4]- –> 3HBF4 + 3H2O
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8
Q

Describe properties of HBF4

A
  1. Non-insoluble strong acid

2. commercially available as an Et2O (ether) solution

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9
Q

How can HBF4 be synthesised deliberately

A
  1. B(OH)3 + 4HF –> H3O+ + BF4- + 2H2O

2. H3O+ + BF4- –> HBF4 strong acid

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10
Q

Describe BF4-

A
  1. Encountered in coordination chemistry
  2. Weakly coordinating compared to strong acid
  3. Used to precipitate cation
  4. Innocent- anion doesn’t attach to coordination centre, always has the free centre for chemistry
  5. [M+] [BF4-] stabilise each other but don’t react
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11
Q

How can you form BF3 complexes

A
  1. Using ethers e.g. ET2O

2. SP2 hybridised –> sp3 hybridised - the oxygen lone pair donates into empty p-orbital

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12
Q

What adducts do BF3 form

A
  1. BX3.L
  2. X= Halide
  3. L= lewis base/donor group e.g. Et2O, THF, NR3
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13
Q

Which of the BX3.L are most stable

A
  1. L.BF3
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14
Q

Describe the trent in BX3.L stability

A
  1. Opposite trend than expected based on halide electronegativity
  2. Would expect F to withdraw e- density render B delta +, therefore more prone to attack by L
  3. BUT B-X bonds have partial pi character
  4. When L coordinates the charge to sp3 the pi interactions are lost- endothermic reorganisation
  5. L-B bond formation is exothermic- dative bond
  6. F is strongest stabiliser –> smaller size –> better overlap
  7. Therefore there is a bigger energy deficit on loss of B-F pi bond character
  8. Better B-F overlap, stronger bond, more pi character
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15
Q

Describe halides of Al, Ga, ln, Tl

A
  1. Unlike boron halide, they tend to form dimers, oligomers, infinite networks
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16
Q

Describe AlF3

A
  1. Has octahedral structure with 6 f atoms each linked to 2 Als
17
Q

How is AlF3 prepared

A
  1. Al2O3 + 6HF –> 2AlF3 + 3H2O

2. React oxide with HF

18
Q

How can the infinite structure of AlF3 be broken

A
  1. Forming an anion

2. [Al2F10]-[pyH]4+

19
Q

Describe MX3 Al, Ga, In with Cl, Br, I

A
  1. Dimeric in solution
  2. Formed from the elements
  3. 3 centre 4 electron bonding
20
Q

Describe what happens when water is added to AlCl3

A
  1. AlCl3 + 6H2O –> [Al(H2O)6]3+3Cl-
  2. Hydrolysis
  3. In coordinating solvents adducts form AlCl3.H2O
  4. Used to split up the dimer
21
Q

Describe boron oxide

A
  1. B(OH)3 is acidic
  2. Not just because of loss of H+
  3. B(OH)3 + H2O B(OH)3OH2 B(OH)4 - + H+
  4. sp2 –> sp3
22
Q

How is B(OH)3 formed

A
  1. Hydrolysis of B2O3
  2. Na2B4O7 + H2SO4–> B2O3 + 3H2O + Na2SO4
  3. B2O3 + 3H2O–> 2B(OH)3
  4. Heat
23
Q

How is alumina formed

A
  1. Heating Al(OH)3

2. Al(OH)3 –> Al2O3 + 3H2O

24
Q

What is the most common soluble salt of Al

A
  1. Aluminium sulfate octadecahydrate Al2(SO4)3.18H2O
  2. It is acidic in aqueous solutions
  3. Forms a strong hydration complex with water Al(H2O)6 3+ - Source of acidity
  4. This in turn hydrolyses
25
Q

Show equations for hydrolysis of alumina from Al(H2O)6 3+

A
  1. Al(H2O)6 3+ + H2O [Al(H2O)5OH]2+ + H3O+
  2. Hydrolysis can continue until Aluminium hydroxide forms
  3. [Al(H2O)5OH]2+ + H2O [Al(H2O)4(OH)2]+ + H3O+
  4. [Al(H2O)4OH2]+ + H2O [Al(H2O)3(OH)4]+ + H3O+
  5. [Al(H2O)3(OH)4]+ = Al(OH)3.3H2O white precipitate
26
Q

Describe aluminium hydroxide

A
  1. Amphoteric- acts as acid and base

2. Amphoteric nature is reflection of the partial non-metal character of aluminium

27
Q

Describe what happens when aluminium hydroxide reacts with acids

A
  1. Acts as a base- neutralisation reaction

2. Al(OH)3 + 3H3O+ –> Al3+ + 6H2O

28
Q

Describe what happens when aluminium hydroxide reacts with a base

A
  1. A hydroxo ion forms (an aluminate ion)
  2. The acidic behaviour of the hydroxide is typical of a non-metal hydroxide
  3. Al(OH)3 + OH- –> Al(OH)4- = water soluble
29
Q

Describe AlMe6

A
  1. It is volatile, reactive liquid- flammable in air
  2. Similar to AlCl3 but no lone pairs/filled orbitals to donate e- density into the Al empty p-orbital
  3. 3C-2e- bonding
30
Q

Describe catenation of Boron

A
  1. Strong covalent B-B bonds
  2. B12 icosahedra linked in 3D network
  3. Second hardest element
31
Q

Describe catenation of Al

A
  1. Forms metallic lattice
32
Q

Describe catenation of Ga

A
  1. Forms strong Ga-Ga pairs
  2. Interact weakly with 6 other Ga atoms
  3. Van der Waals
  4. Not metallic lattices- covalent in character due to d-block contraction
33
Q

Describe catenation of In and Tl

A
  1. Forms metallic lattice

CH10134 (15 decks)

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