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P -Block Elements


Posted Date: 18-Nov-2009  Last Updated:   Category: Education    
Author: Member Level: Gold    Points: 2






1.Group 14 elements show a covalency of four why.
Group 14 elements have a general electrons configuration of [rare gas]ns2 2p2.

2.What is catenation?
Catenation is a property of elements to form long chains of same atoms.

3.Catenation number of carbon is unlimited why?
Carbon has more catenation, because 4 valency electrons are present in 4 orbitals and the tetra valency of carbon is fully saturated.

4.How do the following properties vary down the group 14 in the periodic table?
Atomic size – increases down the group.
Electronegativity – decreases down the group.
Oxidation state – when np2 electrons are involved in bonding, they exhibit +2 oxidation state and +4 oxidation state is exhibited when ns2 np2 electorns are involved in bonding.
Melting point: decreases down the group.
Boiling point: decreases down the group.
Catenation: number decreases down the group.

5. Ionization potential of Pb is slightly more than that of tin. Why?
Pb has higher ionization energy that tin because the 5f- electrons shield less effectively in lead.

6.What is inert pair effect?
The ns2 electrons of Ge, Sn and pb remain inert and do not involve in bonding. This effect is called inert pair effect.

7.Write the allotropic forms of carbon.
Allotropic forms of carbon are Diamond, graphite, coal, coke, charcoal, carbon black and Fullerenes.

8.What are fullerenes?
Fullerenes are allotropic forms of carbon with giant spherical or ball type structures (C60 and C70)

9.Give the hybridization in diamond / graphite / fullerenes.
Diamond – sp3 hybridization
Graphite – sp2 hybridization
Fullerenes – sp2 hybridization


10.What is meant by intrinsic / n – type / p – type semiconductivity?
Intrinsic semiconductivity: It is the semiconductivity offered by pure substances like silicon and germanium.
n – type. Semiconductivity: This type of semiconductivity is offered when impurity atoms have excess of electrons when compared to the number have excess of electrons when compared to the number of electrons present in the host atoms.
p – type semiconductivity: It is the semiconductivity offered when impurity atoms have less number of electrons as compared to the number of electrons in the host atom.

11.Explain the variation of ionization potential among group 14 elements.

Ionisation energy decrease down the group from carbon to tin. Carbon has the highest ionization energy because its atom is the smallest in size among them.
Ionisation energy decreases sharply from carbon to silicon because atomic size increases and the force of attraction by the nucleus decrease.
The decreases in the ionization energy for germanium and tin are less because of the imperfect shielding of 3dand 4d orbitals.
pb has higher ionization energy than tin because the 5f – electrons shield less effectively in lead. Hence, the atomic size decreases and ionization energy increases.
12.Why does the metallic property increases down the group?
The metallic property increase down the group from carbon to lead due to the increase in atomic size.
C > S > Ge > Sn > pb
Non – metals Metalloid metals

13.What is the effect of heat on allotropic froms of tin?
When Grey tin is heated at 180C it gives white tin.


14.What is allotropy? Give example?
Allotropy is a property of elements in which they exist in more than one physically different forms.
Eg. (1) Carbon exists as diamond and graphite (2) Tin exists in three solid forms – grey tin, white tin and rhombic tin.

15.Explain the catenation of carbon.
Catenation is a property of elements to form long chains of same atoms. Carbon can form any length of carbon chain containing a large number of carbon atoms. The number of carbon atoms in the chain is known as catenation number. The catenation number of carbon is unlimited.

16.What is Fajan’s rule? Give one application.
Fajan’s rule states that ‘smaller the cation, the greater is the covalent character.
pb4+ is smaller than pb+2. Hence, pb4+ compounds are ionic.

17.What are the uses of Fullerenes?
1. Fullerenes can be used as super conductors at low temperature of 10 – 40 K.
2. They are also used as lubricants because of their spherical structure.


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Responses to "P -Block Elements "
Author: Asha Kurian    03 Aug 2010Member Level: Gold   Points : 1
Hi prabha
The symbol for lead is Pb.Here P should be in capital letter & b in small letter.Please note that it is not small p & small b. In the fifth point you have written like pb & in the answer it is Pb.

Regards
Asha



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