Periodic Properties Of Elements In The Periodic Table

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.

Atomic radii vs. Z K Na Li

Periodic Law First Ionization Energy Atomic number

Why Periodic Law? Chemical and Physical properties

Type of Bonding and structure

Atomic properties

Atomic number

Ionization Energies

First I.E.

Variations: 2. Across a period 3. Down the group Ne

He

N Be

H Li

C B

Ar

F O

P Mg

Na

Al

Si

Atomic number

S Cl

Ca K

Atomic radius K Ca Na Mg

Li Be H

He

Ne

Ar

Atomic Radius (pm) 1pm=1x10-12m H 37

He 54

Li Be 156 105

B 91

C 77

N 71

O 60

F 67

Ne 80

Na Mg 186 160

Al Si P S Cl 143 117 111 104 99

Ar 96

K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 231 197 161 154 131 125 118 125 125 124 128 133 123 122 116 115 114 99 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 243 215 180 161 147 136 135 132 132 138 144 149 151 140 145 139 138 109 Cs Ba 265 210

Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 154 143 137 138 134 136 139 144 147 189 175 155 167 145

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 187 183 182 181 181 180 199 179 176 175 174 173 173 194 172

Electronegativity

Electronegativity F Cl H Li He

Na

K

Ne Ar Atomic number

Ca

Electronegativity Increase in electronegativity H 2.1

Decrease Li 1.0 Na 0.9

Be 1.5 Mg 1.2

K Al 0.8 1.0

He N O F Ne B C 2.0 2.5 3.0 3.5 4.0 P S Cl Al Si Ar 1.5 1.8 2.1 2.5 3.0 -

Melting Points m.p./oC C

4000 3000

Si

2000 1000 0 -1000 0

Ca He

Ar

Ne 5

10

15

20

Atomic number

Melting Points Increase H

He

-259

-270

B

C

N

O

F

Li

Be

180

1280

2300 3730

-210 -218 -220

Na

Mg

Al

P

S

Cl

44.2

119

-101

97.8

K

650

Ca

63.7 850

Si

660 1410

Unit: oC

Ne -249

Ar -189

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

Period 3

NaH MgH2 AlH3 Ionic

BeH2

B2H6 CH4 NH3 H2O HF

Covalent with some ionic character

SiH4 PH3 H2S HCl Typically Polar Covalent covalent

Hydrides Bonding Ionic

Hydrolytic behaviour NaH + H2O → NaOH + H2 (H- + H2O → OH- + H2)

Covalent withBeH2 + 2H2O → Be(OH)2 + 2H2 ionic character MgH2+ 2H2O → Mg(OH)2 + H2 B2H6 + 6H2O → 2H3BO3 + 6H2 AlH3 + 3H2O → Al(OH)3 + 3H2

Be(OH)2, Mg(OH)2, Al(OH)3 are alkaline H3BO3 is acidic

Hydrides Typically CH4 does not dissolve nor react Covalent SiH4 reacts to give SiO2.2H2O + H2 PH3 very slight soluble H Si H

H

H H

:OH2

Si H

H

OH

+ H2

etc

Hydrides Polar covalent

NH3 + H2O → NH4+ + OHH2S + H2O → H3O+ + HSHF + H2O → H3O+ + FHCl + H2O → H3O+ + Cl-

Note: From gp4 to gp7 Acidity increases because polarity of bond increase

Check point 38-3 H-O-H + H2O:

+

:NH3 H-Cl

OH- + NH4+ 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 Ionic with Covalent character Covalent

Basic

Na2O

Amphoteric

Al2O3

Acidic

CO2 SO2 NO2

Ionic Oxides O2- + H2O → 2OHNa2O(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]2Al2O3 + 6H+ → 2Al3+ + 3H2O Al2O3 + 2OH- + 3H2O → 2[Al(OH)4]-

Covalent Oxides Mechanism of the Hydrolytic behaviour of covalent oxides: O=Xδ+ :O-H H

[O-X-OH]- + H+

CO2 + H2O  H2CO3  H+ + HCO3SO2 + H2O  H2SO3  H+ + HSO32NO2 + 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) O

O Cl

O

O Cl

O O Cl2O7(g)/(l)

O

+

O

O

Cl O

O Cl2O7(s)

O Cl O

O

-

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

BeCl2

NaCl MgCl2 Ionic

BCl3 CCl4 NCl3 OCl2 ClF AlCl3

Intermediate with covalent character

SiCl4 PCl5 S2Cl2 Cl2 PCl3 SCl2 Covalent

Ionic chlorides 

Group IA 



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. Be2+

:O

BeCl2 + 2H2O

H

:OH2

H Be(OH)2 + HCl

AlCl3 + 3H2O → Al(OH)3 + 3HCl

Covalent chlorides Group IIIA BCl3

Cl B

:OH2

δ+

Cl

Cl

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 C Cl

Cl Cl

Si Cl

Cl Cl

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 H

:Nδ-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