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The p-Block Elements -CBSE Class 12th NCERT Solution

Aug 2, 2013 14:31 IST

Get, detailed solutions to the questions of the chapter: The p-Block Elements from NCERT textbooks. The objective is to helping students regarding the pattern of answering the question as per the cbse latest marking scheme. Cbse.jagranjosh.com provided you NCERT solutions for classes 12th math and science subjects.


Some questions with answer of this chapter are given here

Q. Discuss the general characteristics of Group 15 elements with reference to their electronic configuration, oxidation state, atomic size, ionisation enthalpy and electronegativities


General characteristics of group 15 elements are:

a) Electronic configuration
Elements of group 15 have 5 valence electrons. Their general electronic configuration is ns2 np3.

b) Ionization energy
On moving down a group, first ionization energy decreases. This happens because of increasing atomic sizes.

c) Electronegativity
On moving down a group, electronegativity decreases

d) Oxidation states
Elements of this group have 5 valence electrons and they require three more electrons to complete their octets. But, gaining electrons is very difficult in nitrogen as the nucleus will have to attract three more electrons. The remaining elements of this group show oxidation state of −3. In addition to the −3 state, N and P also show −1 & −2 oxidation states.

All the elements present in this group show +3 and +5 oxidation states. However, the stability of +5 oxidation state decreases down a group, whereas the stability of +3 oxidation state increases. This happens because of the inert pair effect.

e) Atomic size:
On moving down a group, atomic size increases. This happens because of increase in the number of shells.


Q. Why does the reactivity of nitrogen differ from phosphorus?


Electronic configuration of nitrogen is half filled & we know that fully filled & partially filled orbitals are quiet stable. Being, smaller in size, nitrogen is chemically less reactive. Whereas when we move down the group, size of atom increases, thus, other elements of this group do not exhibit this property. As size increases, effective nuclear charge of atom decreases & it can lose & gain electrons easily & show reactivity towards other elements. Thus, phosphorus is more reactive than nitrogen.

Q. Discuss the trends in chemical reactivity of group 15 elements.


General trends in chemical properties of group – 15

a) Reactivity towards hydrogen:
Group 15 elements react with hydrogen & form hydrides having formula EH3, where E = N, P, As, Sb, or Bi. The stability of hydrides decreases on moving down from NH3 to BiH3.

b) Reactivity towards oxygen:
Group 15 elements form two types of oxides: E2O3 and E2O5, where E = N, P, As, Sb, or Bi. The oxides having higher oxidation state are more acidic than the other. However, the acidic character decreases on moving down a group.

c) Reactivity towards halogens:
The group 15 elements react with halogens to form two types of salts: EX3 and EX5. But, nitrogen does not form NX5 as d-orbitals are absent in it.

d) Reactivity towards metals:
On reaction with metals, group 15 elements form binary compounds in which metals exhibit −3 oxidation states.


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