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CBSE Class 12th Chemistry Notes for Chapter 7 The P-Block Elements

                    UNIT 7 THE p-BLOCK ELEMENTS


  • Groups 13 to 18 of the periodic table consist of p-block elements with their valence shell configuration ns2 np1-6.


  • Group 15 consists of five elements: N, P, As, Sb, Bi which have general electronic configuration ns2np3.


  • Nitrogen differs from other elements of this group due to small size, formation of pπ- pπ bonds with itself and with highly electronegative atom like O or C and non-availability of d orbitals to expand its valence shell.


  • Elements of group 15 show gradiation in properties. They react with oxygen, hydrogen and halogens. They exhibit two important oxidation states, +3 and +5, but +3 oxidation state is favoured by heavier elements due to ‘inert pair effect’.


  • Dinitrogen can be prepared in laboratory as well as on industrial scale. It forms oxides in various oxidation states as N2O, NO, N2O3, NO2, N2O4 and N2O These oxides have resonating structures and have multiple bonds.


  • Haber’s process: This process is used to prepare ammonia on a large scale.


  • HNO3 (nitric acid) is an important industrial chemical. It is a strong monobasic acid and is a powerful oxidizing agent.


  • Phosphorus exists as P4 in elemental form. It exists in several allotropic forms. It forms hydride, PH3 which is a highly poisonous gas. It forms two types of halide as PX3 and PX5. PCl3 is prepared by the reaction of white phosphorus with dry chlorine while PCl5 is prepared by the reaction of phosphorus with SO2Cl2. Phosphorus forms a number of oxoacids. The oxoacids which have P-H bonds are good reducing agents.


  • The group 16 elements have general electronic configuration ns2np4. They show maximum oxidation state +6.


  • Dioxygen is prepared in the laboratory by heating KClO3 in the presence of MnO2. It forms a number of oxides with metals. Allotropic form of oxygen is O3 which is a highly strong oxidizing agent.


  • Sulphur forms a number of allotropes. Of these, α- and β- forms of sulphur are the most important. Sulphur combines with oxygen to give oxides such as SO2 and SO3. SO2 is prepared by the direct union of sulphur with oxygen and is used in the manufacture of H2SO4.


  • H2SO4 is prepared by contact process. It is a dehydrating and oxidizing agent.


  • Group 17 consists of the following elements: F, Cl, Br, I and At. These elements are extremely reactive and as such they are found in combined state only. The common oxidation state of these elements is -1.


  • They form oxides, hydrogen halides, interhalogen compounds and oxoacids.


  • Chlorine is obtained by the reaction of HCl with KMnO4.


  • Halogens combine with one another to form interhalogen compounds.




  • Group 18 consists of the noble gases. They have ns2np6 valence shell electronic configuration except He which has 1s2. All gases except Rn occur in the atmosphere. Rn is obtained as the decay product of 226


  • Due to complete octet of outermost shell, they have fewer tendencies to form compounds. The best characterized compounds are those of xenon with fluorine and oxygen only under certain conditions. These gases have several uses like Argon is used to provide inert atmosphere, helium is used in filling balloons for meteorological observations and neon is used in discharge tubes and fluorescent bulbs.

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