Introduction:
Metals and their compounds are the most common and important substances that have been used by people for different purpose. Metals like iron or steel is used for construction work, manufacturing weapons, machinary parts in industries, household utensils etc.
Metals like aluminum is used in making coins, electric cables, household utensils and many more.
Not only metals, but also their compounds have immense importance in our daily life.
Metals and Non-metals
There are more than 115 elements known so far. Among them maximum 79 are metals. The elements which shows dual properties of metal and non-metal which are termed as metalloids.
Physical properties
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Metals
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Non-Metals
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Physical state
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Metals are solid at normal temperature. Mercury is an exception.
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Non-metals are in all three states e.g.: solid, liquid and gas.
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Appearance of the surface
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Freshly cut surface of a metal has a bright appearance i.e. metallic lustier.
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Surface of non-metallic elements look dull i.e. has no metallic lustier.
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Density
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Metals have high density. Exception- alkali metals
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Non- metals have generally low density.
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Hardness
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Metals are hard with varying degrees of hardness.
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Generally, non-metals are soft. Exception- diamond.
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Melting and boiling points.
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Generally metals have high melting and boiling points. Exception- alkali metals and mercury.
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Non-metals have generally a low M.pt. and B.pt. Exception- carbon, silicon.
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Malleability
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Metals can be hammered into thin sheets i.e. malleable or drawn into thin wires i.e. ductile.
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Non-metals are not malleable and ductile i.e. non-metals are brittle. Exception: As, Sb, Bi.
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Conductivity
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Metals conduct heat and electricity i.e. are good conductors of heat and electricity.
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They are poor conductors of heat and electricity. Exception: graphite form of carbon.
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Alloy formation
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Metals dissolve each other to form a homogeneous mixture called alloy.
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Non-metals generally do not form alloy.
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Electrochemical property
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Metals are generally electropositive i.e. form positively charged ions.
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They are normally electronegative i.e. form negatively charged ions.
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Chemical properties
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Nature of oxides
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Metals form basic oxides. Metal oxides dissolve with acid to form sald and water. Exception: Cr2O3, Mn2 O7, SnO2
2Mg + O2 ---> 2MgO
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Non-metals form acidic oxides. These oxides dissolve in a base to form salt and water. Exception: CO, N2O, NO, H2O.
C + O2 ---> CO2
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Nature of hydrides
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Only some metals combine with hydrogen to form unstable hydrides. Eg: NaH, CaH2.
2Na + H2 ---> 2NaH
Ca + H2 ---> CaH2
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Non-metals form stable hydrides with hydrogen.
C + 2H2 ---> CH4
N2 + 3H2 ---> 2NH3
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Action with acids.
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Most metals dissolve in acid to form a salt and a gas.
Mg + 2HCL ---> MgCl2 + H2
Zn + H2SO4 ---> ZnSO4 + H2
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Non-metals may dissolve in acid but gas is not formed.
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Ores and minerals: The compounds that occur naturally and have a characteristic chemical composition are called minerals. Metals are extracted from these minerals.
A mineral that is rich with the desired compound from which a metal or other element is extracted economically is called ores.
Metallurgy: The branch of science concerned with the extraction of metals from their ores and utilizing them for useful purpose is called metallurgy.
The method by which a metal is obtained from an ore depends on the nature of the ore. But the general methods that can be applied for the extraction of most metals can be listed as follows:
i. Crushing and Pulverization
ii. Dressing or concentration
iii. Roasting and calcination
iv. Smelting
v. Purification or refining
i) Crushing and Pulverization: The process of breaking big boulders of ores into small pieces is carried out by a crusher called crushing. The crushed ore is taken into pulverising mill where it is ground into fine powder. It is called Pulverization.
ii) Concentration or dressing of ores: This is the process of removing unwanted impurities from ores. This operation makes the ores rich with desired compounds only. Depending on the nature of ores, various methods like gravity separation, magnetic separation, froth flotation process may be employed. You are not studying evey detail of these processes at this layer.
iii) Roasting and calcination: This is the process in which concentrated ore is heated in the presence of air below its melting point. Calcination is the process of heating ores in the absence of air. The calcination is done to remove volatile matters, organic matters, and moisture from the ores. This process converts the ores into respective metal oxides.
iv) Extraction of the free metal: Free metal is obtained from the oxide ores by one of the following methods:
a. Reduction of oxides by using powerful reducing agents called smelting and,
b. Electrolytic reduction
v) Purification or refining: The metal obtained by the methods explained above is very rarely pure. It needs to be refined further by the process like electrolytic refining, zone refining, etc. One can obtain 99.99% purity of a metal by electrolytic refining.
Questions: What is roasting of ores?
Questions: How do metals occur in the nature?
Questions: What is metallurgy? What is its importance?
Questions: Write down the process for the extraction of metals?
