periodic properties of elements in the periodic table chapter 38
Post on 26-Mar-2015
226 Views
Preview:
TRANSCRIPT
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
NaK
Atomic radii vs. Z
Periodic Law
Atomic number
First Ion
ization
En
ergy
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:1. Across a period2. Down the group
Atomic radius
HHe
Li
Na
NeAr
K
Be
Mg
Ca
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
125
Co
125
Ni
124
Cu
128
Zn
133
Ga
123
Ge
122
As
116
Se
115
Br
114
Kr
99
Rb
243
Sr
215
Y
180
Zr
161
Nb
147
Mo
136
Tc
135
Ru
132
Rh
132
Pd
138
Ag
144
Cd
149
In
151
Sn
140
Sb
145
Te
139
I
138
Xe
109
Cs
265
Ba
210
Hf
154
Ta
143
W
137
Re
138
Os
134
Ir
136
Pt
139
Au
144
Hg
147
Tl
189
Pb
175
Bi
155
Po
167
At
145
Rn
La
187
Ce
183
Pr
182
Nd
181
Pm
181
Sm
180
Eu
199
Gd
179
Tb
176
Dy
175
Ho
174
Er
173
Tm
173
Yb
194
Lu
172
Atomic Radius (pm) 1pm=1x10-12m
Electronegativity
H
He Ne Ar
F
Cl
Li Na KCaEl
ectr
oneg
ativ
ity
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
SiH
H HH
:OH2 SiH
HOH
H
+ 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 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=X+ :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
a. 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 h
eated. 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
ClClB+
: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:N-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:
a. AlCl3b. Cl2O6
Past paper questions
Periodicity
1999 IIA 3c2001 IIA 3c
top related