Question

Metallic bonds are the chemical bonds that hold together in metals. They differ from covalent and ionic bonds because the electrons in the metallic bonding is delocalized, i.e., they are not shared between only two atoms. Instead, the electrons in metallic bonds float freely through the lattice of the metal nuclei. This type of bonding gives metals many unique material properties including excellent thermal and electrical conductivity, high melting melting points, malleability and ductility. 

Now answer the following questions : 

(i) Which metal is used in making the filament of electric bulbs and why? 

(ii) Which metal is generally used for making target to be hit by cathode rays in an X- rays tube and why? 

(iii) Why metals are used in the form of their alloys? 

(iv) Why steel vessels with copper base/bottom are preferred over steel vessels for the heating on the flame? 

(v) Iron is cheaper than copper. Then why copper wire are used in the electric wires but not iron wires? 

(vi) Which alloy is used in making heating elements and why?

Answer 1

(i) Tungsten is used because it has very high melting point. 

(ii) Mollebdenum is generally used because it is a hard metal. 

(iii) Pure metals may not have the desired properties. By alloying them with a metal or a non-metal, we can have the desired properties depending upon the use. 

(iv) Copper has excellent thermal conductivity as compared to steel. Hence, steel vessels with copper bottom are preferred for heating on the flame. 

(v) Copper has a very high electrical conductivity as compared to iron.hence copper wires are preffered over iron wires. 

(vi) Nicrome alloy (80% Ni, 20-% Cr) is used for making heating elements because it is very resistant to oxidation.