The document summarizes the acid-base properties of period 3 oxides and their reactions. Sodium and magnesium oxides are basic and will neutralize acids to form salts and water. Aluminum oxide is amphoteric and can react with both acids and bases. Silicon, phosphorus, and sulfur oxides are acidic and will neutralize bases to form salts and water. There is a transition from basic to acidic character going across the period, reflecting the transition from metallic to non-metallic character.

1. Regularity of changes in acid-base properties
of compounds in periods and groups
Learning Objectives:
10.2.1.4 explain the regularties of changes in the acid-base
properties of oxides, hydroxides and hydrogen compounds of
chemical elements by periods and groups

2. Which properties of the alkali metals decrease going
down group 1?
A. First ionization energy and reactivity
B. Melting point and atomic radius
C. Reactivity and electronegativity
D. First ionization energy and melting point
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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 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 P4O10 + 6 H2O  4 H3PO4 Strongly acidic
Sulphur* SO2
SO3
Molecular Covalent
SO3 + H2O  H2SO4
Strongly acidic
Chlorine no direct
reaction
but:
Cl2O7
Molecular Covalent
Cl2O7 + H2O  2 HClO4
Strongly acidic
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. OXIDES WITH ACIDS & BASES
pH OF PERIOD 3 OXIDES:
Na2O
MgO
Al2O3
SiO2
P4O10
SO2
SO3

5. 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. 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)
BASIC OXIDES
Create 2 other equations for
Na & Mg with different acids

7. 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)
AMPHOTERIC OXIDES

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. 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)
ACIDIC OXIDES

10. PRACTICE QUESTION
Q1 Why is Na more reactive than Mg with water?
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Q2 What type of bonding is in the following oxides: a) Na2O b) P2O5
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Q3 Write an equation for the reaction of Na2O wth water.
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Q4 Explain why MgO forms a less alkaline solution than Na2O
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