Group 13 Flashcards
What is the maximum oxidation state of group 13 elements
- +3
Describe the major properties of group 13 halides
- Lewis acids- AX3
- Empty p-orbitals so are electron poor
- They have 6 valence electrons so accept electrons from lewis base to achieve a stable octet
Describe BX3
- Monomeric
- Trigonal planar
- More volatile than Al analogue
What happens to the B-X bond length F–>I
- Increases
Describe the states of BX3 and why
- BF3, BCl3= gas
- BBr3= liquid
- BI3= solid
- As increasing molecular weight so increase in Van der Waals forces
How can BF3 be synthesised and give equation
- B2O3 + 3CaF2 + 3H2SO4 –> 2BF3 + 3CaSO4 + 3H2O
2. Boron trioxide
What happens once BF3 is formed
- Excess H2O leads to hydrolysis of BF3
- 4BF3 + 6H2O –> 3[H3O]+ + 3[BF4]- + B(OH)3 (Boric acid)
- 3[H3O]+ + 3[BF4]- –> 3HBF4 + 3H2O
Describe properties of HBF4
- Non-insoluble strong acid
2. commercially available as an Et2O (ether) solution
How can HBF4 be synthesised deliberately
- B(OH)3 + 4HF –> H3O+ + BF4- + 2H2O
2. H3O+ + BF4- –> HBF4 strong acid
Describe BF4-
- Encountered in coordination chemistry
- Weakly coordinating compared to strong acid
- Used to precipitate cation
- Innocent- anion doesn’t attach to coordination centre, always has the free centre for chemistry
- [M+] [BF4-] stabilise each other but don’t react
How can you form BF3 complexes
- Using ethers e.g. ET2O
2. SP2 hybridised –> sp3 hybridised - the oxygen lone pair donates into empty p-orbital
What adducts do BF3 form
- BX3.L
- X= Halide
- L= lewis base/donor group e.g. Et2O, THF, NR3
Which of the BX3.L are most stable
- L.BF3
Describe the trent in BX3.L stability
- Opposite trend than expected based on halide electronegativity
- Would expect F to withdraw e- density render B delta +, therefore more prone to attack by L
- BUT B-X bonds have partial pi character
- When L coordinates the charge to sp3 the pi interactions are lost- endothermic reorganisation
- L-B bond formation is exothermic- dative bond
- F is strongest stabiliser –> smaller size –> better overlap
- Therefore there is a bigger energy deficit on loss of B-F pi bond character
- Better B-F overlap, stronger bond, more pi character
Describe halides of Al, Ga, ln, Tl
- Unlike boron halide, they tend to form dimers, oligomers, infinite networks
Describe AlF3
- Has octahedral structure with 6 f atoms each linked to 2 Als
How is AlF3 prepared
- Al2O3 + 6HF –> 2AlF3 + 3H2O
2. React oxide with HF
How can the infinite structure of AlF3 be broken
- Forming an anion
2. [Al2F10]-[pyH]4+
Describe MX3 Al, Ga, In with Cl, Br, I
- Dimeric in solution
- Formed from the elements
- 3 centre 4 electron bonding
Describe what happens when water is added to AlCl3
- AlCl3 + 6H2O –> [Al(H2O)6]3+3Cl-
- Hydrolysis
- In coordinating solvents adducts form AlCl3.H2O
- Used to split up the dimer
Describe boron oxide
- B(OH)3 is acidic
- Not just because of loss of H+
- B(OH)3 + H2O B(OH)3OH2 B(OH)4 - + H+
- sp2 –> sp3
How is B(OH)3 formed
- Hydrolysis of B2O3
- Na2B4O7 + H2SO4–> B2O3 + 3H2O + Na2SO4
- B2O3 + 3H2O–> 2B(OH)3
- Heat
How is alumina formed
- Heating Al(OH)3
2. Al(OH)3 –> Al2O3 + 3H2O
What is the most common soluble salt of Al
- Aluminium sulfate octadecahydrate Al2(SO4)3.18H2O
- It is acidic in aqueous solutions
- Forms a strong hydration complex with water Al(H2O)6 3+ - Source of acidity
- This in turn hydrolyses
Show equations for hydrolysis of alumina from Al(H2O)6 3+
- Al(H2O)6 3+ + H2O [Al(H2O)5OH]2+ + H3O+
- Hydrolysis can continue until Aluminium hydroxide forms
- [Al(H2O)5OH]2+ + H2O [Al(H2O)4(OH)2]+ + H3O+
- [Al(H2O)4OH2]+ + H2O [Al(H2O)3(OH)4]+ + H3O+
- [Al(H2O)3(OH)4]+ = Al(OH)3.3H2O white precipitate
Describe aluminium hydroxide
- Amphoteric- acts as acid and base
2. Amphoteric nature is reflection of the partial non-metal character of aluminium
Describe what happens when aluminium hydroxide reacts with acids
- Acts as a base- neutralisation reaction
2. Al(OH)3 + 3H3O+ –> Al3+ + 6H2O
Describe what happens when aluminium hydroxide reacts with a base
- A hydroxo ion forms (an aluminate ion)
- The acidic behaviour of the hydroxide is typical of a non-metal hydroxide
- Al(OH)3 + OH- –> Al(OH)4- = water soluble
Describe AlMe6
- It is volatile, reactive liquid- flammable in air
- Similar to AlCl3 but no lone pairs/filled orbitals to donate e- density into the Al empty p-orbital
- 3C-2e- bonding
Describe catenation of Boron
- Strong covalent B-B bonds
- B12 icosahedra linked in 3D network
- Second hardest element
Describe catenation of Al
- Forms metallic lattice
Describe catenation of Ga
- Forms strong Ga-Ga pairs
- Interact weakly with 6 other Ga atoms
- Van der Waals
- Not metallic lattices- covalent in character due to d-block contraction
Describe catenation of In and Tl
- Forms metallic lattice
