Transcript Period 3 Knockhardy
AN INTRODUCTION TO
PERIOD 3 COMPOUNDS
A guide for A level students
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.
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PERIOD 3
CONTENTS
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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.
Na Mg Al Si P S Cl Ar 1s 2s 2p 3s 3p 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 3s 2 1s 2 2s 2 2p 6 3s 2 3p 1 1s 2 2s 2 2p 6 3s 2 3p 2 1s 2 2s 2 2p 6 3s 2 3p 3 1s 2 2s 2 2p 6 3s 2 3p 4 1s 2 2s 2 2p 6 3s 2 3p 5 1s 2 2s 2 2p 6 3s 2 3p 6
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.
1500 1000 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.
500 3s 3p 3s 3p Na Mg Al Si P S Cl Ar
CHLORIDES OF PERIOD 3 ELEMENTS
SUMMARY
NaCl MgCl 2 AlCl 3 SiCl 4 melting point / K bonding structure 1074 ionic giant lattice solubility in water solution pH very 7 987 450 (sub) ionic covalent 203 covalent giant simple simple lattice molecule molecule PCl 5 435 (sub) covalent simple molecule very hydrolysed hydrolysed hydrolysed 6.5
5 0 0
CHLORIDES OF PERIOD 3 ELEMENTS
PREPARATION
Most can be prepared by DIRECT COMBINATION the heated element.
by passing the gas over e.g.
Magnesium
0 0 +2 -1
Mg(s) + Cl 2 (g) ——> MgCl 2 (s) Aluminium
0 0 +3 -1
2Al(s) + 3Cl 2 (g) ——> 2AlCl 3 (s)
NaCl CHLORIDES OF PERIOD 3 ELEMENTS
PROPERTIES
• ionic solid Na + Cl • 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
MgCl 2 • ionic solid Cl Mg 2+ Cl • 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)
AlCl 3 CHLORIDES OF PERIOD 3 ELEMENTS
PROPERTIES
• white solid • high charge density of Al 3+ favours covalency A LEWIS ACID Cl Al Cl TRIGONAL PLANAR Cl • readily hydrolysed giving an acidic solution (pH = 5).
AlCl 3 (s) + 6H 2 O(l) ——> [Al(H 2 O) 6 ] 3+ (aq) + 3Cl¯(aq)
SiCl 4 CHLORIDES OF PERIOD 3 ELEMENTS
PROPERTIES
• simple covalent molecule • volatile liquid • fumes in moist air Cl TETRAHEDRAL Cl Si Cl Cl • 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)
PCl 5 CHLORIDES OF PERIOD 3 ELEMENTS
PROPERTIES
• 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)
OXIDES OF PERIOD 3 ELEMENTS
SUMMARY
Na 2 O MgO Al 2 O 3 SO 2 Melting point / K bonding structure classification solubility in water solution pH 1548 ionic giant lattice basic very 14 3125 ionic giant lattice basic sparingly 9 2345 ionic/cov giant lattice amphoteric insoluble 200 covalent simple molecule acidic reacts 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. SO 3 )
0 0 +2 -2
2Mg(s) + O 2 (g) ——> 2MgO(s)
0 0 +3 -2
4Al(s) + 3O 2 (g) ——> 2Al 2 O 3 (s)
0 0 +4 -2
S(s) + O 2 (g) ——> SO 2 (g)
Na 2 O OXIDES OF PERIOD 3 ELEMENTS
PROPERTIES
• 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) Na + O 2 Na +
MgO OXIDES OF PERIOD 3 ELEMENTS
PROPERTIES
• 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-
Al 2 O 3 OXIDES OF PERIOD 3 ELEMENTS
PROPERTIES
• giant lattice with some covalent character • insoluble in water • AMPHOTERIC ; it reacts with both acids and alkalis to give salts with acids with alkalis Al 2 O 3 (s) + 6HCl(aq) ——> 2AlCl 3 (aq) + 3H 2 O(l) Al 2 O 3 (s) + 2NaOH(aq) + 3H 2 O(l) ——> 2NaAl(OH) 4 (aq)
SO 2 OXIDES OF PERIOD 3 ELEMENTS
PROPERTIES
• simple covalent molecule O S O ANGULAR / BENT • 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
SO 3 OXIDES OF PERIOD 3 ELEMENTS
PROPERTIES
• simple covalent molecule O S TRIGONAL PLANAR O O • 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)
Sodium Magnesium METALS OF PERIOD 3
REACTION WITH WATER
• vigorous reaction • hydrogen evolved • strong alkaline solution produced (pH = 14) Na(s) + 2H 2 O(l) ——> 2NaOH(aq) + H 2 (g) • 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)