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metallurgy 2

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METALLURGY I 1. Physical differences between metals and non-metals : Metals Non-metals (a) Metals are generally solids at the room temperature. Exception : Mercury is a liquid at the room temperature. (b) Metals are generally hard. Exception : Sodium, potassium, lead, gold and magnesium. (c) Metals have a lustre and can be highly polished. (d) Metals generally have a high density. Exception : Sodium and potassium are lighter than water. (e) Metals generally have a high m.p. and b.p. Exception : Sodium and potassium have a low m.p. and b.p. (f) Metals are generally malleable and ductile. Exception : Zinc, antimony, arsenic and bismuth are not malleable. (g) Metals generally have a very high tensile strength. Exception : Zinc, arsenic, antimony and bismuth. (h) Metals are generally good conductors of heat and electricity. Exception : Bismuth and tungsten are poor conductors of electricity. (i) Metals in the molten state dissolve in each other to form alloys. (a) Non-metals are gaseous or liquids or brittle solid at the room temperature. (b) Non-metals are generally soft. Exception : Diamond is the hardest naturally occurring allotrope of carbon. (c) Non-metals do not have any lustre. (d) Non-metals generally have low density. Exception : Diamond is almost as heavy as aluminium. (e) Non-metals generally have a low m.p. and b.p. Exception : Carbon, silicon and boron have a high m.p. and b.p. (f) Non-metals are generally nonmalleable and non-ductile. They are brittle in nature, if solids. Exception : Carbon fibre, an allotrope of carbon, is very ductile. (g) Non-metals do not have a high tensile strength. Exception : Carbon fibre is as tensile as steel. (h) Non-metals are generally poor conductors of electricity. Exception : Gas carbon and graphite are good conductors of electricity. (i) Non-metals do not form alloys. 1 Key Points (j) Metals are insoluble in water and other solvents, unless they react chemically. (j) Non-metals are generally soluble in water or other solvents and do not react with them chemically. 2. Chemical differences between metals and non-metals : Metals Non-Metals (a) Metals have one to three electrons in their valence shell. Exception : Hydrogen, which has one electron in its valence shell. (b) Metals readily lose valence electrons to form cations. (a) Non-metals have four to seven electrons in their valence shell. Exception : Hydrogen, which has one electron in its valence shell. (b) Non-metals either gain electrons or share electrons, in order to enter in a chemical reaction. Na e Na + O + 2e O 2 (c) Metals are reducing agents and by themselves are oxidised. (c) Non-metals are oxidising agent and by themselves are reduced. Exception : Carbon is oxidised and is a reducing agent. (d) When metallic compounds are electrolysed, the cations are discharged at the cathode. (d) The non-metallic anions during electrolysis are discharged at the anode. Al+3 + 3e Al O 2 2e O (e) Metallic oxides are basic in nature. (e) Non-metallic oxides are acidic in nature. (f) Non-metallic oxides are covalent in nature and don t conduct electricity. (g) Non-metals generally react with hydrogen to form their hydrides. (h) Non-metals do not react with dilute mineral acids to liberate hydrogen. (f) Metallic chlorides are electrovalent in nature and conduct electricity. (g) Metals (except Na, K and Ca) do not react with hydrogen. (h) Metals (active metals), generally react with dilute mineral acids to liberate hydrogen. 2 Key Points 3. Metalloids : The elements which exhibit some properties of metals and some properties of non-metals are called metalloids. Arsenic, antimony, bismuth and germanium are metalloids. 4. Alloy : A homogeneous solid solution of two or more metals which are mixed in the molten state in fixed proportion is called an alloy. Table for common alloys Name of Alloy 1. Duralumin or Dural Principal Composition Metal Aluminium Al (95%); Cu (4%) Mn (0.5%); Mg (0.5%) 2. Magnalium Aluminium Al (95%); Mg (5%) 3. Stainless steel Iron 4. Manganese steel Iron manganese 5. Tungsten steel Iron 6. Alnico Iron 7. Elektron Magnesium Mg (95%) Fe (82% to 84%) Cr (12% to 14%) C (0.5% to 1.5%) Ni (1% to 2%) Fe (83.5% to 84%) Mn (15%) C(0.9% to 1.5%) Fe (77.5% to 89.5%) W (10% to 20%) C (0.9% to 1.5%) Fe (50%) Al (20%) Ni (20%) Co (10%) 3 Properties Lightweight and as strong as steel Lightweight, strong and resists corrosion Resists corrosion Very tough and hard Uses Aircraft frames, rockets, automobiles Aircraft, household appliances, mirrors, scientific instruments Utensils, cutlery, surgical instruments, ornamental piece Safes, armour plates, rock cutters Very, very hard Used for making high speed machine tools Highly Used for making ferromagnetic powerful magnets in nature which can lift 4000 times of their own weight Strong and Used for making Key Points Zn (5%) Cu (90%) Al (9.5%) Sn(0.5%) Cu(60% to 80%) Zn (40% to 20%) durable Golden in colour and durable Easily moulded, good conductor of heat and electricity. Hard and brittle, takes very high polish Very hard, gives a good cast engineering goods Making artificial jewellery, coins, picture frames. Making gun shells utensils etc. Used for making imitation silver jewellery, decoration pieces and utensils Used for making bells and gongs 8. Aluminium Bronze Copper 9. Brass Copper 10. Bronze Copper Cu (80%) Zn (2%) Sn (18%) 11. Gun metal Copper Cu (88%) Sn (10%) Zn (1%) Pb (1%) 12. German silver Copper Cu (60% to 30%) Zn (25% to 35%) Ni (15% to 35%) White as silver, malleable and ductile 13. Bell metal Copper Cu ( 80%) Sn (20%) 14. Solder Tin Sn ( 50% to 60%) Pb (50% to 40%) Hard and brittle, produces sonorous sound Low m.p., unacted by air and water 15. Type metal Lead Pb (70%) Sn (10%) Sb ( 20%) 4 Hard, expands on cooling, low m.p. Making coins, utensils, and statues Used for making barrels of gun, gears and bearings Used for soldering purposes of electric fuses Used for making printing type Key Points

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