Izod L4-6

Question 1

Describe group 13

Answer 1

Ground state electron configuration ns2np1

Question 2

What are the common oxidation states for group 13 metals

Answer 2

+1 and +3

Question 3

When is the +3 oxidation states for for group 13 observed

Answer 3

+3 observed for all group 13

Question 4

When is the +1 oxidation states for the group 13 observed

Answer 4

+1 observed for In, Tl
Lower oxidation state favoured for heavier elements

Question 5

Why is the +1 oxidation states for group 13 due to

Answer 5

The inert lone pair effect

Question 6

Describe bonding for boron

Answer 6

Valence electrons of boron experience high effective nuclear charge. Therefore the bonding is covalent

Question 7

Describe the trihalides for boron. Are these all know? What is there properties?

Answer 7

BX3 known for all X: BF3 colourless gas, BCl3/BBr3 colourless liquid, BI3 colourless solid

Question 8

Why are boron trihalides good Lewis acids

Answer 8

In BX3 Boron has only 6 electrons in its valence shell in these molecules.
It has an empty 2p orbital making it electron deficient (Lewis acid) and can accept a lone pair from a Lewis base. Therefore, BX₃ compounds can form adducts with electron-pair donors.

Question 9

Describe the order of trihalides in terms of Lewis acidity

Answer 9

BBr3>BCl3>BF3

Question 10

Describe the bonding in BX3

Answer 10

Boron forms 3 sigma bonds with all 3 halogens, and because the halogens can donate some electrons from the lone pair into the vacant 2p orbital on boron there is a pi orbital across all 4 atoms. So 3 sigma and 1 pi orbital so B-X bond order is 1 and 1/3

Question 11

What happens when BF3 reacts with a Lewis base

Answer 11

BF3 reacts with Lewis bases to give adducts. During reaction lone pair attacks lumo (pi) populates pi. Breaks pi interaction forming new sigma bonds.

Question 12

Why is BF3 a poorer Lewis acid

Answer 12

Strongest more stable pi-bond formed in BF3. Lower energy homo (pi), higher energy lumo (pi*) due to good pi overlap therefore poorer Lewis acid

Question 13

Why is BBr3 a stronger Lewis acid

Answer 13

Poor B-Br pi overlap. Higher energy homo (pi), lower energy lumo (pi). Pi is more accessible therefore stronger Lewis acid.

Question 14

What is B(OH)3

Answer 14

Boric acid

Question 15

Describe the shape and reactivity of B(OH)3

Answer 15

B(OH)3 planar with delocalised pi-orbital across BO3 core.
B(OH)3 Lewis acidic electron deficient has empty p orbital.
Also B3+ is very polarising as it so withdraw electron density and therefore is a bronsted acid .

Question 16

Describe the structure of B(OH)3

Answer 16

Since O-H polar -> O-H - - - - O hydrogen bonding. B(OH)3 solid with sheet structure

Question 17

Describe the reaction when B(OH)3 with OH- and how it acts as a Lewis acid

Answer 17

B(OH)3 + OH- -> [B(OH)4]-

Question 18

Describe the boron hydrides BH3

Answer 18

BH3 actually B2H6. Dimerises through donation of B-H electron density into vacant p orbital on adjacent B.

Question 19

Describe B2H6

Answer 19

B2H6 is Lewis acid and forms adducts
For example B2H6 can react with 2Me3N to form adducts

Question 20

Which group 13 element is the most electropositive

Answer 20

Aluminium

Question 21

why is aluminium the most electropositive element in group 13

Answer 21

Aluminium is the most electropositive Group 13 element due to 3d/lanthanide contractions. It readily forms Al³⁺, has low ionization energy, high metallic character, and isn’t affected by the inert pair effect like its heavier groupmates. more ionic character in bonds

Question 22

Describe aqueous solutions of aluminium and write the reaction

Answer 22

Aqueous solutions of aluminium are acidic.
[Al(OH2)6]+3 + H2O -> [Al(OH2)5(OH)]+2 + H3O+
Very polarising Al +3 centre
Diagonal relationship between Be and Al

Question 23

Describe the group 13 trifluorides

Answer 23

MF3 poorly soluble high m.p network materials

Question 24

Describe the group 13 trichlorides and tribromides

Answer 24

MCl3/MBr3 dimeric molecules

Question 25

Describe the group 13 trihalides

Answer 25

All MX3 are Lewis acidic and forms aducts MX3 + LiCl -> Li^+[MX4]-

Question 26

Describe the group 13 triiodides

Answer 26

AlI3, GaI3, InI3 similar but TlI3 is actually Tl^I(I3)- due to inert lone pair effect

Question 27

What is alane

Answer 27

AlH3

Question 28

Describe the chemistry of alane/AlH3

Answer 28

High melting point solid Reacts with H2O very vigorously Readily forms aducts, the adducts is a very useful hydride transfer reagent AlH3 + LiH -> Li^+[AlH4]-

Question 29

Write the reaction with AlH3 and H2O

Answer 29

AlH3 + 3H2O -> Al(OH)3 + 3H2 Very vigorous

Question 30

Describe GaH3

Answer 30

Thermally unstable liquid

Question 31

Describe InH3/TlH3

Answer 31

Cannot be isolate

Question 32

Electron configurations group 14 elements

Answer 32

Ground state electronic configuration ns2np2.

Question 33

Describe the common oxidation states for group 14 elements

Answer 33

+4 all element less favoured for Pb +2 for heavier elements especially Sn and Pb - due to inert lone pair effect

Question 34

Compare the reactivity of CCl4 and SiCl4 with water

Answer 34

CCl4 is immiscible with H2O SiCl4 highly reactive towards H2O

Question 35

Write the reaction when CCl4 reacts with H2O

Answer 35

CCl4 + 2H2O -> CO2 + 4HCl But reactions do not proceed

Question 36

Write the reactions when SiCl4 react with H2O

Answer 36

SiCl4 + 2H2O -> SiO2 + 4HCl Very vigorous instantaneous reactions

Question 37

Why does CCl4 not react with water

Answer 37

In CCl4 C uses all 4 valence orbital (2s/2p) to form 4 sigma bonds. There is good C-Cl orbital overlap. Low energy homo (σ), high energy lumo σ*

Question 38

Why does SiCl4 react vigorously with water

Answer 38

In SiCl4 Si uses all 4 valence orbital (3s/3p) to form 4 sigma bonds. But the silicon valence orbital large/diffuse. Si-Cl orbitals overlap poor. High energy homo σ, low energy lumo σ*. Low lying Si-Cl σ* orbitals are susceptible to attack by nucleophile therefore rapid hydrolysis. C-Cl σ* orbitals to high in energy so not energetically accessible

Question 39

How is a Si-X stronger than C-X but Si-X σ overlap poorer than C-X σ overlap?

Answer 39

Si valence orbitals are large/diffuse, poor Si-X σ overlap, low energy σ*. Lone pair on X overlaps with Si-X σ*. Therefore hyperconjugation with Si-X stronger than just σ bond. There is no hyperconjugation for C-X as the σ* too high in energy for good overlap with X lone pair. C-X purely σ bonding

Question 40

What does the effect of hyperconjugation decrease with

Answer 40

Effect of hyperconjugation decreases with increasing atomic number of X so the difference between C-X and Si-X descreases

Question 41

When else is this hyperconjugation seen for

Answer 41

hyperconjugation also seen for Si-O vs C-O and in Si-N vs C-N

Question 42

How can we produce organisilicon halides

Answer 42

Reacting SiCl4 with RMgX SiCl4 + 2RMgX -> R2SiCl2 + 2MgXCl Or the Dow process 2MeCl + Si -> Me2SiCl2 + Me3SiCl + MeSiCl3

Question 43

describe the properties of Si halides

Answer 43

si halides readily hydrolyse and form polymers