Module 1 Inorganic Chemistry

Period 3 Elements

Ung Hie Huong

2

LEARNING OUTCOMES:

Students should be able to:

Describe the reactions of Period 3 elements with oxygen

Interpret the ability of elements to act as oxidising and reducing agents

Describe the reactions of Period 3 elements with water

Describe and explain the acid-base properties of oxides of Period 3 elements

1.1 Introduction to Period 3 elements

Group 1 2 13 14 15 16 17 18

Element Na Mg Al Si P S Cl Ar

Atomic radius Decreases

Entalphy of fusion Decreases

Entalphy of

vaporisation Decreases

First ionisation

energy Increases

Electronegativity Increases

Type of element Metal Metalloid Nonmetal

Electrical

conductivity Conductor

Semi

conductor Nonconductor

Type of bond Metallic bond Covalent bond

Physical state of

element at r.t.p. Solid Gas

Atomic radius (coded by ball size)

3

1.2 Reaction of Period 3 elements with oxygen

Group 1 2 13 14 15 16 17 18

Element Na Mg Al Si P S Cl Ar

+ O2 √

Na2O

√

MgO

√

Al2O3

√

SiO2

√

P4O6/ P4O10

(In excess O2)

√

X

X

Element Reaction with oxygen (Observation/ Equation)

Sodium, Na Observation Burns in oxygen with a bright yellow flame.

A white ionic solid, sodium oxide (Na2O) is formed.

Equation 4Na(s) + O2(g) 2Na2O(s)

White

Magnesium,

Mg

Observation Burns in oxygen with a brilliant white flame.

A white ionic solid, magnesium oxide (MgO) is formed.

Equation 2Mg(s) + O2(g) 2MgO(s)

White

Aluminium,

Al

Observation Burns in oxygen with a brilliant white flame.

A white ionic solid, aluminium oxide (Al2O3) is formed.

Equation 4Al(s) + 3O2(g) 2Al2O3(s)

White

Silicon, Si Observation Reacts slowly with oxygen.

White solid, silicon dioxide (SiO2) is formed.

Note: Silicon dioxide or silicon(IV) oxide has a giant

covalent structure.

Equation Si(s) + O2(g) SiO2(s)

White

Phosphorus,

P

Observation White phosphorus bursts into flames spontaneously when

exposed to air.

In limited amount of air: Phosphorus trioxide, P4O6, is

formed.

In excess air: Phosphorus pentoxide, P4O10, is formed.

Equation In limited amount of air: P4(s) + 3O2(g) P4O6(s)

In excess air: P4(s) + 5O2(g) P4O10(s)

Sulphur, S Observation Sulphur burns with a blue flame.

Sulphur dioxide, SO2 (colourless gas) is formed.

Sulphur dioxide, SO2 can be oxidised slowly to sulphur

trioxide, SO3.

Equation S(s) + O2(g) SO2(g)

2SO2(g) + O2(g) 2SO3(g)

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1.3 Reaction of Period 3 elements with water

Group 1 2 13 14 15 16 17 18

Element Na Mg Al Si P S Cl Ar

+ H2O √

NaOH

√

MgO

X X X X √

HCl + HOCl

X

Element Reaction with water (Observation/ Equation)

Sodium, Na Observation Reacts vigorously with water.

Forms an alkaline solution (turns pink litmus solution to

blue) & hydrogen gas (gives a ‘pop’ sound with burning

splinter)

Equation 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)

Alkali

Magnesium,

Mg

Observation Does not react with water.

React with steam.

Forms magnesium oxide (MgO) and hydrogen gas.

Equation Mg(s) + H2O(g) MgO(s) + H2(g)

Chlorine,

Cl2

Observation Reacts slowly with water.

Forms acidic solution, hydrochloric acid and chloric(I) acid.

Blue litmus solution turns red, then bleached/ decolourised.

Equation Cl2(g) + H2O(l) HCl(aq) + HOCl(aq)

Bleaching agent

ALL noble gases (Group 18 elements) are inert

and unreactive.

This is due to their duplet and octet valence

electron configuration.

The valence orbitals are all fully filled &

stable.

1.4 Acid-base properties of oxides of the Period 3 elements

Group 1 2 13 14 15 16 17

Oxide Na2O MgO Al2O3 SiO2 P4O6

P4O10

SO2

SO3

Cl2O

Cl2O7

Oxidation number +1 +2 +3 +4 +3

+5

+4

+6

+1

+7

Structure Ionic Ionic-covalent Giant covalent Simple covalent

Physical state (r.t.p.) Solid

Liquid

Solid

Gas

Gas

Gas

Liquid

Acid-base property Basic Weakly Basic Amphoteric Acidic Acidic Acidic Acidic

+ Water Dissolves

Na2O + H2O

2NaOH

Insoluble

The lattice energy that hold Mg

2+ ions

and O2–

ions together is too high

Insoluble Insoluble Dissolves

P4O6 + 6H2O

4H3PO3

P4O10 + 6H2O

4H3PO4

Dissolves

SO2 + H2O

H2SO3

SO3 + H2O

H2SO4

Dissolves

Cl2O + H2O

2HClO

Cl2O7 + H2O

2HClO4

+ HCl Dissolves

Na2O + 2HCl

2NaCl + H2O

Dissolves

MgO + 2HCl

MgCl2 + H2O

Dissolves

Al2O3 + 6HCl

2AlCl3 + 3H2O

- - - -

+ NaOH

- -

Dissolves

Al2O3 + 2NaOH

+ 3H2O

2NaAl(OH)4 Sodium aluminate

Dissolves in

conc. NaOH

SiO2 + 2NaOH

Na2SiO3 +

H2O

- - -

Electric conductivity Electrolyte (in molten & aqueous state) Non-electrolyte

Why is aluminium oxide amphoteric?

Because it is an ionic compound with partial covalent character.