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

KNOCKHARDY PUBLISHING PERIOD 3 COMPOUNDS INTRODUCTION This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards. Individual students may use the material at home for revision purposes or it may be used for classroom teaching if an interactive white board is available. Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at... www.knockhardy.org.uk/sci.htm Navigation is achieved by... either clicking on the grey arrows at the foot of each page or using the left and right arrow keys on the keyboard

PERIOD 3 CONTENTS Introduction Electronic configuration 1st Ionisation Energy Chlorides Oxides Reactions of metals

ELECTRONIC CONFIGURATION

ELECTRONIC CONFIGURATION 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. 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

1st IONISATION ENERGY

FIRST IONISATION ENERGY TREND Theoretically, the value should increase steadily across the period due to the increased nuclear charge. HOWEVER... There is a DROP in the value for aluminium because the extra electron has gone into a 3p orbital. The increased shielding makes the electron easier to remove. Na Mg Al Si P S Cl Ar 1500 1000 500 There is a DROP 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. 3s 3p 3s 3p

CHLORIDES OF PERIOD 3 ELEMENTS SUMMARY NaCl MgCl2 AlCl3 SiCl4 PCl5 melting point / K 1074 987 450 (sub) 203 435 (sub) bonding ionic ionic covalent covalent covalent structure giant giant simple simple simple lattice lattice molecule molecule molecule solubility in water very very hydrolysed hydrolysed hydrolysed solution pH 7 6.5 5 0 0

CHLORIDES OF PERIOD 3 ELEMENTS PREPARATION Most can be prepared by DIRECT COMBINATION by passing the gas over the heated element. e.g. Magnesium Mg(s) + Cl2(g) ——> MgCl2(s) Aluminium 2Al(s) + 3Cl2(g) ——> 2AlCl3(s) +2 -1 +3 -1

CHLORIDES OF PERIOD 3 ELEMENTS PROPERTIES 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) Cl Na +

CHLORIDES OF PERIOD 3 ELEMENTS PROPERTIES MgCl2 • ionic solid • giant ionic lattice • 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) Cl Cl Mg 2+

CHLORIDES OF PERIOD 3 ELEMENTS PROPERTIES 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 Cl A LEWIS ACID TRIGONAL PLANAR

CHLORIDES OF PERIOD 3 ELEMENTS PROPERTIES 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 Cl TETRAHEDRAL

CHLORIDES OF PERIOD 3 ELEMENTS PROPERTIES 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)

OXIDES OF PERIOD 3 ELEMENTS SUMMARY Na2O MgO Al2O3 SO2 Melting point / 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 reacts in water solution pH 14 9 3

OXIDES OF PERIOD 3 ELEMENTS PREPARATION • 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) +2 -2 +3 -2 +4 -2

OXIDES OF PERIOD 3 ELEMENTS PROPERTIES Na2O • white solid • giant ionic lattice • 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 + O 2- Na +

OXIDES OF PERIOD 3 ELEMENTS PROPERTIES MgO • white solid • giant ionic lattice • 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) Mg 2+ O 2-

OXIDES OF PERIOD 3 ELEMENTS PROPERTIES 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)

OXIDES OF PERIOD 3 ELEMENTS PROPERTIES 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 O S ANGULAR / BENT

OXIDES OF PERIOD 3 ELEMENTS PROPERTIES SO3 • simple covalent molecule • reacts violently with water to give a strong acidic solution (pH = 0) SO3(g) + H2O(l) ——> 2H+(aq) + SO42-(aq) O S TRIGONAL PLANAR

Mg(s) + H2O(l) ——> MgO(S) + H2(g) METALS OF PERIOD 3 REACTION WITH WATER 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)

© 2007 JONATHAN HOPTON & KNOCKHARDY PUBLISHING AN INTRODUCTION TO PERIOD 3 COMPOUNDS THE END © 2007 JONATHAN HOPTON & KNOCKHARDY PUBLISHING