18.0     DEFINITION OF METAL

Metals are elements whose atoms ionize by electro loss while non – metals ionize by gaining electrons. Metal shows certain characteristics which distinguish them from non-metals. More than three quarter of all known elements are metals.

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            18.1     PROPERTIES OF METALS

PHYSICAL PROPERTIES

• High melting and boiling points.
• Characteristic lustre.
• Malleable i.e. can be hammered into sheets.
• Ductile i.e. can be drawn into wire.
• Sonorous, i.e. give off a note when hit.
• Hard but not brittle, with great tensile strength.
• Good conductors of heat and electricity.
• Relatively high densities.

CHEMICAL PROPERTIES

• Metallic atoms have great tendency to ionize and form positive ions by losing electron because they have few valence electrons. Thus, they are electropositive.
• Metals are reducing agents because they donate electrons readily during chemical reactions.
• Some metals react with acids to form salt by replacing the hydrogen ion (H+) from an acid.
• Most metals react with oxygen to form basic oxide which dissolve in water to form alkalis.
• Hydrogen form compound by covalency, and in acids by loss of electron to form hydrogen ion. but few very reactive metals force hydrogen to accept electron to form hydride, which are salt like solids.

18.2     EXTRACTION OF METALS

Extraction of metals is the process by which metals are isolated from their ore. The extraction of metal is a reduction process during which the metallic ions are reduced to their corresponding metal atoms. It is preceded by the concentration of metal ore to remove impurities through oil floatation, magnetic separation hydraulic washing. The method chosen for extraction of a particular metal depends on stability of the ore which in turn depends on the position of the metal in the reactivity series.

• ELECTROLYTIC PROCESS – This process is used for the extraction of the very reactive metals (potassium, sodium, magnesium, calcium and aluminum) which are very stable chlorides and trioxocarbonates. During electrolysis, cathode acts as a reducing agent by supplying electrons to the metallic ions in the electrolyte, resulting in the deposition of the free metal. Electrolytic processes are very expensive to install and maintain. They are used only when chemical or thermal reduction of the ore is not possible.

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• CHEMICAL REDUCTION – This is used to obtain the moderately reactive, less electropositive metals (Zn, Fe, Sn, and Pb) from their ores by reducing the oxides. The first method involves, reducing the oxides of metals with coke or carbon (II) oxide.

Fe₂O_3(s) + 3CO_(g) → 2Fe_(s) + 3CO_2(g)

The second method involves oxidation of sulphides to oxides followed by reduction of oxides.

2PbS_(s) + 3O_2(g) → 2PbO_(s) + 2SO_2(g)

2PbO_(s) + C → 2Pb_(s) + SO_2(g)

• THERMAL REDUCTION – In this process, metals are obtained from their ores by heating e.g.

HgS_(s) + O_2(g) → Hg_(s) + SO_2(g)

Elements at the bottom of reactivity series like copper, mercury, silver and gold are free metals.

            18.3     GROUP 1 ELEMENTS

• They are all metals except for hydrogen. These metals are commonly known as alkali metals because they react with water to form alkalis.
• They are univalent elements; readily ionizes and are good reducing agents.
• They are soft and light with low melting points; atoms are held together by weak metallic bonds.
• They are very reactive; reactivity increases down the group.
• Group 1 metals and their ions give characteristic flame colours.

SODIUM

• It is a Group 1 metal, extracted by electrolytic reduction of fused sodium chloride in the Downs cell.
• It is a soft, silvery metal with a relative desnsity of 0.98 and a low melting point of 97^oC.
• It is very reactive, readily combining with the atmospheric gases and has to be stored under oil. Sodium is used in streetlamps and in the manufacture of compounds like sodium peroxide and sodamide.

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COMPOUNDS OF SODIUM

• They are ionic solids with high melting points; soluble in water and are white unless the anion is coloured.
• SODIUM HYDROXIDE / CAUSTIC SODA – It is manufactured by electrolysis of brine. Sodium hydroxide, NaOH, reacts with the ions of Al, Zn and Pb to precipitate their hydroxides. It is used in manufacturing of soap, rayon and paper; water purification, bauxite purification, petroleum refining etc.
• SODIUM TRIOXOCARBONATE(IV) / WASHING SODA – It is manufactured by the Solvay process from sodium chloride and calcium trioxocarbonates. It is used in glass manufacturing, water softening and detergent production.
• SODIUM CHLORIDE – It is obtained from rock salt and sea water; extracted through evaporation and other methods. It is a dietary requirement and a common food preservative. It is used in the manufacture of many compounds such as sodium hydroxide.

18.4     GROUP 2 ELEMENTS

• They are metals known as alkaline earth metals. They are divalent elements; readily ionize to form divalent positive ions.
• They are reactive but less than the Group 1 metals. Their atoms are held together by a stronger metallic bond than that of Group 1.

Like alkali metals, Group 2 metals and their ions give characteristic flame colours.

CALCIUM

• It occurs naturally as calcium trioxocarbonates(IV) in limestone, chalk, seashell and marble.
• It is extracted by the electrolysis of the fused chloride.
• Calcium reacts readily with water, carbon(IV) oxide and oxygen in the air.
• It is an essential dietary requirement, needed for the development of healthy bones and teeth.

COMPOUNDS OF CALCIUM

• CALCIUM OXIDE / QUICK LIME, CaO – It is made by heating limestone (CaCO₃) or seashell in a process known as calcination. It is used to make slake lime, calcium carbide; to treat acidic soils; and to neutralize acidic wastes in industry.
• CALCIUM HYDROXIDE / SLAKE LIME, CaOH – It is made by adding water to calcium oxide. It is used to treat acidic soil and make mortar (an important building material).
• CALCIUM TRIOXOCARBONATE(IV) / CALCIUM CARBONATE – It is found in limestone. Calcium carbonate, CaCO₃, is a major raw material in the chemical industry. It is used for the extraction of iron; and for the making of glass, quicklime and cement. Cement and concrete (made from cement) are important building materials.

18.5     GROUP 3 ELEMENTS

• All Group 3 elements are metals except Boron.
• They are trivalent elements and tend to form more covalent compounds than ionic ones.

ALUMINUM

• It is abundant in the earth’s crust, found as trioxosilicates(IV) in rocks and clays.
• The main ore of aluminum is the mineral bauxite (Al₂O₃. 2H₂O). Other ores include kaolin, cryolite, corundum and mica.
• Aluminum is extracted from its oxide ore (bauxite) by electrolysis of the molten oxide.
• The Bayer process is used to purify bauxite.
• It reacts with oxygen in the air to form an oxide which forms a thin continuous coating over the metal. This makes aluminum corrosion-free and passive.
• It is amphoteric in nature; reacts both with acids and alkalis.
• It reduces iron(III) oxide to molten iron. This reaction is used in the Thermit process to weld broken metallic parts.
• Aluminum is used for making cooking utensils and over-head electric cables. Its alloys are used for making the body parts of aircrafts.

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COMPOUNDS OF ALUMINUM

• ALUMINUM OXIDE / ALUMINA – It is prepared by heating aluminum hydroxide. It is amphoteric in nature. Al₂O₃ is used to make furnace linings and in the catalytic cracking of hydrocarbons.
• ALUMINUM HYDROXIDE – Al(OH)₂ is precipitated when sodium hydroxide is added to an aqueous solution of an aluminum salt. It is used as a mordant in dyeing cloth.
• ALUMINUM TETRAOXOSULPHATE(VI) – It occurs naturally but can be manufactured by the action of hot concentrated tetraoxosulphate(VI) acid on aluminum oxide. Al₂(SO₄)₃ forms alum with other tetraoxosulphate(VI). It is used in the treatment of water and sewage; and in paper production.

18.6     GROUP 4 ELEMENTS

• They change from non-metals (carbon) to metals(tin and lead) as we go down the group.
• They are tetravalent elements; tends to form covalent compounds.
• They have oxidation state of +4 in their compounds; tin and lead also have an oxidation state of +2 in their covalent compounds.

TIN

• It occurs as the oxide ore, cassiterite or tin stone (SnO₂).
• It is extracted by roasting the ore in the air to remove impurities, and then heating the concentrated ore with powdered charcoal to reduce the tin(IV) oxide to the metal. The impure tin formed is purified by remelting.
• It exist in three different allotropic forms – Grey tin, White tin and Rhombic tin.
• Tin is corrosion-resistant and has a low melting point.
• It is used in soldering, coating other metals to prevent corrosion (e.g., tin plating), and in the production of alloys like bronze.

COMPOUNDS OF TIN

• TIN(II) OXIDE – It is a grey white solid made by heating tin(II) ethanedioate  or tin(II) hydroxide in an inert atmosphere. SnO is amphoteric in nature.
• TIN(IV) OXIDE – It is occurs naturally as cassiterite and can be made by heating tin strongly in air, by dissolving tin in concentrated trioxonitrate(V) acid or by hydrolyzing tin(IV) chloride. SnO₂ is a white solid that is insoluble in water and generally insoluble in acids. It is used industrially to make white enamel and tiles. Its also amphoteric in nature.
• Tin(II) Hydroxide.
• Tin(II) Chloride; Tin(IV) chloride.
• TIN(IV) HYDRIDE – An unstable compound of tin, which decomposes at room temperature.

18.7     TRANSITION METALS

Transition metals are found in the d-block of the periodic table (between Group 2 and 3). A transition metal may be defined as an element with a partially filled d-orbitals. The first transition series is found in Period 4. The atoms of these metals have one or two electrons in the 4s orbital and partially filled 3d orbitals.

• Atoms of transition metals are held together by a stronger metallic bond; these metals are strong and hard with higher melting and boiling points than the s-block metals.
• They also have smaller atoms than the corresponding s-block metals.
• The atoms are tightly packed in their crystal lattice, making these metals very dense.
• They are moderately active, having higher ionization energy than the s-block metals.

Due to a partially filled d-orbital, transition metals have the following characteristic properties:

• Variable oxidation state e.g. Fe²⁺, Fe³⁺, Cu⁺, Cu²⁺.
• Ability to form complex ions e.g. [Fe(CN)₆]³⁻.
• Presence of coloured ions due to d-d electron transitions e.g. Cu²⁺ is blue.
• Ability to act as catalysts in chemical reactions e.g. Fe in the Haber process.

IUPAC NAMES OF SOME TRANSITION COMPLEXES

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            18.8     IRON

• It is mainly extracted from its ores by chemical and thermal reduction in a blast furnace. It is also extracted by a direct reduction process which is used at the Aladja steel-works.
• Haematite, magnetite, iron pyrites, siderite and limonite are the most common iron ores.
• Iron is a typical transition metal which exhibits +2 and +3 oxidation states in its compounds. The +3 state is more stable because of the half-filled d orbitals in the iron(III) ions.
• Pure iron is a fairly soft malleable metal which is magnetic (ferromagnetic).
• In the presence of moist air, iron rust due to the formation of a reddish-brown hydrated iron(III) oxide which forms a porous layer over the metal. Rusting is prevented by painting the metal or coating it with other corrosion-free metals like tin or zinc.
• An aqueous solution of iron(II) oxide is pale green in colour, while iron(III) is yellow.
• Iron forms many complex ions.
• There are three types of iron – Pig iron, Cast iron and Wrought iron (the purest form of commercial iron).
• Steel is an important alloy of iron. It contains 90% of pig iron.
• Iron is extensively used in building and construction industry, making of machineries,tools and vehicle body parts
• Iron (Fe²⁺ and Fe³⁺) – Fe²⁺ forms a green precipitate with NaOH, while Fe³⁺ forms a brown precipitate with NaOH.

18.9     COPPER

• Copper, Cu, is extracted from its ore by chemical and thermal reduction. The metal is purified by electrolysis.
• It is a reddish-brown, extremely malleable metal which is a good conductor of heat and electricity.
• It is not a reactive metal. In moist air, copper becomes covered in green coating of basic copper(II) tetraoxosulphate(VI) and trioxocarbonate(IV).
• Copper exhibits +1 and +2 oxidation states in its compounds. The +2 state is more stable.
• In aqueous solution, the ions are extensively hydrated. The hydrated copper(II) ions are blue in colour. Copper ions also form many coloured complexes with other ions and molecules.
• Copper(I) ions undergo disproportionation in aqueous solution to give copper(II) ions and metallic copper.
• Copper is used for making electrical wires, ornamental objects, coins, heat exchangers; in plumbing etc.
• Test for Cu²⁺ – Formation of a blue precipitate with sodium hydroxide.
• Brass and Bronze are important alloys of copper.

18.10   ALLOYS

An alloy is a substance prepared by adding one or more elements to a base metal to give it certain desirable qualities. Alloys are designed to enhance the properties of their constituent elements, resulting in materials with improved strength, durability, corrosion resistance, and other beneficial characteristics.

Here are some examples of alloy, their primary components and uses with the aid of diagram.