1. Title: Lesson 4 Period 3 Oxides
Learning Objectives:
Understand and explain the trend in acid-base behaviour of the period 3 oxides
Complete an experiment to demonstrate the amphoteric nature of aluminium oxide

2. Refresh
Which properties of the alkali metals decrease going down group 1?
First ionization energy and reactivity
Melting point and atomic radius
Reactivity and electronegativity
First ionization energy and melting point

3. The Period 3 Oxides
Element
Formula of oxide
Structure
Reaction of oxide with water
Acid/base nature
Sodium*
Na2O
Giant Ionic
Na2O + H2O  2NaOH
Strongly basic
Magnesium*
MgO
Slight: MgO + H2O  Mg(OH)2
Weakly basic
Aluminium
Al2O3
Amphoteric
Silicon
SiO2
Giant Covalent (Metalloid)
Very weakly acidic
Phosphorous*
P4O10
Molecular Covalent
P4O H2O  4 H3PO4
Strongly acidic
Sulphur*
SO2
SO3
SO3 + H2O  H2SO4
Chlorine
no direct reaction but:
Cl2O7
Cl2O7 + H2O  2 HClO4
Argon
no oxides
There is a gradual transition from basic to acidic character, reflecting a gradual transition from metallic to non-metallic nature
Note: you will only be tested on the elements marked with an asterisk, *

4. 13.3 OXIDES WITH ACIDS & BASES
pH OF PERIOD 3 OXIDES:
P4O10
MgO
SO2
Al2O3
SO3
SiO2
Na2O

5. 13.3 OXIDES WITH ACIDS & BASES
A CLASSIC
The equation for neutralising an acid with a base is a classic
Acid + Base  Salt + Water
It’s no different for Period 3 oxides
You will be expected to write the equations

6. BASIC OXIDES SODIUM & MAGNESIUM:
Na2(s) + H2O(l)  2NaOH (aq) (Alkaline solution formed)
These oxides are basic so will neutralise acids.
E.g. Sodium oxide reacts with hydrochloric acid to form Sodium chloride and water
Na2O(s) + 2HCl(aq)  2NaCl(aq) + H2O(l)
E.g. Magnesium oxide reacts with sulphuric acid to form magnesium sulphate and water
MgO(s) + H2SO4(aq)  MgSO4(aq) + H2O(l)
Create 2 other equations for Na & Mg with different acids

7. AMPHOTERIC OXIDES ALUMINIUM OXIDE:
Aluminium Oxide does not affect pH when added to water because it is insoluble.
This is an amphoteric oxide  it can react with both acids and alkalis
E.g. With sulphuric acid, aluminium sulphate is formed
Al2O3(s) + 3H2SO4(aq)  Al2(SO4)3 (aq) + 3H2O(l)
Reaction with bases: Aluminum oxide also displays acidic properties, as shown in its reactions with bases such as sodium hydroxide. Various aluminates (compounds in which the aluminum is a component in a negative ion) exist, which is possible because aluminum can form covalent bonds with oxygen.
E.g. With hot, concentrated sodium hydroxide, sodium aluminate is formed
Al2O3(s) + 2NaOH(aq) + 3H2O(l)  2NaAl(OH)4(aq)

8. Acidic Oxides Non metallic oxides react with water to produce acidic
solutions:
Phosphorous(V) oxide reacts with water to produce:
Phosphorous (III) oxide reacts with water to produce:
Sulphur trioxide reacts with water to produce sulphuric(VI) acid:
Sulphur dioxide reacts with water to produce sulphuric(IV) acid:

9. ACIDIC OXIDES SILICON, PHOSPHOROUS & SULPHUR:
These oxides are all acidic so will neutralise bases
P4O10(s) + 12NaOH(aq)  4Na3PO4(aq) + 6H2O(l)
SO2(g) + 2NaOH(aq)  Na2SO3(aq) + H2O(l)
SO3(g) + 2NaOH(aq)  Na2SO4(aq) + H2O(l)
Lewis Acids  electron pair acceptors Lewis Bases  An electron pair donor

10. Complete Test Yourself Questions
Page 103
Questions 6 – 8
Check your answers on page 559