periodic properties of elements in the periodic table
TRANSCRIPT
Periodic Law When elements
are arranged in order of atomic number, similar properties recur periodically.
LiNa
K
Atomic radii vs. Z
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
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
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
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.
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