Engineering Chemistry S Datta

14
Metallurgy
INTRODUCTION TO THE STUDY OF METALS
The gold and silver among the metals are probably the first used by man. The art of reducing
copper ores and tin ores, and producing bronze dates back to 300 B.C. In history we find ‘stone
age’ followed by ‘bronze age’ and ‘bronze age’ followed by ‘iron age’.
Today we find the metals are very extensively used in art and industry. Iron in the form
of steel, wrought iron and cast iron is used in constructing bridges, dams, pipes, tubes and
machine parts. Copper is another important metal being used mainly in electrical articles.
Nowadays almost all the metals have some specific uses.
Metals
Metals are the elements, which occupy the left hand side of the periodic table with one,
two or three electrons in the outermost shell that takes part in bonding and chemical
reactions.
Physical Properties of Metals
Metals are:
• Shiny when freshly polished and free of corrosion.
• Good conductors of heat and electricity.
• Malleable and ductile.
• Generally solids are with high m.p. and b.p. (only six metals melt below 100 °C—Hg
which is a liquid and four group I metals: Na, K, Rb, Cs).
Major Chemical Properties of Metals
Chemically, metals tend to:
• Lose electrons to form cations or positive ions i.e., metals are reducing agents.
• Form basic or amphoteric oxides.
• Form solid ionic chlorides.
The more an element exhibits these properties, the greater is its “metallic character”.
Metallic Bonds
Metallic bonds are strong bonds in metal crystals. Each metal atom in a metal crystal
contributes electrons from its outermost shell to form a “sea of delocalised electrons”. Only
elements with low first ionisation potential form metallic crystals. When a metal atom looses
electron it becomes positively charged. So, it is quite likely that a metal crystal consist positively
charged metal atoms embedded in a sea of shared electrons.
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