Group 14

Question 1

Name the group 14 elements

Answer 1

Carbon, silicon, germanium, tin, lead

Question 2

Which of the group 14 elements are non metals, metalloids and metals?

Answer 2

carbon - non metal
silicon - metalloid
germanium - metalloid
tin - metal
lead - metal

Question 3

Describe the diamond structure

Answer 3

• sp3 hybridisation
• 4 x sigma bonds
• extended covalent structure
• Si, Ge and Sn can also form a diamond structure

Question 4

Describe the graphite structure

Answer 4

• sp2 hybridisation
• sigma and pi bonding in plane
• weak interplanar attractions
• no silicon analogue bc the Si-Si p-pi p-pi bonds are too weak

Question 5

What is the buckyball?

Answer 5

An allotrope of carbon, C60, also known as buckminster fullerene, soluble in hydrocarbons, truncated icosahedron

Question 6

How is fullerene synthesised?

Answer 6

Electric discharge between two graphite electrodes in an inert atmosphere, this produces soot and fullerenes

Question 7

Describe the structure of graphene

Answer 7

single layer of graphite, 2010 Nobel prize, prepared by ‘exfoliation’ of graphite with scotch tape.

Question 8

List 2 uses of carbon

Answer 8

Graphite - lubricant
Diamond - industrial cutting tools
coal - reductant for metal extraction

Question 9

what are silicon, germanium, tin and lead used for?

Answer 9

silicon - semiconductor - electronics
germanium - semiconductor - electronics
tin - float glass process, alloyed w/ Cu - bronze
lead - radiation shields

Question 10

Why is SiX4 readily hydrolysed?

Answer 10

because of the polarity of its bonds

Question 11

Draw the reaction of 2 eqs of pyridine with GeCl4 and explain why the reaction happens

Answer 11

forms 6 coordinate adduct with the GeCl4, this is because GeCl4 is lewis acidic. The other MX4 molecules are lewis acidic too. (Ge, Sn, Pb)

Question 12

How does the stability of the oxidation state +2 change from Ge to Pb

Answer 12

The stability of the +2 oxidation state increases down the group. We can see this in the reaction PbCl4 –> PbCl2 + Cl2 at room temperature. Pb(IV) halides are unstable

Question 13

Which bonds are weaker C-C and C-H or Si-Si and Si-H?

Answer 13

The silicon bonds are weaker because silicon is a larger atom, so the orbital overlap is smaller

Question 14

Why are silanes highly reactive?

Answer 14

Because of their lewis acidity

Question 15

What is the general formula for silanes?

Answer 15

Si n H 2n+2

Question 16

Which of the following should be kept in anhydrous conditions and why? CX4, SiX4

Answer 16

SiX4 is susceptible to hydrolysis because it is lewis acidic/ Si can be hypervalent, should be kept in anhydrous conditions or it will form Si(OH)4. CX4 isn’t susceptible to hydrolysis, not lewis acidic

Question 17

Draw the bonding in carbon monoxide

Answer 17

triple bond one lone pair on each

Question 18

Describe the appearance, pH and reactivity of CO

Answer 18

It is a colourless, odourless gas. It is a Lewis acid because of the lone pair on each atom. It reacts well as a ligand for transition metals because of the C lone pair, therefore can also be used as a feedstock for chemical industry (can form complexes w/ TMs). It binds to haemoglobin 100x more strongly than oxygen.

Question 19

Describe the appearance, pH and reactivity of CO2

Answer 19

CO2 is a colourless odourless gas. No liquid phase at atmospheric pressure (67 atm it’s liquid). Solid is called cardice. Weak acid when dissolved in water. Used as a refrigerant, in fizzy drinks etc.

Question 20

How does the strength of the Si-O bond compare to the C-O bond?

Answer 20

Si-O stronger because of polarity

Question 21

How does the Si=O strength compare to the C=O strength?

Answer 21

The Si=O bond isn’t known because it doesn’t occur due the difference in p orbital size between Si and O. The C=O bond however is strong. Si form 4 single bonds to O while C form 2 double bonds.

Question 22

Describe the structure of CO2 compared to SiO2

Answer 22

CO2 is covalent and molecular

SiO2 is covalent and polymeric - it forms beta quartz and cristobalite which has a fcc structure

Question 23

Draw the orthosilicate anion and give two examples of how it condenses

Answer 23

[SiO4]4-

tries to condense to species with less charge on each atom. Pyrosilicate [Si2O7]6- . Cyclic metasilicate {[SiO3]2-}

Question 24

Name two uses of sheet silicate [Si2O5]2-

Answer 24

Talc and white asbestos

Question 25

What are zeolites and how are they formed?

Answer 25

Zeolites are a class of aluminosilicates. They are derived from SiO2 structure where some Si4+ is replaced with Al3+. This results in excess -ve charge which causes them to bind to cations.

Question 26

Explain three applications of zeolites

Answer 26

Ion exchange - water softening
Drying agent - H2O binds strongly into supercages, used for drying gases, solvents etc.
Size selective catalysis - Reactive surface within supercage (powerful Bronstead acid) only molecules smaller than 4.2A can fit pass through

Question 27

What are silicones? Give some applications

Answer 27

Also known as polysiloxanes, they are a polymer with a Si - O - Si -O backbone
-silicone elastomers, dimethicone - shampoos, conditioners etc., silly putty