Jaron Mason

 All group 1A elements have 1 valence electron.  All group 1A elements, except hydrogen, are extremely active metals (H acts as a non- metal).  The 1A metals are referred to as Alkali metals The Group 1A Elements

Sources and properties TABLE 19.3 Sources and Methods of Preparation of the Pure Alkali Metals ElementSourceMethod of Preparation LithiumSilicate minerals such as spodumene, LiAl(Si 2 O 6 ) Electrolysis of molten LiCl SodiumNaClElectrolysis of molten NaCl PotassiumKClElectrolysis of molten KCl RubidiumImpurity in lepidolite, Li 2 (F,OH) 2 Al 2 (SiO 3 ) 3 Reduction of RbOH with Mg and H 2 CesiumPollucite (Cs 4 Al 4 Si 9 O 26 ∙H 2 O) and impurity in lepidolite Reduction of CsOH with Mg and H 2 TABLE 19.4 Selected Physical Properties of the Alkali Metals ElementIonization Energy (kJ/mol) Standard reduction potential (V) Radius of M + (pm) Melting point (C) Lithium Sodium Potassium Rubidium Cesium

Reaction with water  Alkali metals react vigorously with water: 2M(s)+2H 2 O(l)→2M + (aq)+2OH - (aq)+H 2 (g)  Based on ionization energies, lithium would be expected to be the weakest reducing agent in water, but its standard reduction potential suggests it is the strongest. Lithium has a high energy of hydration, so the high charge density attracts more water molecules.  Lithium reacts more slowly with water than other Alkali metals, because the high melting point prevents the reaction from melting the lithium, increasing surface area.

Oxides, peroxides, and superoxides  Lithium is the only Alkali metal that forms a normal oxide with excess oxygen: 4Li(s) + 1O 2 (g) → 2Li 2 O(s)  Sodium will only form Na 2 O when there is limited oxygen. In excess oxygen, it forms sodium peroxide: 4Na(s) + 2O 2 (g) → 2Na 2 O 2 (s)  Potassium, rubidium, and cesium react with oxygen to form superoxides, which contain O 2 - : K(s) + O 2 (g) → KO 2 (s)  Superoxides react with water or carbon dioxide to release oxygen gas: 2KO 2 (s) + 2H 2 O → 2K + (aq) + 2OH - (aq) + O 2 (g) + H 2 O 2 4KO 2 (s) + 2CO 2 → 2K 2 CO 3 (s) + 3O 2 (g)

Predicting Reaction Products  Predict the products formed by the following reactants: A. Li 3 N(s) and H 2 O(l) B. KO 2 (s) and H 2 O(l)  Solution: A. Li 3 N(s) + H 2 O(l) → NH 3 (g) + 3Li + + 3OH - B. KO 2 (s) + H 2 O(l) → 2K + (aq) + 2OH -

19.3 Hydrogen  Under normal conditions, hydrogen is colorless and odorless.  It is non-polar and has a low molar mass, so the boiling point (-253C) and melting point (-260C) are extremely low.  Hydrogen is extremely flammable and mixtures of hydrogen in air with 18-60% H are considered explosive.

Sources and Uses  A major source of hydrogen is the reaction of methane with water at high temperatures and pressures with a catalyst: CH 4 (g) + H 2 O(g) → CO(g) + 3H 2 (g)  Hydrogen is also formed in large quantities in the production of gasoline when large hydrocarbons are broken down (cracked) into smaller molecules.  A major industrial use for hydrogen is the production of ammonia through the Haber process.  Hydrogen is also used to create shortening by hydrogenating vegetable oils. CC HH CC HH HH +H 2

Hybrides  Hydrogen behaves as a nonmetal, forming covalent compounds with other non-metals and salts with very active metals.  There are three types of binary compounds containing hydrogen known as hybrides: Ionic hybrides Covalent hybrides Metallic hybrides

Ionic hybrides  Ionic (salt-like) hybrides are formed when hydrogen combines with metals from groups 1A and 2A.  LiH and CaH 2 are examples of ionic hybrides and contain hydride (H - ) ions.  Hydride ions are a string reducing agent because of the weak 1+ charge and the strong electron-electron repulsion.  There is a violent reaction between hybrides and water, resulting in the formation of hydrogen gas: LiH(s) + H 2 O(l) → H 2 (g) + Li + (aq) + OH - (aq)

Covalent hybrides  Covalent hybrides form when hydrogen reacts with on-metals.  Examples are HCl, CH 4, NH 3, and H 2 O.  Water is considered the most important covalent hybride. It has a high heat of vaporization for its molar mass and a large heat capacity, making it a useful coolant. Water is an excellent solvent for ionic and polar materials because of hydrogen bonding, so it provides an effective medium for biological processes.

Metallic (interstitial) hybrides  Metallic hybrides are formed when crystals of transition metals absorb hydrogen gas.  The small hydrogen molecules dissociate at the metal’s surface and migrate into the crystal structure.  The metal-hydrogen mixtures are better considered solid solutions than actual compounds.  Hydrogen can be separated from other gasses by allowing it to diffuse through a metal barrier into a separate area.  Hydrogen can react with transition metals, but metallic hybrides tend to have variable compositions.  These nonstoichiometric hybrides have formulas such as LaH 2.76 and VH 0.56 dependent on how much hydrogen is absorbed.  Absorbed hydrogen can be released by heating the metal hybride.