Learn Unit 10-s -Block Elements (Alkali and Alkaline Earth Metals) with Free Lessons & Tips

• Physical and Chemical Features of Alkali Metals:

  • Physical: Alkali metals are soft, shiny, silvery-white metals with low densities. They have low melting and boiling points compared to other metals.
  • Chemical: Alkali metals are highly reactive, especially with water and oxygen. They readily form ionic compounds with nonmetals, and their reactivity increases down the group.

• Characteristics of Alkaline Earth Metals:

  • Alkaline earth metals are reactive metals but less so than alkali metals.
  • They have higher melting and boiling points compared to alkali metals.
  • They form divalent cations (2+ ions) in compounds.
  • They are less reactive with water than alkali metals but still react vigorously with acids.
  • They have relatively low electronegativities and ionization energies compared to transition metals.

• Absence of Alkali Metals in Nature: Alkali metals are highly reactive and readily react with moisture and oxygen in the atmosphere, making them unstable in their pure form. They are typically found in nature as compounds rather than as pure metals.

Oxidation State of Sodium in Na2O2: In Na2O2Na2O2, each oxygen atom is in the peroxide ion (O22−O22−). Since the overall charge of the compound is 0, sodium must be in the +1 oxidation state to balance the negative charges from the peroxide ions. So, the oxidation state of sodium in Na2O2Na2O2 is +1.

• Reactivity of Sodium vs. Potassium: Sodium is less reactive than potassium because sodium has a larger atomic radius and higher ionization energy compared to potassium. These factors make it more difficult for sodium to lose an electron and react with other substances compared to potassium.

• Comparison of Alkali Metals and Alkaline Earth Metals:

  • Ionization Enthalpy: Alkali metals have lower ionization enthalpies than alkaline earth metals due to their larger atomic size and lower effective nuclear charge.
  • Basicity of Oxides: Alkali metal oxides are more basic than alkaline earth metal oxides because alkali metals form hydroxides that are more soluble in water, leading to stronger alkaline solutions.
  • Solubility of Hydroxides: Alkali metal hydroxides are more soluble in water compared to alkaline earth metal hydroxides due to smaller lattice energies and higher hydration energies of alkali metal ions.

• Similarities between Lithium and Magnesium: Both lithium and magnesium are relatively hard metals with low densities. They have high melting and boiling points compared to other alkali metals and alkaline earth metals, respectively. They also form covalent compounds (e.g., organolithium and organomagnesium compounds) in addition to ionic compounds.

• Obtaining Alkali and Alkaline Earth Metals by Chemical Reduction: Alkali and alkaline earth metals cannot be obtained by chemical reduction methods because they are highly reactive and readily form positive ions. Even in their ore forms, they exist as ionic compounds and cannot be reduced directly by chemical means. Instead, these metals are typically obtained through electrolytic processes or by reaction with other metals in certain conditions.