CBSE Class 11 Chemistry The P Block Elements Notes Set B

The p-block elements Elements in which the last electron enters in the any one of the three p- orbital of their outermost shells – p-block elements

• Gen. electronic configuration of outer shell is ns²np^1-6

The inner core of e-config.may differ which greatly influences their physical & to some extent chemical properties.

• The block of elements in the periodic table consisting of the main groups :

• Group 13            (B to Tl)

• Group14            (C to Pb)

• Group15            (N to Bi)

• Group 16           (O to Po)

• Group17            (F to At)

• Group18            (He to Rn)

(1) Members at the top and on the right of the p-block are nonmetals (C, N, P, O, F, S, Cl, Br, I, At).

(2) Those on the left and at the bottom are metals (Al, Ga, In,Tl, Sn, Pb, Sb Bi, Po).

(3) Between the two, from the top left to bottom right, lie an ill-defined group of metalloid elements (B, Si, Ge, As, Te)

GROUP 13 : The boron group

•Outer Electronic Configuration:-ns²np¹

• group members: boron (B), aluminum (Al), gallium (Ga), indium (In)& thallium (Tl) . All, except boron, are metals.

• Boron show diagonal relationship with Silicon; both are semiconductors metalloids & forms covalent compounds.

• Boron compounds are electron deficient, they are lack of an octet of electrons about the B atom .

• diborane B₂H₆, is simplest boron hydride

• Structure: three-center two-electron: the H atoms are simultaneously bonded to two B atoms the B-H bridging bond lengths are greater than B-H terminal.

• - Boron oxide is acidic (it reacts readily with water to form boric acid)

• aluminium compounds:aluminium oxide is amphoteric

• aluminum The sharp decrease in I.E. from B to Al is due to increase in size. In case of Ga, there are ten d-electrons in its inner electronic configuration. The very high value of 3rd I. E. of thallium indicates that +3 O.N. state is not stable, rather +1 is more stable for thallium . Electropositive (or metallic) character the elements of group 13 are less electropositive as compared to elements of group 2. On moving down the group the electropositive (metallic) character increases because ionization energy decreases. For e.g., Boron is a non-metal white the other elements are typical metals. Oxidation states The common oxidation states of group 13 elements are +3 and + l .The stability of the + 1 oxidation state increases in the sequence Al <Ga< In <Tl, Due to Inert pair effect.halides, e.g., AlC_l3 is dimer, an important catalyst in organic chemistry have anincomplete octet, acts as Lewic acid by accepting lone pairs from Lewic bases, forming adduct

• aluminum hydride, e.g., LiAlH₄, a reducing agent

• Atomic Properties - Electronic Configurations

. Atomic and ionic radii

• The atomic and ionic radii of group 13 elements are compared to corresponding elements of group 2. From left to right in the period, the magnitude of nuclear charge increases but the electrons are added to, the same shell. These electrons do not screen each other, therefore, the electrons experience greater nuclear charge.

• In other words, effective nuclear charge increases and thus, size decreases. Therefore, the elements of this group have smaller size than the corresponding elements of second group.

• On moving down the group both atomic and ionic radii are expected to increase due to the addition of new shells. However, the observed atomic radius of Al (143 pm) is slightly more than that of Ga (l35 pm). 

Ionization energies

The first ionization energies of group 13 elements are less than the corresponding members of the alkaline earths.

The sharp decrease in I.E. from B to Al is due to increase in size. In case of Ga, there are ten d-electrons in its inner electronic configuration. The very high value of 3^rd I. E. of thallium indicates that +3 O.N. state is not stable, rather +1 is more stable for thallium .

Electropositive (or metallic) character the elements of group 13 are less electropositive as compared to elements of group 2. On moving down the group the electropositive (metallic) character increases because ionization energy decreases. For e.g., Boron is a non-metal white the other elements are typical metals.

Oxidation states The common oxidation states of group 13 elements are +3 and + l .The stability of the + 1 oxidation state increases in the sequence Al <Ga< In <Tl, Due to Inert pair effect.

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