The p-Block Elements Class 11 Notes - Chapter 11

According to the CBSE Syllabus 2023-24, this chapter has been removed from NCERT Class 11 Chemistry textbook.

In the periodic table, there are six groups of p-block elements from 13 to 18 with an electronic configuration ns²np^1–6. It has all types of elements such as metalloids, non-metal, and metal. Their chemical and physical properties are highly influenced by the difference between the inner core of their electronic configuration. The lighter elements of the group have a quite stable group oxidation state. The heavier elements form dπ–dπ or dπ–pπ bonds and have more stable lower oxidation states. Whereas the lighter elements form pπ–pπ bonds. The absence of d orbital in second-period elements has limited their maximum covalence to 4, while heavier ones can exceed this limit.

Group 13 Elements: The Boron Family

• Group Members-boron (B), gallium (Ga), indium (In), aluminium (Al) & thallium (Tl).
• Example of a typical non-metal is Boron and the other members are metals.

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Electron Deficiency in Boron Compounds

An example of a typical non-metal is boron. A fairly rare element, Boron mainly occurs as orthoboric acid, (H₃BO₃), borax, Na₂B₄O₇·10H₂O, and kernite, Na₂B₄O₇·4H₂O. Covalent bond formation by using four orbitals (2px, 2s, 2py, 2pz) with the convenience of 3 valence electrons 2s²2p¹ leads to the electron deficiency in boron compounds. Due to this deficiency, they are a good electron acceptor and therefore behave as Lewis acids. Boranes are formed when boron and dihydrogen form a covalent molecular compound. One simple example is diborane which contains 2 bridging hydrogen atoms between 2 boron atoms.

Some examples of compounds of boron-containing dioxygen are borax and boric acid.

• Boric acid – a weak monobasic acid that acts as Lewis acid by accepting electrons from hydroxyl ion.
• Borax – a white crystalline solid. The borax bead test gives characteristic colours of transition metals.

Few Important Questions

1. Explain why boron trifluoride behaves like a Lewis acid.
2. Excessive content of CO₂ is responsible for global warming. How?
3. Justify the amphoteric nature of aluminium by writing the reactions.
4. Why do white fumes appear around the bottle of anhydrous aluminium chloride? State a reason.
5. Explain why Boron is unable to form BF₆^3– ion?
6. Diamond is covalent, yet it has a high melting point. Why?
7. What are silicones ?

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