The p-Block Elements Class 11 Notes - Chapter 11

In the periodic table, there are six groups of p-block elements from 13 to 18 with an electronic configuration ns2np1–6. 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 BF63– ion?
  6. Diamond is covalent, yet it has a high melting point. Why?
  7. What are silicones ?

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