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.

LiNa

K

Atomic radii vs. Z

Periodic Law

Atomic number

First Ion

ization E

nergy

Why Periodic Law?

Chemicaland Physicalproperties

Type ofBondingandstructure

Atomicproperties

Atomic number

Ionization Energies

H

HeNe

Ar

Li Na K

N

Be

BC O

F

MgP

AlSi S Cl

Ca

Atomic number

First I.E

.

Variations:2. Across a period3. Down the group

Atomic radius

HHe

Li

Na

NeAr

K

Be

Mg

Ca

Lu

172

Yb

194

Tm

173

Er

173

Ho

174

Dy

175

Tb

176

Gd

179

Eu

199

Sm

180

Pm

181

Nd

181

Pr

182

Ce

183

La

187

RnAt

145

Po

167

Bi

155

Pb

175

Tl

189

Hg

147

Au

144

Pt

139

Ir

136

Os

134

Re

138

W

137

Ta

143

Hf

154

Ba

210

Cs

265

Xe

109

I

138

Te

139

Sb

145

Sn

140

In

151

Cd

149

Ag

144

Pd

138

Rh

132

Ru

132

Tc

135

Mo

136

Nb

147

Zr

161

Y

180

Sr

215

Rb

243

Kr

99

Br

114

Se

115

As

116

Ge

122

Ga

123

Zn

133

Cu

128

Ni

124

Co

125

Fe

125

Mn

118

Cr

125

V

131

Ti

154

Sc

161

Ca

197

K

231

Ar

96

Cl

99

S

104

P

111

Si

117

Al

143

Mg

160

Na

186

Ne

80

F

67

O

60

N

71

C

77

B

91

Be

105

Li

156

He

54

H

37

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

Electronegativity

H

He Ne Ar

F

Cl

Li Na KCa

Elec

tron

e gat

ivit y

Atomic number

Electronegativity

H2.1

Li1.0

Be1.5

Na0.9

Mg1.2

Al1.0

K0.8

B2.0

C2.5

N3.0

O3.5

F4.0

Al1.5

Si1.8

P2.1

S2.5

Cl3.0

Ne -

Ar -

He-

Increase in electronegativity

Decrease

Melting Points

m.p./oC

1000

2000

3000

4000

0 5 10 15 20

Atomic number

-1000

0

C

Si

He Ne Ar

Ca

Melting Points

H-259

Li180

Be1280

Na97.8

Mg650

Ca850

K63.7

B2300

C3730

N-210

O-218

F-220

Al660

Si1410

P44.2

S119

Cl-101

Ne -249

Ar -189

He-270

Unit: oC

Increase

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

Li Be B C N O F Ne Na Mg Al Si P S Cl Ar

6

4

2

Moles of Cl atoms per mole of atoms of element

Hydrides

Period 2 LiH BeH2 B2H6 CH4 NH3 H2O HF

Period 3 NaH MgH2 AlH3 SiH4 PH3 H2S HCl

Ionic Covalentwith someioniccharacter

TypicallyCovalent

Polarcovalent

Hydrides

Bonding Hydrolytic behaviour

Ionic NaH + H2O → NaOH + H2

(H- + H2O → OH- + H2)

Be(OH)2, Mg(OH)2, Al(OH)3 are alkalineH3BO3 is acidic

Covalent withionic character

BeH2 + 2H2O → Be(OH)2 + 2H2

MgH2+ 2H2O → Mg(OH)2 + H2

B2H6 + 6H2O → 2H3BO3 + 6H2

AlH3 + 3H2O → Al(OH)3 + 3H2

Hydrides

TypicallyCovalent

CH4 does not dissolve nor react

SiH4 reacts to give SiO2.2H2O + H2

PH3 very slight soluble

Si

H

H HH

:OH2 Si

H

HOH

H

+ H2etc

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 notdissolve nor react with water.

Oxides

Ionic

Ionic withCovalent character

Amphoteric Al2O3

Covalent Acidic CO2

SO2

NO2

Basic Na2O

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

Al2O3 + 6H+ → 2Al3+ + 3H2OAl2O3 + 2OH- + 3H2O → 2[Al(OH)4]-

BeO + 2H+ → Be2+ + H2OBeO + 2OH- + H2O → [Be(OH)4]2-

Covalent Oxides

O=Xδ+ :O-H H [O-X-OH]- + H+

Mechanism of the Hydrolytic behaviourof covalent oxides:

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)

ClO O

O O

ClO

OO

Cl2O7(g)/(l)

ClO O

O O

ClO

OO

+ -

Cl2O7(s)

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

Intermediatewith covalentcharacter

BCl3 CCl4

SiCl4

NCl3

PCl5PCl3

OCl2

S2Cl2SCl2

ClF

Cl2

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 chloridesBeCl2 and AlCl3 :

Be2+ and Al3+

High charge/size ratio, strong polarizing power,cation hydrolysis.

Be2+ :OH

H:OH2

Be(OH)2 + HClBeCl2 + 2H2O

AlCl3 + 3H2O → Al(OH)3 + 3HCl

Covalent chlorides

Group IIIA BCl3 Cl

ClClBδ+ :OH2

Due to presence of vacant orbital and the polarB-Cl bond.

BCl3 reacts vigorously with water to giveboric acid, H3BO3 and HCl.

BCl3(l) + 3H2O(l) → H3BO3 (aq) + 3HCl(aq)

Covalent chloridesGroup 4A : CCl4 and SiCl4

Cl

Cl ClClSi

Cl

Cl ClClC

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

N does not have low-lying vacant orbital,it hydrolyses through the donation of lone pairelectron of N atom to the H atom of water molecule.

:OH

H:Nδ-Cl3

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 3c2001 IIA 3c