The S-Block Elements: Dr. Vatsala Soni PGGC Sector - 11 Chandigarh
The S-Block Elements: Dr. Vatsala Soni PGGC Sector - 11 Chandigarh
The S-Block Elements: Dr. Vatsala Soni PGGC Sector - 11 Chandigarh
IA IIA
Li Be
Na Mg
K Ca
Rb Sr
IA Alkali metals
Cs Ba
IIA Alkaline Earth
Fr Ra
metals
Chapter summary
Characteristic properties of the s-block elements
Variation in properties of the s-block elements
Variation in properties of the s-block compounds
Uses of compounds of the s-block elements
Characteristic properties of s-block
elements
Metallic character
Low electronegativity
Basic oxides, hydroxides
Ionic bond with fixed oxidation states
Characteristic flame colours
Weak tendency to from complex
Metallic character
. .-
.. .. 2-
:O:.O:
:O:O: Li does not form
.. ..
.. .. peroxide or super oxide
Super oxide Li2O2 Li2O + ½ O2
Peroxide ion
Hydroxides
Group I
hydroxides Li Na K Rb Cs
Group II
hydroxide Be Mg Ca Sr Ba
HCl(aq) sample
Weak tendency to form complex
:NH3
s-block metal ions have
no low energy vacant H3N: :NH3
orbital available for Co
bonding with lone pairs H3N: :NH3
of surrounding ligands,
:NH3
they rarely form
complexes.
Variation in properties of elements
Atomic radii
Ionization enthalpies
Hydration enthalpies
Melting points
Reactions with oxygen, water, hydrogen and
chlorine
Atomic radii (nm)
Li 0.152 Be 0.112
Na 0.186 Mg 0.160 Fr
K 0.231 Ca 0.197
Ra
Li
Rb 0.244 Sr 0.215
Cs 0.262 Ba 0.217 Be
Fr 0.270 Ra 0.220
Ionization Enthapy
1st I.E.
2000
600 Be+
Li
500 Na 1500
2nd IE
400 K
Rb Ca+
Cs 1000
300 Be Ba+
500 Ca
1st IE Ba
Ionization Enthalpy
Group I
Group II
-600
M+ -300
-2250
-600
-2000
-1750
-300
-1500
General trends:
1. On going down both groups, hydration enthalpy
decreases.
(As the ions get larger, the charge density of the
ions decreases, the electrostatic attraction between
ions and water molecules gets smaller.)
Be
1250
1000
Ca
Sr
750 Ba
Mg
500
250 Li
Na K Rb
Cs
10 20 30 40 50 60
Variation in Melting Points
Structure .. 2- .. .. 2- . .-
:O: :O-O: :O:.O:
.. .. .. .. ..
Formed by Li and Na and Ba K, Rb, Cs
Group II
Reaction with water
M(s) M+(aq) + e-
H2O(l) + e- OH-(aq) + ½ H2(g)
Li -3.05 volt
Na -2.71
K -2.93 Be -1.85 volt
Rb -2.99 Mg -2.38
Cs -3.20 Ca -2.87
Sr -2.89
Ba -2.90
+ -
Decreasing Increasing
+ -
polarizing stability
power
+ -
Explanation of Thermal Stability
O
Mg2+ - :O C Mg2+ O2- + CO2
O:-
-:O H
Mg2+ Mg2+ O2- + H2O
-:O H
Explanation of Thermal Stability
MgCO3 MgO
BaO
MgO
BaCO3 BaO
Relative solubility of Group II
hydroxides
Ba(OH)2 15 x 10-3
Solubility of Group II sulphates
aqueous
MX(s) M+(aq) + X-(aq)
H solution
M+(g) + X-(g)
MgSO4 SrSO4
Explanation of solubility
Paper industry
Sodium hydrocarbonate
Baking powder
Soft drink
Uses of s-block compounds
Sodium hydroxide
Manufacture of soaps, dyes, paper and drugs
To make rayon and important chemicals
Magnesium hydroxide
Milk of magnesia, an antacid
Calcium hydroxide
To neutralize acids in waste water treatment
Strontium compound
Fireworks, persistent intense red flame
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