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

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... Navigation is achieved by... either clicking on the grey arrows at the foot of each page orusing the left and right arrow keys on the keyboard KNOCKHARDY PUBLISHING PERIOD 3 COMPOUNDS

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

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.

1st IONISATION ENERGY

FIRST IONISATION ENERGY Na Mg Al Si P S Cl Ar s 3p DROP 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. DROP 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. Theoretically, the value should increase steadily across the period due to the increased nuclear charge. HOWEVER... TREND

CHLORIDES OF PERIOD 3 ELEMENTS NaCl MgCl 2 AlCl 3 SiCl 4 PCl 5 melting point / K (sub) (sub) bondingionic ionic covalent covalentcovalent structuregiant giantsimple simple simple lattice lattice molecule moleculemolecule solubility in watervery very hydrolysed hydrolysed hydrolysed solution pH SUMMARY

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

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) CHLORIDES OF PERIOD 3 ELEMENTS PROPERTIES Na + Cl

MgCl 2 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 Mg 2+ ions) MgCl 2 (s) ——> Mg 2+ (aq) + Cl¯(aq) CHLORIDES OF PERIOD 3 ELEMENTS PROPERTIES Mg 2+ Cl

AlCl 3 white solid high charge density of Al 3+ favours covalency readily hydrolysed giving an acidic solution (pH = 5). AlCl 3 (s) + 6H 2 O(l) ——> [Al(H 2 O) 6 ] 3+ (aq) + 3Cl¯(aq) CHLORIDES OF PERIOD 3 ELEMENTS PROPERTIES Al Cl A LEWIS ACID TRIGONAL PLANAR

SiCl 4 simple covalent molecule volatile liquid fumes in moist air easily hydrolysed by water producing an acidic solution (pH= 0) SiCl 4 (l) + 4H 2 O(l) ——> SiO 2.2H 2 O(s) + 4HCl(aq) CHLORIDES OF PERIOD 3 ELEMENTS PROPERTIES Si Cl TETRAHEDRAL

PCl 5 pale yellow solid exists as [PCl 4 + ][PCl 6 ¯] ; unusual for a non-metallic chloride hydrolysed by water giving an acidic solution (pH = 0) PCl 5 (s) + 4H 2 O(l) ——> H 3 PO 4 (aq) + 5HCl(aq) CHLORIDES OF PERIOD 3 ELEMENTS PROPERTIES

Na 2 O MgO Al 2 O 3 SO 2 Melting point / K bonding ionic ionic ionic/cov covalent structure giant giant giant simple lattice lattice lattice molecule classificationbasic basic amphoteric acidic solubilityvery sparingly insoluble reacts in water solution pH OXIDES OF PERIOD 3 ELEMENTS SUMMARY

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. SO 3 ) 2Mg(s) + O 2 (g) ——> 2MgO(s) 4Al(s) + 3O 2 (g) ——> 2Al 2 O 3 (s) S(s) + O 2 (g) ——> SO 2 (g) OXIDES OF PERIOD 3 ELEMENTS PREPARATION

Na 2 O white solid giant ionic lattice soluble in water to form a strongly alkaline solution (pH = 13-14) Na 2 O(s) + H 2 O(l) ——> 2NaOH(aq) reacts with acids to form salts – A BASIC OXIDE Na 2 O(s) + HCl(aq) ——> NaCl(aq) + H 2 O(l) OXIDES OF PERIOD 3 ELEMENTS PROPERTIES Na + + O 2-

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) + H 2 O(l) ——> Mg(OH) 2 (aq) reacts with acids to form salts – A BASIC OXIDE MgO(s) + 2HCl(aq) ——> MgCl 2 (aq) + H 2 O(l) Mg 2+ O 2- OXIDES OF PERIOD 3 ELEMENTS PROPERTIES

Al 2 O 3 giant lattice with some covalent character insoluble in water AMPHOTERIC; it reacts with both acids and alkalis to give salts with acidsAl 2 O 3 (s) + 6HCl(aq) ——> 2AlCl 3 (aq) + 3H 2 O(l) with alkalis Al 2 O 3 (s) + 2NaOH(aq) + 3H 2 O(l) ——> 2NaAl(OH) 4 (aq) OXIDES OF PERIOD 3 ELEMENTS PROPERTIES

SO 2 simple covalent molecule soluble in water reacts with water to give a weak acidic solution (pH = 3) SO 2 (g) + H 2 O(l) 2H + (aq) + SO 3 2- (aq) converted to sulphur trioxide in the CONTACT PROCESS ANGULAR / BENT O S O OXIDES OF PERIOD 3 ELEMENTS PROPERTIES

SO 3 simple covalent molecule reacts violently with water to give a strong acidic solution (pH = 0) SO 3 (g) + H 2 O(l) ——> 2H + (aq) + SO 4 2- (aq) TRIGONAL PLANAR OXIDES OF PERIOD 3 ELEMENTS PROPERTIES O S O O

METALS OF PERIOD 3 Sodium vigorous reaction hydrogen evolved strong alkaline solution produced (pH = 14) Na(s) + 2H 2 O(l) ——> 2NaOH(aq) + H 2 (g) Magnesium slow reaction with water weaker alkaline solution produced (pH 9-11) Mg(s) + 2H 2 O(l) ——> Mg(OH) 2 (aq) + H 2 (g) very fast reaction with steam Mg(s) + H 2 O(l) ——> MgO(S) + H 2 (g) REACTION WITH WATER

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