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
Refresh
Which properties of the alkali metals decrease
going down group 1?
A.
B.
C.
D.
First ionization energy and reactivity
Melting point and atomic radius
Reactivity and electronegativity
First ionization energy and melting point
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
Giant Ionic
Slight: MgO + H2O 
Mg(OH)2
Weakly basic
Aluminium
Al2O3
Giant Ionic
Amphoteric
Silicon
SiO2
Giant Covalent
(Metalloid)
Very weakly
acidic
Phosphorous*
P4O10
Molecular Covalent
Sulphur*
SO2
SO3
Molecular Covalent
no direct
reaction
but:
Cl2O7
Molecular Covalent
Chlorine
Argon
P4O10 + 6 H2O  4 H3PO4
Strongly acidic
Strongly acidic
SO3 + H2O  H2SO4
Strongly acidic
Cl2O7 + H2O  2 HClO4
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, *
13.3 OXIDES WITH ACIDS & BASES
pH OF PERIOD 3 OXIDES:
P4O10
SO3
SO2
MgO
SiO2
Al2O3
Na2O
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
BASIC OXIDES
SODIUM & MAGNESIUM:
Create 2 other equations for
Na & Mg with different acids
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)
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)
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:
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)
Complete Test Yourself Questions
• Page 103
• Questions 6 – 8
• Check your answers on page 559