Group 1 Elements

Session 1: Group 1 Elements

  • Alkali metals (Group 1): Li, Na, K, Rb, Cs, and Fr.
  • They are called "alkali metals".
  • Hydrogen is placed above Li in some periodic tables.
  • Alkali metals are reactive and not found as free metals.
  • Na is present as NaCl in underground deposits and seawater.
  • K salts are found in seawater and as carnalite (KCl·MgCl2 ·6H2O) or potash (KOH).
  • Na and Li are obtained by electrolysis of their molten chlorides: 2NaCl(l)→2Na(s)+Cl2(g)2 NaCl(l) \rightarrow 2 Na(s) + Cl_2(g)
  • K is made by the reaction of Na vapour with molten KCl at 850 °C: Na(vapour)+KCl(l)→NaCl(l)+K(l)Na(vapour) + KCl(l) \rightarrow NaCl(l) + K(l)
  • Rb and Cs are made by reduction of their chlorides with Ca metal at 800 °C: Ca(l)+2RbCl(l)→CaCl2(l)+2Rb(l)Ca(l) + 2 RbCl(l) \rightarrow CaCl_2(l) + 2 Rb(l)
  • All Fr isotopes are radioactive.
  • Group 1 elements are soft metals that conduct electricity and heat.
  • Ionic radius, r(M+), increases down the group.
  • Melting point decreases from Li to Cs.
  • Li, Na, and K have densities (d) less than water and float on water.
  • Valence electron configuration: ns1. Tendency to lose the single s-electron to attain noble gas configuration: M→M++e−M \rightarrow M^+ + e^-
  • They all form only M+ ions due to the very high second ionization energies (IE2).
  • Group 1 elements form colorless ionic salts with common simple anions, and the oxidation state is always +1.
  • Almost all alkali metal derivatives are ionic except some Li compounds.
  • Simple salts of alkali metals are very soluble in water, but LiF and Li2CO3 are partially soluble.
  • Alkali metals are stored in dry hydrocarbon solvents (paraffin oil) to prevent reaction with atmospheric oxygen or moisture.
  • Combustion products in oxygen vary; different oxygen-containing anions (oxide, peroxide, superoxide) are formed.
  • Hydrolysis of lithium monoxide gives LiOH.
  • Hydrolysis of sodium peroxide at 0 °C gives NaOH and H2O2.
  • Hydroxides, H2O2, and O2 are produced when superoxides of K, Rb, and Cs are hydrolyzed.
  • Lithium forms only the monoxide.
  • Superoxide of sodium is unstable.
  • Superoxide becomes more stable down the group.
  • Large alkali metals form stable superoxides MO2MO_2 (M = K, Rb, Cs), which are ionic and paramagnetic.
  • The peroxides (M2O2) have ionic structures and react with cold water to give H2O2.
  • Alkali metal peroxides are powerful oxidizing agents and oxidize sulfides to sulfates.
  • 2M(s)+2H<em>2O(l)→2MOH(aq)+H</em>2(g)2 M(s) + 2H<em>2O(l) \rightarrow 2 MOH(aq) + H</em>2(g)
  • Non-metals (C, N, and O) do not react with aqueous NaOH, but many other elements do.
  • LiCl, LiBr, and LiI have some covalent character and are more soluble in alcohol.
  • The covalent character of lithium compounds is due to the strong polarizing power of the Li+ ion.

Essential Points

  • s-block elements: soft, reactive metals with low melting points, low densities, low first ionization energies, high second ionization energies, and very negative standard reduction potentials.
  • Valence electron configuration: ns1. Readily form M+ ions (strong reducing agents).
  • Na, Li, are obtained by electrolysis of their molten chloride. K is made by reacting molten KCl with sodium vapor.
  • They form three types of oxides: monoxide, peroxide, and superoxide.
  • Alkali metal hydroxides are used in acid-base titrations.