All the elements in Group IV form tetrachlorides, XCI4
Tetrachlorides
Simple covalent molecules with tetrahedral structure
Volatile liquids with low boiling points
Non-polar because the dipoles cancel
There is no simple pattern in the boiling points of the tetrachlorides
Group IV tetrachlorides
Compounds formed by Group IV elements (C, Si, Ge, Sn, Pb) with four halogen atoms
Reactivity of the Group IV tetrachlorides with water
1. All the tetrahalides, except CCl4, are readily hydrolysed by water to the oxide in the +4 oxidation state
2. Acidic fumes of hydrogen chloride are also produced
Hydrolysis reaction of tetrachlorides
SiCl4(l) + 2H2O(l) → SiO2(s) + 4HCl(g)
GeCl4(l) + 2H2O(l) ⇌ GeO2(s) + 4HCl(g)
Hydrolysis of the Group IV tetrachlorides
The hydrolysis is reversible for the heavier tetrachlorides
The case of hydrolysis increases down the group from SiCl4 to PbCl4 as the metallic nature of the Group IV atom increases
When lead(IV) chloride is hydrolysed, a little decomposition of the lead(IV) chloride to lead(II) chloride also occurs
Group IV elements
C, Si and Ge have giant covalent structures; Sn and Pb are metals
Down Group IV, the elements show a general decrease in melting point and a general increase in metallic character and electrical conductivity
Group IV elements form covalently bonded tetrachlorides
The Group IV tetrachlorides are hydrolysed rapidly by water with the exception of carbon tetrachloride
Oxides, apart from CO and CO2
Solids with giant structures and high melting points
CO and CO2
Gases at room temperature, because they have a simple molecular structure with only weak forces between their molecules in the solid and liquid states
Carbon monoxide, CO
Has a strong triple bond and does not decompose on heating
Germanium(II) oxide disproportionation
2GeO(s) → GeO2(s) + Ge(s)
Oxidation numbers of Germanium(II) oxide: +2, +4, 0
Tin(II) oxide, SnO, and lead(II) oxide, PbO
Do not decompose on heating in the absence of air, readily oxidised to higher oxides in the presence of oxygen
Carbon dioxide, CO2
Has strong double bonds and does not decompose on heating
The oxides in the +4 oxidation state
Tend to decrease in stability down the group, except lead(IV) oxide, PbO2, which undergoes significant thermal decomposition
Thermal decomposition of lead(IV) oxide
PbO2(s) → PbO(s) + O(g)
Acid-base properties of oxides
CO - very weakly acidic
CO2 - acidic
SiO - very weakly acidic
SiO2 - amphoteric
GeO - amphoteric
GeO2 - amphoteric
SnO - amphoteric
SnO2 - amphoteric
PbO - amphoteric
PbO2 - amphoteric
The oxides in the +2 oxidation state
Are less acidic (more basic) than the corresponding oxides in the +4 oxidation state
CO2 reaction with water
CO2(g) + H2O →<— HCO3(aq) + H+(aq)
CO2 reaction with dilute alkalis
CO2(g) + 2NaOH(aq) → Na2CO3(aq) + H2O
The oxides in both oxidation states
Become more basic down the group as the metallic character of the Group IV atom increases
Reactions of carbon dioxide and silicon dioxide with alkalis
CO2 reacts with aqueous alkalis (hydroxide ions)
SiO2 only reacts with hot concentrated alkali
SiO2 reaction with hot concentrated alkali
SiO2(s) + 2NaOH(aq) → Na2SiO3(aq) + H2O
Amphoteric oxides of Group IV
GeO2, SnO and PbO are all amphoteric, but have increasingly basic character in the order GeO2 < SnO < PbO
They all react with acids to form a salt with oxidation state +2
They all react with alkalis to form ions with oxidation state +2
Amphoteric oxides of Group IV (oxidation state +2) reaction with acids
SnO(s) + 2HCl(aq) → SnCl2(aq) + H2O
Amphoteric oxides of Group IV (oxidation state +2) reaction with alkalis
1. GeO(s) + 2OH-(aq) → GeO2-(aq) + H2O
2. SnO(s) + 2OH-(aq) → SnO2-(aq) + H2O
3. PbO(s) + 2OH-(aq) → PbO2-(aq) + H2O
Amphoteric oxides of Group IV (oxidation state +4)
GeO2, SnO2 and PbO2 are all amphoteric
They all react with acids to form a salt with oxidation state +4
They all react with alkalis to form ions with oxidation state +4
Amphoteric oxides of Group IV (oxidation state +4) reaction with acids
SnO2(s) + 4HCl(aq) → SnCl4(aq) + 2H2O
The relative stability of Group IV oxides in oxidation state +4
Decreases down the group
The acidic character of the Group IV oxides in oxidation state +2 and +4
Decreases down the group and the basic character increases
Group IV oxides in oxidation state +2 are more basic than the corresponding oxides in oxidation state +4
Carbon monoxide
This gas is prepared in the laboratory by using warm concentrated sulphuric acid to dehydrate methanoic acid
Carbon monoxide
Burns with a pale blue flame
Forms carbon dioxide: 2CO(g) + O2(g) → 2CO2(g)
Carbon monoxide's most notorious characteristic
Ability to bind tightly to haemoglobin in the blood, preventing haemoglobin from carrying oxygen around the body
Carbon monoxide gas forms as the result of incomplete combustion in petrol engines, and also in poorly ventilated gas fires, causing preventable deaths
Oxide character
As a general rule, the metalloids are usually basic, although some can vary from non-metal to metal-like as the group is descended, becoming less acidic (i.e. more basic) as the atomic number increases
Carbon dioxide can dissolve in water to form a slightly acidic solution (pH=5)