1. Periodic Properties of Elements in the Periodic Table
Chapter 38

2. Periodic Table (Modern Form)

3. Periodic Law
The properties of elements are a periodic function of their atomic number
P = F(z)

4. Periodic Law
When elements are arranged in order of atomic number, similar properties recur periodically. Li Na K
Atomic radii vs. Z

5. Periodic Law
Atomic number
First Ionization Energy

6. Why Periodic Law? Chemical Type of and Bonding Physical and Atomic
properties
Type of
Bonding
and
structure
Atomic
properties
Atomic number

7. Ionization Energies Variations: Across a period Down the group H He NeLi Na K N Be B C O F Mg P Al Si S Cl Ca
Atomic number
First I.E.

8. Atomic radius K Ca Na Mg Li Be Ar H Ne He

9. Atomic Radius (pm) 1pm=1x10-12mH 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

10. Electronegativity F Electronegativity Cl H Ca Li Na K He Ne Ar
Atomic number

11. 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

12. Melting Points m.p./oC Atomic number C Si Ca He Ar Ne 4000 3000 2000
1000 Ca He Ar Ne
-1000
Atomic number

13. 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

14. Periodic Variation of Physical Properties
Structure & Bonding
Giant metallic  Giant covalent  Simple molecular

15. Periodic Variation of Chemical Properties
Formulae of hydrides, oxides, chlorides
Hydrolytic behaviours and explanations

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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.

22. Oxides Ionic Basic Na2O Ionic with Covalent character Amphoteric Al2O3
Acidic
CO2
SO2
NO2

23. 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)

24. Amphoteric Oxides BeO + 2H+  Be2+ + H2O
BeO + 2OH- + H2O  [Be(OH)4]2-
Al2O3 + 6H+  2Al3+ + 3H2O
Al2O3 + 2OH- + 3H2O  2[Al(OH)4]-

25. 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

26. 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.

27. 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)

28. 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.

29. Chlorides LiCl NaCl MgCl2 Ionic AlCl3 BeCl2 Intermediate with covalent
character
BCl3
CCl4
SiCl4
NCl3
PCl5
PCl3
OCl2
S2Cl2
SCl2
ClF
Cl2
Covalent

30. 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

31. 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

32. 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)

33. 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)

34. 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.

35. 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.

36. 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)

37. Check point 38-5 Give the equation for the reaction between the
following compounds with water:
AlCl3
Cl2O6

38. Past paper questions
Periodicity
1999 IIA 3c
2001 IIA 3c