CBSE Class 11 Chemistry The P Block Elements Notes Set A

 Subject: Chemistry

Class: XI

Chapter: The p-Block Elements

Top concepts

1. Elements in which the last electron enters the p-subshell of their outermost energy level are called p-block elements. The elements belonging to groups 13 to 18 constitute p-block elements.

2. General electronic configuration for elements belonging to p-block is ns²np^1-6

3. General characteristics of p-block elements

 2. Metallic and non-metallic character: Elements which show characteristics of both metals and non-metals and are called metalloids. Common metalloids in p-block elements are Si, Ge, As, Sb, Te, Po, At.

3. Differences in behaviour of first element of each group:

(a)Covalence upto four: First member of each group belongs to second period elements and have only four valence orbitals i.e., one 2s and three 2p orbitals. They do not have vacant d-orbitals in their valence shell. Therefore each member has maximum covalence of four (using one 2s and three 2p orbitals).Next members belonging to third or higher periods have vacant d-orbitals. For example elements of third period of p-block with the electronic configuration 3s² 3p^x has vacant 3d-orbitals lying between 3p and 4s energy levels. Therefore, they can easily expand their octets and can show covalence above four. For example:

(i) Boron forms only BF^-₄(coordination number of B is four) whereas aluminium forms AlF³6 (coordination number of Al is six). 

(ii) Carbon can form only tetrahalides (CX₄, X = F, Cl, Br, I) whereas other members can form hexahalides, SF₆,  SiCl^2-₆ etc. 

(iii) Nitrogen forms only NF₃ while phosphorous forms pentahalides like PCl₅, PF₅ etc. 

(iv) Fluorine does not form FCl₃ (F has more than octet) while chlorine forms (Cl has extended octet) 3 ClF

(b)Reactivity: Elements of second period do not have d – orbitals and are less reactive as compared to elements of third period which have d – orbitals .For example tetrahalides of carbon are not hydrolysed by water whereas tetrahalides of other elements of group 14 are readily hydrolysed (for e.g. Si)

(c)Tendency to form multiple bonds: Because of combined effect of smaller size and availability of p – orbitals, the first member of each group shows greater tendency to form pπ – pπ multiple bonds either with itself (such as C = C, C ≡ C, N ≡ N, O = O) or with other members of the second period of elements (such as C = O, C ≡ N, N = O, etc.). Heavier elements of the group do not have strong tendency to form this type of pπ- pπ bonding. The heavier elements do form π - bonding but they but they involve d – orbitals and form dπ – pπ or dπ – dπ bonding.

5. Group 13 Elements: The Boron family

1. Electronic Configurations: Elements of group 13 have the general outer electronic configuration of ns²np1

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