Question

The melting point of Cu is higher than that of Zn because:
A. The s, p as well as d-electrons of copper are involved in metallic bonding.
B. The atomic volume of copper is higher.
C. The d-electrons of copper are involved in metallic bonding.
D. The s as well as d-electrons are involved in metallic bonding.

Answer 1

Hint: The melting point of transition metals are correlated with the no. of unpaired electrons present. Copper has a melting point of 1085$^\circ$C while Zinc has a melting point of 419.5$^\circ$C. Both Copper and Zinc have 10e- in its 3d orbital.

Complete step by step solution:
-Copper has an electronic configuration of \[\left[ Ar \right]3{{d}^{10}}4{{s}^{1}}\] , while Zinc has an electronic configuration of \[\left[ Ar \right]3{{d}^{10}}4{{s}^{2}}\]. During metallic bond formation the d-electrons of Copper are involved, so large amounts of free electrons are present, thus increasing its melting point.
 - Copper and Zinc both have almost similar atomic weight (Cu-63.546g/mol, Zn-65.38g/mol). But there is a difference in their density values which are Cu-8.96g/mL and Zn-7.14g/mL. This is due to the difference in their packing structures. Copper has an ccp(cubic close packing) arrangement while Zinc has hcp(hexagonal close packing) arrangement. Thus, due to the difference in density, the melting point of Copper is greater than Zinc.
Therefore, the answer to the question is option (c).

Additional information:
-Copper is reddish in colour and takes a bright metallic luster. It is malleable, ductile and is a very good conductor of electricity.
- Copper is extracted from pyrites. It usually occurs in combined states like copper sulphide, malachite etc.
-Due to Cu high conductivity is used in the making of electric cables and other electric goods.
- Copper is weakly electropositive and it is not very reactive.
- Zinc also occurs mainly in combined states such as Zinc Blend, Calamine etc.
- It has a bluish white metallic lustre which on reaction with air form is carbonate.
- Zinc is mainly used in preparation of alloys such as Brass, Delta metal and german silver.
- Zn in ordinary temperatures in brittle, at 428K becomes malleable and ductile. This change is because of its different allotropic forms.
- Zinc has a very important biological role. It is seen in certain enzymes and its proper functioning depends on the amount of zinc present. Such enzymes play an important role in digestion of proteins.

Note: It is often mistaken that only the s electrons of Cu participate in metallic bonding. This is not the case. But p-electrons of Cu are not involved in metallic bonding.