🧶Inorganic Chemistry I Unit 4 – Main Group Elements – s–Block

Key Concepts and Definitions

• s-Block elements located in groups 1 (alkali metals) and 2 (alkaline earth metals) of the periodic table
• Valence electrons in the outermost s orbital, resulting in similar chemical properties within each group
• Alkali metals have one valence electron (ns1), while alkaline earth metals have two (ns2)
• Electropositive nature due to low ionization energies and strong tendency to lose valence electrons
• Form ionic compounds with non-metals, typically with a +1 oxidation state for alkali metals and +2 for alkaline earth metals
• Metallic character increases down the group as atomic size increases and ionization energy decreases
• Reactivity increases down the group due to lower ionization energies and more easily lost valence electrons

Electronic Configuration and Periodic Trends

• General electronic configuration: [Noble gas] ns1 for alkali metals and [Noble gas] ns2 for alkaline earth metals
• Atomic and ionic radii increase down the group due to the addition of electron shells
• Ionization energy decreases down the group as valence electrons become more distant from the nucleus and experience greater shielding
• Electronegativity decreases down the group, making the elements more electropositive
• Metallic character increases down the group, with elements becoming softer and having lower melting and boiling points
• Reactivity increases down the group, with elements more readily losing valence electrons and forming ionic compounds
  • Francium (Fr) and Radium (Ra) are radioactive and have limited chemical data due to their short half-lives

Properties of s-Block Elements

• Soft, silvery-white metals with low densities (lithium, sodium, and potassium can float on water)
• Low melting and boiling points compared to other metals, decreasing down the group
• High thermal and electrical conductivity due to the presence of delocalized electrons
• Ductile and malleable, easily cut with a knife (except beryllium)
• Highly reactive, readily losing valence electrons to form stable cations
  • Reactivity increases down the group, with francium being the most reactive alkali metal
• Form basic oxides and hydroxides when reacting with oxygen and water, respectively
• Alkaline earth metals are harder and denser than alkali metals due to their higher atomic mass and smaller atomic radii

Reactions and Compounds of Alkali Metals

• React vigorously with water to produce hydrogen gas and metal hydroxides (LiOH, NaOH, KOH)
  • Reactivity increases down the group: 2M(s) + 2H2O(l) → 2MOH(aq) + H2(g)
• React with halogens to form ionic halides (LiF, NaCl, KBr)
  • M(s) + X2(g) → MX(s), where X = F, Cl, Br, I
• React with oxygen to form various oxides (Li2O, Na2O, K2O)
  • 4M(s) + O2(g) → 2M2O(s)
• Form soluble salts with strong acids (HCl, H2SO4, HNO3)
  • M(s) + HCl(aq) → MCl(aq) + 1/2H2(g)
• Reducing agents in organic synthesis, such as the Birch reduction using lithium or sodium in liquid ammonia

Reactions and Compounds of Alkaline Earth Metals

• Less reactive with water compared to alkali metals, forming metal hydroxides and hydrogen gas
  • M(s) + 2H2O(l) → M(OH)2(aq) + H2(g)
• React with halogens to form ionic halides (MgCl2, CaCl2, SrBr2)
  • M(s) + X2(g) → MX2(s), where X = F, Cl, Br, I
• Form basic oxides (MgO, CaO, SrO) when heated in oxygen
  • 2M(s) + O2(g) → 2MO(s)
• Produce insoluble carbonates (MgCO3, CaCO3) and sulfates (MgSO4, CaSO4) in aqueous solutions
  • M(OH)2(aq) + CO2(g) → MCO3(s) + H2O(l)
• Act as Lewis acids, forming complexes with ligands such as EDTA (ethylenediaminetetraacetic acid)
  • Ca2+(aq) + EDTA4-(aq) → [Ca(EDTA)]2-(aq)

Industrial and Biological Significance

• Sodium chloride (NaCl) is an essential electrolyte for biological processes and is used in food preservation and deicing roads
• Potassium compounds (KCl, K2SO4) are used as fertilizers in agriculture
• Lithium compounds (Li2CO3, LiOH) are used in the production of ceramics, glass, and lithium-ion batteries
• Magnesium alloys (with aluminum) are lightweight materials used in aerospace and automotive industries
• Calcium compounds (CaO, Ca(OH)2) are used in construction materials (cement, mortar) and as pH regulators in water treatment
• Strontium compounds (SrCO3, SrCl2) are used in fireworks and dental applications
• Barium sulfate (BaSO4) is used as a contrast agent in medical X-rays due to its high atomic mass and low solubility
• Calcium and magnesium ions are essential for biological processes, such as muscle contraction, nerve impulse transmission, and blood clotting

Analytical Techniques and Applications

• Flame tests used to identify alkali and alkaline earth metals based on characteristic flame colors (Li: red, Na: yellow, K: violet, Ca: orange, Sr: red, Ba: green)
• Atomic absorption spectroscopy (AAS) used to quantify the concentration of metal ions in solution
• Complexometric titrations with EDTA to determine the concentration of alkaline earth metal ions in water hardness analysis
• Ion-exchange chromatography to separate and purify metal ions based on their affinity for the stationary phase
• Gravimetric analysis of sulfate and carbonate salts to determine the concentration of alkaline earth metals in samples
• Qualitative analysis of group 1 and 2 cations using selective precipitation and solubility rules
  • Sodium hydroxide (NaOH) used to precipitate magnesium and calcium ions as hydroxides
  • Ammonium carbonate ((NH4)2CO3) used to precipitate strontium and barium ions as carbonates

Practice Problems and Review

• Write balanced chemical equations for the reactions of alkali and alkaline earth metals with water, halogens, and oxygen
• Predict the products and solubility of compounds formed by the reaction of s-block elements with common anions (OH-, CO32-, SO42-, Cl-)
• Compare the reactivity, atomic and ionic radii, ionization energy, and electronegativity of s-block elements based on their position in the periodic table
• Calculate the concentration of metal ions in solution using data from analytical techniques such as AAS or complexometric titrations
• Explain the industrial and biological applications of s-block elements and their compounds
• Identify unknown s-block elements based on their flame test colors and selective precipitation reactions
• Discuss the trends in physical and chemical properties of s-block elements and relate them to their electronic configuration and periodic position
• Solve stoichiometry problems involving the reactions of s-block elements with acids, bases, and other common reagents