Periodic Properties of Elements in the Periodic Table Chapter 38
Periodic Table (Modern Form)
Periodic Law The properties of elements are a periodic function of their atomic number P = F(z)
Periodic Law When elements are arranged in order of atomic number, similar properties recur periodically. Li Na K Atomic radii vs. Z
Periodic Law Atomic number First Ionization Energy
Why Periodic Law? Chemical Type of and Bonding Physical and Atomic properties Type of Bonding and structure Atomic properties Atomic number
Ionization Energies Variations: Across a period Down the group H He Ne Li Na K N Be B C O F Mg P Al Si S Cl Ca Atomic number First I.E.
Atomic radius K Ca Na Mg Li Be Ar H Ne He
Atomic Radius (pm) 1pm=1x10-12m H 37 He 54 Li 156 Be 105 B 91 C 77 N 71 O 60 F 67 Ne 80 Na 186 Mg 160 Al 143 Si 117 P 111 S 104 Cl 99 Ar 96 K 231 Ca 197 Sc 161 Ti 154 V 131 Cr 125 Mn 118 Fe Co Ni 124 Cu 128 Zn 133 Ga 123 Ge 122 As 116 Se 115 Br 114 Kr Rb 243 Sr 215 Y 180 Zr Nb 147 Mo 136 Tc 135 Ru 132 Rh Pd 138 Ag 144 Cd 149 In 151 Sn 140 Sb 145 Te 139 I Xe 109 Cs 265 Ba 210 Hf Ta W 137 Re Os 134 Ir Pt Au Hg Tl 189 Pb 175 Bi 155 Po 167 At Rn La 187 Ce 183 Pr 182 Nd 181 Pm Sm Eu 199 Gd 179 Tb 176 Dy Ho 174 Er 173 Tm Yb 194 Lu 172
Electronegativity F Electronegativity Cl H Ca Li Na K He Ne Ar Atomic number
Electronegativity Increase in electronegativity H 2.1 Li 1.0 Be 1.5 Na 0.9 Mg 1.2 Al K 0.8 B 2.0 C 2.5 N 3.0 O 3.5 F 4.0 Si 1.8 P S Cl Ne - Ar He Decrease
Melting Points m.p./oC Atomic number C Si Ca He Ar Ne 4000 3000 2000 1000 Ca He Ar Ne -1000 0 5 10 15 20 Atomic number
Melting Points Increase H Li Be Na Mg Ca K B C N O F Al Si P S Cl Ne -259 Li 180 Be 1280 Na 97.8 Mg 650 Ca 850 K 63.7 B 2300 C 3730 N -210 O -218 F -220 Al 660 Si 1410 P 44.2 S 119 Cl -101 Ne -249 Ar -189 He -270 Unit: oC
Periodic Variation of Physical Properties Structure & Bonding Giant metallic Giant covalent Simple molecular
Periodic Variation of Chemical Properties Formulae of hydrides, oxides, chlorides Hydrolytic behaviours and explanations
Peiodicity in formulae Moles of Cl atoms per mole of atoms of element 6 4 2 Li Be B C N O F Ne Na Mg Al Si P S Cl Ar
Hydrides Period 2 LiH BeH2 B2H6 CH4 NH3 H2O HF Period 3 NaH MgH2 AlH3 SiH4 PH3 H2S HCl Covalent with some ionic character Ionic Typically Covalent Polar covalent
Hydrides Bonding Hydrolytic behaviour Ionic NaH + H2O NaOH + H2 (H- + H2O OH- + H2) Be(OH)2, Mg(OH)2, Al(OH)3 are alkaline H3BO3 is acidic Covalent with ionic character BeH2 + 2H2O Be(OH)2 + 2H2 MgH2+ 2H2O Mg(OH)2 + H2 B2H6 + 6H2O 2H3BO3 + 6H2 AlH3 + 3H2O Al(OH)3 + 3H2
Hydrides CH4 does not dissolve nor react Typically Covalent SiH4 reacts to give SiO2.2H2O + H2 PH3 very slight soluble Si H :OH2 OH + H2 etc
Hydrides Polar covalent NH3 + H2O NH4+ + OH- H2S + H2O H3O+ + HS- HF + H2O H3O+ + F- HCl + H2O H3O+ + Cl- Note: From gp4 to gp7 Acidity increases because polarity of bond increase
Check point 38-3 H-O-H :NH3 OH- + NH4+ + H2O: + H-Cl H3O+ + Cl- N is more electronegative, hence more basic than Cl. It reacts with water by donating its lone pair electron. CH4 , due to its non-polar covalent bond, it does not dissolve nor react with water.
Oxides Ionic Basic Na2O Ionic with Covalent character Amphoteric Al2O3 Acidic CO2 SO2 NO2
Ionic Oxides O2- + H2O 2OH- Na2O(s) + H2O(l) 2NaOH(aq) Li2O(s) + H2O(l) 2LiOH(aq) MgO(s) + H2O(l) Mg(OH)2(s)
Amphoteric Oxides BeO + 2H+ Be2+ + H2O BeO + 2OH- + H2O [Be(OH)4]2- Al2O3 + 6H+ 2Al3+ + 3H2O Al2O3 + 2OH- + 3H2O 2[Al(OH)4]-
Covalent Oxides Mechanism of the Hydrolytic behaviour of covalent oxides: :O-H H O=X+ [O-X-OH]- + H+ CO2 + H2O H2CO3 H+ + HCO3- SO2 + H2O H2SO3 H+ + HSO3- 2NO2 + H2O HNO3 + HNO2
Covalent Oxides P4O6 and P4O10 : P4O6(s) + 6H2O(l), cold 4H3PO3(aq) P4O6(s) + 6H2O(l), hot 3H3PO4(aq) + PH3(g) P4O10(s) + 6H2O(l) 4H3PO4(aq) The actual reactions are complicated. The products formed depend on the amount of water present and the conditions of reaction.
Covalent Oxides Group VIIA: F2O, Cl2O and Cl2O7 F2O(g) + H2O(l) 2HF(aq) + O2(g) Cl2O(g) + H2O(l) 2HOCl(aq) Cl2O7(l) + H2O(l) 2HClO4(aq) Cl O + - Cl2O7(s) Cl O Cl2O7(g)/(l)
Check point 38-4 SiO2 does not react with water. The giant covalent structure has high lattice energy. It is not possible to break it down in aqueous solution.
Chlorides LiCl NaCl MgCl2 Ionic AlCl3 BeCl2 Intermediate with covalent character BCl3 CCl4 SiCl4 NCl3 PCl5 PCl3 OCl2 S2Cl2 SCl2 ClF Cl2 Covalent
Ionic chlorides Group IA Group IIA LiCl, NaCl are not hydrolysed in aqueous solution, neutral solution formed when dissolved. NaCl (s) Na+(aq) + Cl-(aq), LiCl (s) Li+(aq) + Cl-(aq) Group IIA MgCl2 is not hydrolysed. Hydrated crystals undergoes hydrolysis when heated. MgCl2.6H2O MgCl(OH) + 5H2O + HCl
Intermediate chlorides BeCl2 and AlCl3 : Be2+ and Al3+ High charge/size ratio, strong polarizing power, cation hydrolysis. :O H :OH2 Be2+ Be(OH)2 + HCl BeCl2 + 2H2O AlCl3 + 3H2O Al(OH)3 + 3HCl
Covalent chlorides Group IIIA BCl3 Cl B+ :OH2 Due to presence of vacant orbital and the polar B-Cl bond. BCl3 reacts vigorously with water to give boric acid, H3BO3 and HCl. BCl3(l) + 3H2O(l) H3BO3 (aq) + 3HCl(aq)
Covalent chlorides Group 4A : CCl4 and SiCl4 Cl Cl Si C CCl4 does not hydrolyzed by water SiCl4 hydrolyzes. SiCl4(g) + 4H2O(l) SiO2.2H2O(s) + 4HCl(aq)
Covalent chlorides Group VA: NCl3 NCl3(l) + 3H2O(l) NH3(aq) + 3HOCl(aq) chloric(I) acid :O H :N-Cl3 N does not have low-lying vacant orbital, it hydrolyses through the donation of lone pair electron of N atom to the H atom of water molecule.
Covalent chlorides Group VA: PCl3 and PCl5 PCl3(l) + 3H2O(l) H3PO3(aq) + 3HCl(aq) PCl5(s) + 4H2O(l) H3PO4(aq) + 5HCl(aq) P is less electronegative than Cl. PCl3 and PCl5 hydrolyze by accepting the electron pair from water molecule.
Covalent chlorides Group VI: SCl2 , S2Cl2 SCl2(g) + H2O(l) HSCl(aq) + HOCl(aq) S2Cl2(l) + 2H2O(l) H2S(g) + SO2(g) + 2HCl(aq) Group VII: FCl, Cl2 FCl(g) + H2O(l) HF(aq) + HOCl(aq) Cl2(g) + H2O(l) HCl(aq) + HOCl(aq)
Check point 38-5 Give the equation for the reaction between the following compounds with water: AlCl3 Cl2O6
Past paper questions Periodicity 1999 IIA 3c 2001 IIA 3c