Alkali and Alkaline Earth Metals

Alkali and Alkaline Earth Metals: Characteristics

• Alkali metals belong to Group I [IA].
• Alkaline earth metals belong to Group II [IIA].
• Alkali metals possess low density.
• Alkaline earth metals possess higher density.
• Alkali metals possess a low melting point.
• Alkaline earth metals possess a higher melting point.
• Alkali metals possess a low boiling point.
• Alkaline earth metals possess a higher boiling point.
• Alkali metals exhibit a characteristic color in the flame test.
• Magnesium (Mg) and Beryllium (Be) do not give a characteristic color.
• Alkali metals have a strongly electropositive character.
• Alkaline earth metals have a less electropositive nature.
• Alkali metals are highly reactive.
• Alkaline earth metals are less reactive.
• Alkali metals react with air.
• Alkaline earth metals tarnish slowly forming an oxide layer when exposed to moist air.
• Alkali metals react with water, shown as: 2M + 2H2O → 2MOH + H2.
• Alkaline earth metals react with water, shown as: M + 2H2O→M(OH)2 + H2.
• Alkali metals react with acids, shown as: M + 2HCl →MCl2 + H2.
• Alkaline earth metals react with acids, shown as: M + H2SO4→MSO4 + H2.

Physical Properties: Metals vs. Non-metals

• Metals are generally hard solids and vaporize at high temperatures.
• Non-metals are generally soft, and often gases or liquids.
• Metals have a metallic luster, and can be polished.
• Non-metals lack luster.
• Metals generally have high melting and boiling points, excluding alkali metals and mercury (Hg).
• Non-metals usually have low melting and boiling points.
• Metals generally have high density, excluding alkali metals like sodium (Na) and potassium (K).
• Non-metals generally have low density.
• Metals are generally malleable and ductile, possessing high tensile strength.
• Non-metals are non-malleable and non-ductile.
• Metals form alloys and amalgams (Bronze, Sodium amalgam).
• Non-metals do not form alloys.
• Metals are hard, but not brittle.
• Non-metals are brittle in nature.
• Metals are generally good conductors of heat and electricity.
• Non-metals are poor conductors of heat and electricity.
• Metals generally do not dissolve in liquids, except via chemical reactions.
• Non-metals are generally soluble in water or other solvents and do not react chemically.

Chemical Properties: Metals vs. Non-metals

• Metals have 1, 2, or 3 valence electrons in their electronic configurations.
• Non-metals have 4, 5, 6, or 7 valence electrons in their electronic configurations.
• Metals are electropositive, readily losing electrons to form positively charged ions (cations).
• Non-metals are electronegative, readily gaining electrons to form negatively charged ions (anions).
• Metals losing electrons during chemical reactions make them good reducing agents.
• Non-metals easily gain electrons, which makes them good oxidizing agents.
• Metal oxides may be basic and dissolve in water to form alkaline solutions.
• Non-metal oxides generally form acidic oxides and dissolve in water to form acidic solutions.
• Metals do not usually react with hydrogen (H2).
• Non-metals do not react with dilute acids to liberate hydrogen.
• Metals react with dilute hydrochloric acid (HCl) and dilute sulfuric acid (H2SO4 to liberate hydrogen gas (H2) if they are above hydrogen in the activity series.
• Metals readily react with chlorine (Cl2) to form chlorides.
• Non-metals usually form chlorides, which are volatile covalent liquids or gases.
• Metals form electrovalent or ionic compounds that conduct electricity in the fused state or in solution due to free electrons or ions (e.g., NaCl, CaCl2, MgCl2).
• Non-metals form covalent compounds that do not conduct electricity because there are no free electrons or ions to carry current.
• Electrolysis of molten calcium chloride (CaCl2) liberates calcium metal at the cathode and chlorine gas at the anode.

Activity Series of Metals

• Metals vary in their tendency to give up valence electrons.
• Metals are arranged in a series based on their decreasing reactivity.
• Metals at the series' top are easily oxidized and strongly electropositive.
• Metals at the top can displace metals below them from their salt solutions.

Characteristics of Metallic Compounds

• Oxides, Hydroxides, Carbonates and Nitrates vary for different metals.
• Potassium (K) and Sodium (Na) Oxides are stable to heat and soluble in water.
• Potassium (K) and Sodium (Na) Hydroxides are stable to heat and soluble in water.
• Potassium (K) and Sodium (Na) Carbonates are stable to heat and soluble in water.
• Potassium (K) and Sodium (Na) Nitrates decompose to give nitrite and oxygen when heated.
• Calcium (Ca) to Copper (Cu) Oxides are stable to heat.
• Calcium (Ca) to Copper (Cu) Hydroxides decompose to give metal oxide and water.
• Calcium (Ca) to Copper (Cu) Carbonates decompose to give metal oxide and CO2.
• Calcium (Ca) to Copper (Cu) Nitrates decompose to give metal oxide and NO2.
• Mercury (Hg) to Gold (Au) Oxides decompose to give metal and oxygen.
• Mercury (Hg) to Gold (Au) Hydroxides either do not exist or are rarely formed and insoluble in water.
• Mercury (Hg) to Gold (Au) Carbonates decompose to give metal, CO2 and O2 and are insoluble in water.
• Mercury (Hg) to Gold (Au) Nitrates decompose to give metal, NO2 and O2

Corrosion

• Corrosion occurs when a metal's surface is exposed to air, moisture, or other substances.
• Rusting is the corrosion of iron.
• Rusting occurs through the slow oxidation of iron by atmospheric oxygen in the presence of water.
• The chemical equation for rusting is: 4Fe + 3O2 + 2xH2O → 2Fe2O3.xH2O.
• Rusting requires the presence of both water (or moisture) and air (or oxygen).
• Barrier protection is a method of corrosion prevention.
• Barrier protection involves not allowing contact between the metal surface and atmospheric agents like air/water.
• Barrier protection can be achieved by coating the metal with another metal using electroplating.
• Sacrificial protection involves covering the metal to be protected with a more electropositive metal like zinc or magnesium.
• Galvanization is a process where iron is coated with zinc.

Extraction of Metals: Key Terms

• Metallurgy extracts metals in pure form from their ores.
• Minerals are naturally occurring metal compounds mixed with soil, sand, limestone, and rocks.
• Gangue refers to the earthy impurities (silica, mud) alongside the ore.
• Ores are minerals from which metals are commercially extracted with minimal cost and effort.
• Flux removes gangue by combining with it in a furnace.
• Slag is the fusible substance formed when flux reacts with impurities during metal extraction.
• Smelting reduces roasted oxide ore and removes gangue using flux.

Steps in Metal Extraction

• Pulverization is the process of crushing ores into fine powder via jaw crushers and ball mills.
• Gravity separation separates particles based on density on a vibrating, sloped table with water.
• Magnetic separation separates magnetic particles using a conveyor belt and magnetic wheel.
• Froth flotation separates particles by their wettability using oil and air in a tank, mainly for sulphide ores.
• Roasting heats concentrated ore to high temperature with excess air. For example: 2ZnS + 3O2 → 2ZnO + 2SO2
• Calcination involves heating concentrated ore without air at temperatures insufficient to melt it. For example: ZnCO3 → ZnO + CO2
• Electrolytic reduction uses electrolysis to reduce highly electropositive metals (K, Na, Ca, Mg, Al) oxides/halides.
• Aluminium oxide electrolysis forms pure aluminium metal at the cathode and oxygen gas at the anode.
• Reduction uses reducing agents like carbon to reduce metallic oxides. An example reaction is: ZnO + C → Zn + CO.
• Distillation refines volatile metals like zinc and mercury.
• Liquation refines low-melting-point metals like lead and tin.
• Oxidation refines metals by oxidizing impurities.
• Electrolytic refining refines metals via electrolysis.

Common Ores

• Bauxite (Al2O3.2H2O) is a hydrated aluminum oxide.
• Cryolite (Na3AlF6) is sodium aluminum fluoride.
• Corundum (Al2O3) is an anhydrous aluminum oxide.
• Red haematite (Fe2O3) is an anhydrous ferric oxide.
• Brown haematite (2Fe2O3.3H2O) is a hydrated ferric oxide.
• Magnetite (Fe3O4) is triferric tetraoxide.
• Iron pyrites (FeS2) is iron disulphide.
• Siderite (FeCO3) is ferrous carbonate.
• Zinc blende (ZnS) is zinc sulphide.
• Zincite (ZnO) is zinc oxide.
• Calamine (ZnCO3) is zinc carbonate.

Aluminium Extraction (Bayer Process)

• Impure bauxite converts into sodium aluminate when heated with sodium hydroxide (NaOH).
• Sodium aluminate converts to aluminum hydroxide (Al(OH)3).
• Aluminum hydroxide converts to pure alumina upon heating.

Electrolytic Reduction of Aluminium (Hall-Heroult Process)

• Electrolyte composition is 20% molten alumina, 60% cryolite, and 20% fluorspar.
• Electrolytic cell is a rectangular steel tank with carbon lining.
• Cathode is carbon lining, and anode is thick carbon (graphite).
• Temperature is 950°C, current 100 amperes at 6–7 volts.
• Cryolite ionizes into 3Na¹⁺ + Al³⁺ + 6F¹⁻.
• Fluorspar ionizes into Ca²⁺ + 2F¹⁻.
• Alumina ionizes into 2Al³⁺ + 3O²⁻.
• At the cathode, 2Al³⁺ + 6e⁻ becomes 2Al.
• At the anode, 3O²⁻ - 6e⁻ becomes 3[O] then 3O₂.
• Pure aluminium metal forms at the cathode, and oxygen gas at the anode.
• Hoope's process refines aluminium with three layers in a tank.
• The Upper layer is pure molten aluminium with carbon electrodes as the cathode.
• The Middle layer consists of cryolite, BaF2, AlF, and CaF2.
• The Lower layer consists of impure aluminium with carbon lining as the anode.
• Aluminium ions gain electrons to become aluminium at the cathode.
• Aluminium loses electrons to become aluminium ions at the anode.
• Pure aluminium (about 99.9% pure) is withdrawn.

Aluminium Properties

• Aluminium appears as a silvery light metal which is malleable and ductile.
• Aluminium is a good conductor of heat and electricity.
• Its boiling point is 2050°C.
• Its melting point is 660°C.
• Aluminium reacts with air to form aluminium oxide (Al2O3).
• Aluminium reacts with nitrogen to form aluminium nitride (AlN).
• Aluminium reacts with steam to form aluminium oxide and hydrogen.
• Aluminium reacts with non-metals like chlorine to form aluminium chloride.
• Aluminium reacts with non-metals like sulphur to form aluminium sulfide.
• Aluminium reacts with alkalis to form sodium aluminate (NaAlO2).
• Aluminium reacts with hydrochloric acid (HCl) to produce aluminium chloride (AlCl3) and hydrogen gas (H2).
• Aluminium reacts with dilute sulfuric acid to produce aluminium sulfate (Al2(SO4)3) and hydrogen gas (H2).
• Aluminium reacts with concentrated sulfuric acid to produce aluminium sulfate (Al2(SO4)3), water, and sulfur dioxide (SO2).
• Nitric acid renders aluminium passive by forming a thin aluminium oxide layer.
• Aluminium is a reducing agent which reduces heated metallic oxides.

Uses of Metals

• Aluminium is used in alloys due to being strong, light, and corrosion-resistant.
• Aluminium is used in power cables being a good conductor of electricity.
• Aluminium alloys are used in ships because they are unaffected by sea water.
• Cast iron is used in drain pipes, gutter covers, weights, and railings.
• Wrought iron is used in chains, horse shoes and electromagnets.
• Steel is used in the construction of buildings, overhead structures, machines, and alloys.
• Zinc is mainly used for coating iron and steel sheets to prevent them from rusting.
• Zinc is used in alloys such as brass, bronze, and German silver.
• Zinc dust is used as a reducing agent for organic reactions.
• Zinc compounds are used in paints and for leather dying.

Alloys

• Alloys are homogeneous mixtures with metallic and non-metallic elements.
• Alloying modifies appearance and color.
• Alloying modifies chemical reactivity.
• Alloying modifies casting ability.
• Alloying lowers melting points.
• Alloying increases hardness and tensile strength.
• Alloying increases resistance to electricity.
• Brass consists of 60–80% copper and 40–20% zinc, used for utensils.
• Bronze consists of 2% zinc, 80% copper, and 18% tin, used for utensils, statues and coins.
• Duralumin consists of 95% aluminium, 4% copper, 0.5% manganese, 0.5% magnesium, used for aircraft bodies.
• Magnalium consists of 95% aluminium and 5% magnesium, used for balance beams and light instruments.
• Solder consists of 50–40% lead, 50–60% tin, used for soldering purposes.
• Stainless Steel consists of 73% iron, 18% chromium, 1% carbon, and 8% nickel, used for cutlery and utensils.
• Type metal consists of 75% lead, 10% tin, and 15% antimony, used for printing blocks.
• Manganese steel consists of 84% iron, 15% manganese, 0.9-1.5% carbon, used for safes and armour.
• Tungsten steel consists of 77-89.5% iron, 10-20% tungsten, 0.9-1.5% carbon, used for cutting tools.
• Alnico consists of 50% iron, 20% aluminium, 20% nickel and 10%cobalt, used for powerful magnets.
• Gun metal consists of 88% copper, 10% tin, 1% zinc and 1% lead, used for barrels of cannons, gears and bearings.
• German silver consists of 60-30% copper, 25-35% zinc, and 15-35% nickel, used for rheostats and resistors.
• Bell metal consists of 80% copper and 20% tin, used for bells and gongs.