Question

The correct order of melting point of 14th group elements is:
A.$C> Si> Ge> Pb> Sn$
B.$C< Si< Ge< Sn< Pb$
C.$Sn> Pb> Ge> Si> C$
D.$Si> C> Ge> Sn> Pb$

Answer 1

Hint: The 14th group of elements in the periodic table is the carbon group. The carbon group or carbon family consists of six elements which are carbon, silicon, germanium, tin, lead and flerovium. They are represented by the symbols C, Si, Ge, Sn, Pb and Fl respectively. Each of the elements of the carbon group in the periodic table has four electrons in their outermost shell.

Complete step by step answer:
-All these are p-block elements. The elements carbon and silicon are typical non-metals. On the other hand, germanium is a semi-metal whereas tin and lead are typical metals. Thus, it can be said that down the carbon group, the character of the elements shifts from non-metallic to metallic.
-All the elements above lead usually form covalent bonding with other surrounding atoms. At the top of the group, carbon forms large covalent network structures in its two most familiar allotropes of diamond and graphite. These types of covalent structures are also found in silicon and germanium.
-Covalent structure is also found in one allotrope of tin called grey tin. But in another allotrope called white tin, tin shows distorted close packed metallic bonding. Thus, in heavier elements of the group such as in lead, the atoms are arranged in a close-packed 12- coordinated metallic structure. Thus, we can understand that as we move down towards the group, the metallic bonding structure tends to become more stable.
-Since covalent and metallic bonding lead to higher melting points, the melting point values of the group decreases from carbon to lead due to decrease in attractive forces. Very high melting points of carbon and silicon are due to their tendency to form giant covalent molecules. Tin and lead will have lower melting points but lead, as an exception, has higher melting point than tin due to the distortion in tin’s close-packed 12-coordinated structure.
So, the correct order will be C>Si>Ge>Pb>Sn.

So, the correct option is A.

Note:
The melting and boiling points of elements of the carbon family is much higher than the corresponding elements of the boron family. This is because atoms of group 14 elements can form 4 bonds with each other and so strong binding forces exist between their atoms in solid as well as gaseous states.