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

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

• 1.
  S-block Elements K Ca RbSr Cs Ba Fr Ra Li Be Na Mg H IA IIA 1 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 nS1 II alkaline earth metals nS2
• 2.
  Occurrence Element Relative abundance Abundance in earth’s crust Li35 0.0018 Na 7 2.27 K 8 1.84 Rb 23 0.0078 Cs 46 0.00026 • Spodumene -lithium aluminium silicate mineral (LiAl(SiO3)2) • Rock Salt- sodium chloride(NaCl) • Trona- hydrated sodium bicarbonate (NaHCO3·2H2O) • Saltpetre- sodium nitrate(NaNO3) • Sylvite- potassium chloride (KCl), • Carnallite- potassium and magnesium chloride (KCl.MgCl2.6H2O) • Potash (K2O) 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 Ca6 Sr 15 Ba 14 • Beryl (Be₃Al₂SiO₆) • Phenacite and silicate mineral (Be₂SiO₄) • Dolomite- (MgCO3·CaCO3.2H2O) • Calcite- CaCO3 • Epsomite- MgSO4 • Carnallite- potassium and magnesium chloride (KCl.MgCl2.6H2O) • Fluorapatite (Ca3(PO4)2.CaF2 • Celestite SrSO4 • Strontianite SrCO3 • Barytes SrSO4 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(SiO3)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(Li2CO3 is insol), followed by reacting with HCl. • Alternatively, ore is heated with CaCO3 and treated with HCl. Li Li ore Fused ore Li2SO4 Li2CO3 LiCl Li (cathode) 1100 °C H2SO4, 250 °C, Water Na2CO3 HCl Electrolysis
• 5.
  Be-Extraction Beryl Fused ore BeF2 Be(OH)2 Be Roasting 700 °C Water (leaching)pH-12 Mg, 1300 °C +Na2SiF6 • Beryllium is extracted from beryl (Be₃Al₂SiO₆) by roasting the mineral with sodium silicon fluorides (Na2SiF6) 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 BeF2 with Mg at about 1300 °C. • Be metal is also extracted by electrolysis of fused BeCl2.
• 6.
  Atomic size Element LiBe B Atomic radii 157 112 88 Ionic radii (M+/M2+/M3+) 59(4) 76(6) 27(4) 45(6) 11(4) Element Na Mg Al Atomic radii 191 160 143 Ionic radii (M+/M2+/M3+) 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) ElementLi Be B First ionisation energy 512 899 801 Second ionisation energy 7297 1757 2426 Third ionisation energy 11809 14844 3660 Element Na Mg Al First ionisation energy 495 737 577 Second ionisation energy 4562 1476 1816 Third ionisation energy 6911 14844 22744 *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: Highlysoluble in water, forms hydrated ions •Group 2: Solubility decreases down the group (BaSO₄ is insoluble) Hydration enthalpy decreases down the group Solubility & Hydration M X ΔHsolvation (S) M+ X- (aq) + (aq) ΔHhydration M+ X- (aq) + (aq) M+ X- (g) + (g)
• 10.
  Group 1: Very reactivewith 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 covalentcompounds • 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 Electronegativity 1.0 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) Electronegativity 1.5 1.5 Ion size (M²⁺/M³⁺) Be²⁺ ~45 pm Al³⁺ ~53 pm Amphoteric oxides BeO is amphoteric Al₂O₃ is amphoteric Coordination tendency Forms covalent compounds (e.g., BeCl₂) AlCl₃ is covalent in vapor phase Complex formation Be 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 Ca10(PO4)6(OH)2. Biological role hydroxyapatite