S-block Elements: Brief Details of Alkali and Alkaline earth elements

S-block Elements: Brief Details of Alkali and Alkaline Earth Elements
CHC-203 Inorganic Chemistry

1. S-block Elements
KCa
RbSr
CsBa
FrRa
LiBe
NaMg
H
IA
IIA1
2
3
4
5
6
7
Groups
S-block elements are those elements in Groups I and
II of the periodic table, where the last electron added
to an atom enters an s orbital.
Group Common Name General Electronic Configuration
I alkali metals nS
1
IIalkaline earth metals nS
2

2. Occurrence
Element
Relative
abundance
Abundance in
earth’s crust
Li 35 0.0018
Na 7 2.27
K 8 1.84
Rb 23 0.0078
Cs 46 0.00026
•Spodumene -lithium aluminium silicate mineral
(LiAl(SiO
3)
2)
•Rock Salt- sodium chloride(NaCl)
•Trona- hydrated sodium bicarbonate
(NaHCO
3·2H
2O)
•Saltpetre- sodium nitrate(NaNO
3)
•Sylvite- potassium chloride (KCl),
•Carnallite- potassium and magnesium chloride
(KCl.MgCl2.6H
2O)
•Potash (K
2O)
The Rb and Cs are extracted along with Li as there is no convenient or of these alkali metals
Groups I- Alkali Metals

3. Occurrence
Element
Relative
abundance
Be 51
Mg 5
Ca 6
Sr 15
Ba 14
•Beryl (Be₃Al₂SiO₆)
•Phenacite and silicate mineral (Be₂SiO₄)
•Dolomite- (MgCO
3·CaCO
3.2H
2O)
•Calcite- CaCO
3
•Epsomite- MgSO
4
•Carnallite- potassium and magnesium chloride
(KCl.MgCl
2.6H
2O)
•Fluorapatite (Ca
3(PO
4)2.CaF
2
•Celestite SrSO
4
•Strontianite SrCO
3
•Barytes SrSO
4
1911 Nobel Prize in Chemistry for her contributions to the field, including the discovery of radium and
polonium, the isolation of radium, and the study of radium compounds
Groups II- Alkaline Earth Metals

4. Li-Extraction
•Spodumene (LiAl(SiO
3)
2) is first converted to LiCl and then electrolyzed to produce
lithium metal.
•Spondumene is first heated to 1100 °C, then washed with sulphuric acid at 250 °C, and
then water leached. Further, it is treated with washing soda(Li
2CO
3 is insol), followed by
reacting with HCl.
•Alternatively, ore is heated with CaCO
3 and treated with HCl.
Li
Li ore
Fused
ore
Li
2SO
4 Li
2CO
3 LiCl
Li
(cathode)
1100 °C
H
2SO
4,
250 °C,
Water Na
2CO
3 HCl Electrolysis

5. Be-Extraction
Beryl
Fused
ore
BeF
2 Be(OH)
2
Be
Roasting
700 °C
Water
(leaching) pH-12
Mg, 1300 °C

+Na
2SiF
6
•Beryllium is extracted from beryl (Be₃Al₂SiO₆) by roasting the mineral with sodium
silicon fluorides (Na
2SiF
6) at 700-750 and then leaching soluble fluorides with
water. Then, precipitating Be(OH)
2 at about pH 12.
•The metal is usually prepared by the reduction of BeF
2 with Mg at about 1300 °C.
•Be metal is also extracted by electrolysis of fused BeCl
2.

6. Atomic size
Element Li Be B
Atomic radii 157 112 88
Ionic radii (M
+/M
2+
/M
3+
)59(4)
76(6)
27(4)
45(6)
11(4)
Element Na Mg Al
Atomic radii 191 160 143
Ionic radii (M
+/M
2+
/M
3+
)99(4)
102(6)
49(4)
72(6)
39(4)
53(6)
*pm
#(coordination number)
•Atomic Size increases down the group due to
additional shells.
•Cations are smaller than their neutral atoms.
•Group 1 (M⁺) > Group 2 (M²⁺) in ionic radius
Higher coordination numbers in ionic compounds lead to larger ionic radii because the increased number of surrounding
ions allows the central ion's electron cloud to expand, resulting in a larger overall size

7. Ionization Potential (IE)
Element Li Be B
First ionisation energy512 899 801
Second ionisation energy729717572426
Third ionisation energy11809148443660
Element Na Mg Al
First ionisation energy495 737 577
Second ionisation energy456214761816
Third ionisation energy69111484422744
*kJ mol
-1
•Decreases down the group due to increasing atomic size
•Group 1 has lower IE than Group 2 due to single valence
electron
•Low IE makes them highly reactive
E
N
E
R
G
Y
M
(g)
M
+
(g)

8. Group 1:
•Li (Crimson red ) -670 nm
•Na (Yellow) -589 nm
•K (Lilac) -766 nm
•Rb (Reddish-violet) -780 nm
•Cs (Blue) -485 nm
Group 2:
•Be (No color)
•Mg (No color)
•Ca (Brick red) -622nm
•Sr (Crimson) -689 nm
•Ba (Green) -554 nm
Flame colour
Strontium salt
The Thermal excitation of outermost electrons by
the heat of the flame is followed by the emission
of light as the electrons return to their ground
state—this emission of light in the visible region
results in the characteristic colors observed in the
flame.

9. •Group 1: Highly soluble in water, forms hydrated ions
•Group 2: Solubility decreases down the group (BaSO₄ is insoluble)
Hydration enthalpy decreases down the group
Solubility & Hydration
MX
ΔH
solvation
(S) M
+
X
-
(aq)
+
(aq)
ΔH
hydration
M
+
X
-
(aq)
+
(aq)
M
+
X
-
(g)
+
(g)

10. Group 1:
Very reactive with water & oxygen
-forms hydroxides & oxides
Group 2:
Less reactive than Group 1,
-forms oxides & hydroxides
Reactivity

11. Lithium (Li)
•Harder & less reactive than other alkali metals
•Forms covalent compounds (LiCl)
•High polarization power (Fajan’s Rule)
Anomalous Behavior of Li & Be
Beryllium (Be)
•Forms covalent compounds
•High ionization energy
•Does not react with water

12. •Form covalent compounds
•Have similar melting points &
solubility
•Show amphoteric behavior
(Be(OH)₂, Al(OH)₃)
Why do diagonal relationships occur?
It arises mainly due to
•Similar atomic/ionic size
•Similar electronegativity/Ionization potential
•Similar charge density (polarizing power)
Diagonal Relationship (Li-Mg, Be-Al)
Anomalous Behavior of Li & Be

13. Property Lithium (Li) Magnesium (Mg)
Atomic radius ~157 pm ~160 pm
Electronegativity1.0 1.2
Ion size (M⁺) Li⁺ ~76 pm Mg²⁺ ~72 pm
Solubility of
compounds
Li₂CO₃ and MgCO₃ decompose on heating
Hydroxides LiOH and Mg(OH)₂ are sparingly soluble
Nitrides Both form stable nitrides (Li₃N, Mg₃N₂)
Li Mg: Diagonal Relationship

14. Property Beryllium (Be) Aluminium (Al)
Electronegativity1.5 1.5
Ion size (M²⁺/M³⁺)Be²⁺ ~45 pm Al³⁺ ~53 pm
Amphoteric oxidesBeO is amphotericAl₂O₃ is amphoteric
Coordination tendency
Forms covalent
compounds (e.g.,
BeCl₂)
AlCl₃ is covalent in
vapor phase
Complex formationBe forms [BeF₄]²⁻Al forms [AlF₆]³⁻
Be Al: Diagonal Relationship

15. •Na⁺ & K⁺: Essential for nerve impulses, muscle contraction, and Osmotic
balance
•Mg²⁺: Present in chlorophyll
•Ca²⁺: Muscle contraction, Structural component in bones & teeth
Ca
10(PO
4)
6(OH)
2.
Biological role
hydroxyapatite