Topic 3 - chemical reactions period 2&3

Question 1

Reactions with Oxygen​

Answer 1

The reactions of metals with oxygen can influence how they are used​

E.g. Iron reacts with oxygen to form rust so is often painted to protect it from air​

The general pattern from left to right for the oxides formed by period 2 and 3 elements is:​
Ionic → giant covalent → small covalent​
Solids → gases​
Alkaline → amphoteric → acidic​

Question 2

Group 1 -Lithium

Answer 2

Rapid reaction, burns with a red flame​

Stored in oil to prevent reaction in air​

Metal oxide produced which forms an alkaline solution in water​
​
4Li(s) + O2(g) → 2Li2O(s)​
​
Oxide contains simple O2- ion

Question 3

Group 1 - Sodium​

Answer 3

Very vigorous reaction, burns with orange flame​

Stored in oil to prevent reaction in air​

Metal oxide produced which forms a basic solution in water​
​
4Na(s) + O2(g) → 2Na2O(s)​
2Na(s) + O2(g) → Na2O2(s)​
​
Oxide can contain simple O2- ion or the peroxide ion O22-

Question 4

Peroxides

Answer 4

The complicated molecular ion (O22- ) is unstable near small positive ions​

The covalent bond between the two negative oxygen ions is weak​

The electrons in the ions will be attracted to a positive ion BUT the positive ion can polarise the negative ion​

Lithium only has a 1+ charge but is small so has a high charge density. This causes the peroxide ion to break down to an oxide ion and an oxygen atom​
Therefore Lithium does not form a peroxide​

Sodium is a larger ion so the O22- ion can stay stable enough to form sodium peroxide

Question 5

Other group 1 metals

Answer 5

Potassium can form a peroxide in a similar way to sodium​

2K(s) + O2(g) → K2O2(s)​

Potassium, rubidium and caesium can also ignite in air to form super-oxides, KO2, RbO2 and CsO2​

These super-oxides contain the molecular ion O22- ​

The super-oxide ions are highly unstable and only remain stable in the presence of the larger, non-polarising ions at the bottom of group 1

Question 6

Group 2 - Beryllium​

Answer 6

Needs heat to react in similar way to group 1​
Very vigorous reaction​
​
2Be(s) + O2(g) → 2BeO(s)​
​
Forms a coating of beryllium oxide which prevents further oxidation​
Oxide is basic in nature

Question 7

Group 2 - Magnesium

Answer 7

Needs heat to react in similar way to group 1​

Very vigorous reaction​
​
2Mg(s) + O2(g) → 2MgO(s)​
​
Oxide is a base

Question 8

Other group 2 metals

Answer 8

Strontium and Barium will also form peroxides​

The general equation is:​
​
M + O2 → MO2

Question 9

Transition metals and oxygen

Answer 9

When transition metals (d-block) react with oxygen, the oxides formed are often brittle​

Iron oxide is rust​

Some d-block metals are resistant to corrosion because they form an unreactive oxide layer which protects the metal from further reaction (e.g. Titanium)​

D-block metals form a range of oxides​

D-block metals are much less reactive than group 1 and 2 in general

Question 10

Group 3 - Boron​

Answer 10

Burns with a brilliant flame to produce boron trioxide​
​
4B(s) + 3O2(g) → 2B2O3(s)​
​
Boron trioxide forms a thin film on the surface that prevents further reaction with oxygen​

Boron is the only element in group 3 which is NOT a metal

Question 11

Group 3 – Aluminium​

Answer 11

Vigorous reaction at first​
​
4Al(s) + 3O2(g) → 2Al2O3(s)​
​
forms a water-insoluble layer on the surface that prevents further reaction with oxygen​
​
Aluminium oxide is amphoteric

Question 12

Other group 3 metals

Answer 12

Thallium will react to produce Tl2O

Question 13

Group 4 - Carbon

Answer 13

Needs heat to react​
Forms slightly acidic oxides​
​
C(s) + O2(g) → CO2(g) complete combustion​

2C(g) + O2(g) → 2CO(g) incomplete combustion​

Question 14

Group 4 - Silicon​

Answer 14

Forms a thin layer of oxide which protects the rest so very little reaction​
​
Si(s) + O2(g) → SiO2(s)​
​
Silicon dioxide is slightly acidic

Question 15

Other group 4 elements​

Answer 15

Group 4 metals Lead and Tin can produce oxides with the formulae MO and MO2

Question 16

Group 5 - Nitrogen​

Answer 16

Forms a range of oxides with different oxidation states
​
High temperatures are needed for these reactions​
​
Can produce NO, NO2 and N2O5

Question 17

Group 5 - Phosphorus​

Answer 17

Burns vigorously with a white flame​
​
Forms P4O6 in limited oxygen​

Forms P4O10 in excess oxygen

Question 18

Group 6 - Oxygen​

Answer 18

Reaction can take place in the ozone layer​

O2 and O3 are allotropes (different physical forms of the same element)​
​
O(g) + O2(g) → O3(g)​

Question 19

Group 6 - Sulfur​

Answer 19

Burns slowly with a blue flame​

Two oxides form​
​
S(g) + O2(g) → SO2(g)​
2SO2 (g) + O2(g) → 2SO3(g)​

Question 20

Group 7 - Halogens​

Answer 20

Most halogens will form unstable oxides​

Not usually by direct reaction

Question 21

Group 0 – noble gases​

Answer 21

No reaction