AN INTRODUCTION TO PERIOD 3 COMPOUNDS A guide for A level students KNOCKHARDY PUBLISHING.

AN INTRODUCTION TOAN INTRODUCTION TO PERIOD PERIOD 3 COMPOUNDS3 COMPOUNDS

A guide for A level studentsA guide for A level students

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INTRODUCTION

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PERIOD 3 COMPOUNDSPERIOD 3 COMPOUNDS

CONTENTS

• Introduction

• Electronic configuration

• 1st Ionisation Energy

• Chlorides

• Oxides

• Reactions of metals

PERIOD 3PERIOD 3

ELECTRONIC ELECTRONIC CONFIGURATIONCONFIGURATION

ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION

1s2 2s2 2p6 3s1

1s2 2s2 2p6 3s2

1s2 2s2 2p6 3s2 3p1

1s2 2s2 2p6 3s2 3p2

1s2 2s2 2p6 3s2 3p3

1s2 2s2 2p6 3s2 3p4

1s2 2s2 2p6 3s2 3p5

1s2 2s2 2p6 3s2 3p6

Na

Mg

Al

Si

P

S

Cl

Ar

1s 2s 2p 3s 3p

The Aufbau principle states that… “ELECTRONS ENTER THE LOWEST AVAILABLE ENERGY LEVEL” . In period 3 the electrons fill the 3s orbital first, followed by the 3p orbitals. Notice how the electrons in the 3p orbitals remain unpaired, if possible, according to Hund’s Rule.

1st IONISATION 1st IONISATION ENERGYENERGY

FIRST IONISATION ENERGYFIRST IONISATION ENERGY

Na Mg Al Si P S Cl Ar

1500

1000

5003s 3p

3s 3p

There is a DROPDROP in the value for sulphur. The extra electron has paired up with one of the electrons already in one of the 3p orbitals. The repulsive force between the electrons means that less energy is required to remove one of them.

There is a DROPDROP in the value for aluminium because the extra electron has gone into a 3p orbital. The increased shielding makes the electron easier to remove.

Theoretically, the value should increase steadily across the period due to the increased nuclear charge. HOWEVER...

TRENDTREND

CHLORIDES OF PERIOD 3 ELEMENTSCHLORIDES OF PERIOD 3 ELEMENTS

NaCl MgCl2 AlCl3 SiCl4 PCl5

meltingpoint / K 1074 987 450 (sub) 203 435 (sub)

bonding ionic ionic covalent covalent covalent

structure giant giant simple simple simplelattice lattice molecule molecule molecule

solubility inwater very very hydrolysed hydrolysed hydrolysed

solution pH 7 6.5 5 0 0

SUMMARYSUMMARY

Most can be prepared by DIRECT COMBINATION by passing the gas overthe heated element.

e.g. Magnesium Mg(s) + Cl2(g) ——> MgCl2(s)

Aluminium 2Al(s) + 3Cl2(g) ——> 2AlCl3(s)


PREPARATIONPREPARATION

0 0 +2 -1

0 0 +3 -1

NaCl • ionic solid

• giant ionic lattice

• high melting point – strong electrostatic attraction between ions

• very soluble in water giving a neutral (pH = 7) solution

NaCl(s) ——> Na+(aq) + Cl¯(aq)


PROPERTIESPROPERTIES

Na+

Cl

MgCl2 • ionic solid


• high melting point – strong electrostatic attraction between ions

• soluble in water giving a slightly acidic (pH = 6.5) solution (due to greater charge density of Mg2+ ions)

MgCl2(s) ——> Mg2+(aq) + Cl¯(aq)



Mg2+ ClCl

AlCl3 • white solid

• high charge density of Al3+ favours covalency

• readily hydrolysed giving an acidic solution (pH = 5).

AlCl3(s) + 6H2O(l) ——> [Al(H2O)6]3+(aq) + 3Cl¯(aq)



Al ClCl

Cl

A LEWIS ACIDA LEWIS ACIDTRIGONAL PLANAR

TRIGONAL PLANAR

SiCl4 • simple covalent molecule

• volatile liquid

• fumes in moist air

• easily hydrolysed by water producing an acidic solution (pH= 0)

SiCl4(l) + 4H2O(l) ——> SiO2.2H2O(s) + 4HCl(aq)



Si ClCl

Cl

Cl

TETRAHEDRALTETRAHEDRAL

PCl5 • pale yellow solid

• exists as [PCl4+][PCl6¯] ; unusual for a non-metallic chloride

• hydrolysed by water giving an acidic solution (pH = 0)

PCl5(s) + 4H2O(l) ——> H3PO4(aq) + 5HCl(aq)



Na2O MgO Al2O3 SO2

Meltingpoint / K 1548 3125 2345 200

bonding ionic ionic ionic/cov covalent

structure giant giant giant simple lattice lattice lattice molecule

classification basic basic amphoteric acidic

solubility very sparingly insoluble reactsin water

solution pH 14 9 3

OXIDES OF PERIOD 3 ELEMENTSOXIDES OF PERIOD 3 ELEMENTS

SUMMARYSUMMARY

• metals produce basic oxides

• non-metals produce acidic oxides

• aluminium oxide is an amphoteric oxide (acidic and basic properties)

• ionic oxides have high melting points

• ionic oxides conduct electricity when molten

• most oxides can be prepared by direct combination (EXC. SO3)

2Mg(s) + O2(g) ——> 2MgO(s)

4Al(s) + 3O2(g) ——> 2Al2O3(s)

S(s) + O2(g) ——> SO2(g)


PREPARATIONPREPARATION

0 0 +2 -2

0 0 +4 -2

0 0 +3 -2

Na2O • white solid


• soluble in water to form a strongly alkaline solution (pH = 13-14)

Na2O(s) + H2O(l) ——> 2NaOH(aq)

• reacts with acids to form salts – A BASIC OXIDE

Na2O(s) + HCl(aq) ——> NaCl(aq) + H2O(l)



Na+

Na+O

2-

MgO • white solid


• sparingly soluble in water to form hydroxide (pH = 9)

(Low solubility is due to metal’s greater charge density)

MgO(s) + H2O(l) ——> Mg(OH)2(aq)

• reacts with acids to form salts – A BASIC OXIDE

MgO(s) + 2HCl(aq) ——> MgCl2(aq) + H2O(l)

Mg2+

O2-



Al2O3 • giant lattice with some covalent character

• insoluble in water

• AMPHOTERIC; it reacts with both acids and alkalis to give salts

with acids Al2O3(s) + 6HCl(aq) ——> 2AlCl3(aq) + 3H2O(l)

with alkalis Al2O3(s) + 2NaOH(aq) + 3H2O(l) ——> 2NaAl(OH)4(aq)



SO2 • simple covalent molecule

• soluble in water

• reacts with water to give a weak acidic solution (pH = 3)

SO2(g) + H2O(l) 2H+(aq) + SO32-(aq)

• converted to sulphur trioxide in the CONTACT PROCESS

ANGULAR / BENTANGULAR / BENTO S O



SO3 • simple covalent molecule

• reacts violently with water to give a strong acidic solution (pH = 0)

SO3(g) + H2O(l) ——> 2H+(aq) + SO42-(aq)

TRIGONAL PLANAR

TRIGONAL PLANAR



OS

O

O

METALS OF PERIOD 3METALS OF PERIOD 3

Sodium • vigorous reaction

• hydrogen evolved

• strong alkaline solution produced (pH = 14)

Na(s) + 2H2O(l) ——> 2NaOH(aq) + H2(g)

Magnesium • slow reaction with water

• weaker alkaline solution produced (pH 9-11)

Mg(s) + 2H2O(l) ——> Mg(OH)2(aq) + H2(g)

• very fast reaction with steam

Mg(s) + H2O(l) ——> MgO(S) + H2(g)

REACTION WITH WATERREACTION WITH WATER

© 2007 JONATHAN HOPTON & KNOCKHARDY PUBLISHING© 2007 JONATHAN HOPTON & KNOCKHARDY PUBLISHING

AN INTRODUCTION TOAN INTRODUCTION TO PERIOD PERIOD 3 COMPOUNDS3 COMPOUNDS

THE ENDTHE END

AN INTRODUCTION TO PERIOD 3 COMPOUNDS A guide for A level students KNOCKHARDY PUBLISHING.

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