Inorganic Chemistry - Representative Elements PDF

Inorganic Chemistry Representative Elements Lecture 6 Group 2 (IIA) alkaline earth metals Dr. Abbas Mamdoh Abbas Group 2: The Alkaline Earth Metals Beryllium, Magnesium, Calcium, Strontium, Barium, and Radium The Alkaline Earth Metals General...

Inorganic Chemistry Representative Elements Lecture 6 Group 2 (IIA) alkaline earth metals Dr. Abbas Mamdoh Abbas Group 2: The Alkaline Earth Metals Beryllium, Magnesium, Calcium, Strontium, Barium, and Radium The Alkaline Earth Metals General properties  The Alkaline Earth Metals General characteristics Electronic configuration Physical appearance Metallic (Electropositive) character. Atomic radius(Ionic radius) Electronegativity Density Melting and Boiling points Oxidation state Nature of Bonding Hydration energy and Ionic mobilities Electrode potentials Ionization enthalpy  The Alkaline Earth Metals Principles of extraction  Electrolytic Reduction The alkaline earth metals are prepared by the electrolysis of their fused anhydrous salts containing alkali metal salts.  Thermal Reduction BeF2+Mg→Be+MgF2 3CaO + 2Al → 3 Ca + Al2O3 + heat BaO + C → Ba + CO (not recommended)  The Alkaline Earth Metals Chemical Properties G2 elements are less electropositive than those in G1 React with water (except Be) to form H2 and metal hydroxides. Be(OH)2 is amphoteric while other hydroxides are basic. The basic character of the hydroxides increases down the group due to decrease of ionization energy and lattice energy. These hydroxides are less soluble in water than the corresponding alkali metal hydroxides. The solubility increases down the group due to rapid decrease in lattice energy.  The Alkaline Earth Metals Chemical Properties Elements burn in O2 to form oxides (MO), also by the thermal decomposition of oxysalts (MCO3). All oxides are ionic, and basic and react with water (except BeO covalent, and amphoteric, and do not react with water). From BeO to BaO ionic nature, solubility and basic nature increase while lattice energy and stability decrease. Only Ba and Sr form peroxide (MO2). All are white solid ionic compounds  The Alkaline Earth Metals Chemical Properties All halides formed by direct reaction of metal with halogen under high temperature or by the reaction of HX with MO, M(OH)2 or MCO3. Halides are ionic, hygroscopic, high melting and form hydrates. BeX2 < MgX2 < CaX2 < SrX2 < BaX2 (ionic and solubility) MF2 is insoluble. BeCl2 is covalent polymeric with low melting point (volatile solid). BeCl2 have three forms: vapor (as monomer and dimer) and solid as  Cl Cl Be Be Cl Cl Be Cl Cl Monomer Dimer Bridge bond 3-center bond Cl Cl Cl Be Be Be Be Cl Cl Cl banana bond Polymer  The Alkaline Earth Metals Chemical Properties All hydrides are reducing agents, react with H2O and liberate H2. Be and Mg gave covalent hydride with polymeric structure Ca, Ba and Sr gave ionic hydride. (BeH2)n has the structure 3-cente H H H Be Be Be Be H H H banana  The Alkaline Earth Metals Chemical Properties The thermal decomposition of the CO32- of the G2 elements as follow: Ba > Sr > Ca > Mg > Be (1360, 1290, 900, 540, and lower 100, respectively)? The thermal decomposition of the SO42- of the G2 elements as follow: Sr > Ca > Mg > Be (1374, 1149, 895, and 580, respectively)?  The Alkaline Earth Metals Chemical Properties Complex formation Solubility in liquid ammonia [M(NH3)6]2+ (s) → M(NH2)2(s) + 4NH3(g) + H2(g) Ammoniate amide Action of Acids Action of Bases  The Alkaline Earth Metals Chemical Properties Anomalous Behavior of Beryllium: Beryllium differs from the rest of the group as it has extremely small size and comparatively high electronegativity and ionization energy, so it form covalent bonds. Oxide and hydroxides of beryllium are amphoteric while those of other metals are basic in character. Compounds of beryllium dissolve in organic solvents and hydrolyze in water while compounds of other alkaline earth metals do not.  The Alkaline Earth Metals Chemical Properties Anomalous Behavior of Beryllium: Beryllium can not react with water even at very high temperatures while other alkaline earth metals do react with water. Beryllium does not liberate hydrogen from acids, but other metals do so. Hydride and halides of beryllium are covalent and polymeric while those of other metals do not exist in polymeric form and are ionic (except Mg). Beryllium does not combine directly with hydrogen while other elements do.  The Alkaline Earth Metals Chemical Properties Diagonal Relationship between Beryllium and Aluminum. Both metals have a strong tendency to form covalent compounds, soluble in organic solvents. Both metals render passive on treatment with concentrated nitric acid due to the formation of a protective covering on their surface, by their oxides. Both metals react with sodium hydroxide to form soluble complexes Be + NaOH → Na2BeO2 + H2 2Al + 2NaOH + 2H2O → 2 NaAlO2 + 3H2  The Alkaline Earth Metals Chemical Properties Diagonal Relationship between Beryllium and Aluminum. The oxides and hydroxides of both metals are amphoteric. Chlorides of both metals are electron deficient and act as strong Lewis acids. Both metals show tendency to form complexes such as [BeF 6]2− and [AlF6]3−. Carbides of both the metals evolve methane on treatment with water. Be2C + 2H2O → 2BeO + CH4 No. Properties Effect No. Properties Effect 1 Atomic number increase 11 Complex formation decrease 2 Atomic radius increase 12 Hydration decrease 3 Ionic radius increase 13 Cond. Of M+ in H2O increase 4 Metallic increase 14 First ionization decrease 5 Thermal cond. Increase potential 6 Electrical cond. Increase 15 Stability of M in air decrease 7 Reaction of M with H2O increase 16 Bsicity of M(OH)2 increase 8 Hardness decrease 17 Electronegativity decrease 9 Melting point decrease 18 Electron affinity decrease 10 Ease of thermal decrease 19 Ionic character increase decomposition of its 20 Softness increase compounds 21 Cohesive force decrease Thanks