RBSE Class 11 Chemistry Notes Chapter 11 The p-Block Elements

These comprehensive RBSE Class 11 Chemistry Notes Chapter 11 The p-Block Elements will give a brief overview of all the concepts.

RBSE Class 11 Chemistry Chapter 11 Notes The p-Block Elements

→ p-block Elements: p-block of periodic table is unique in terms of having all types of elements-metals, non-metals and metalloids.

→ Electronic Configuration: There are six groups of p-block elements in the periodic table numbering from 13 to 18. Their valence shell electronic configuration is ns2np1-6 (except for He).

→ Oxidation State: In addition to the group oxidation state, these elements show other oxidation states differing from the total number of valence electrons by unit of two.

→ Absence of d-orbitals: Absence of d-orbital in second period elements limits their maximum covalence, to 4 while heavier ones can exceed this limit.

→ Boron Group: Boron is a typical non-metal and the other members are metals. The availability of 3 valetice electrons (2s² 2P¹) for covalent bond formation using four orbitals (2s, 2px, 2py and 2pz) leads to the so called electron deficiency in boron compounds. This deficiency makes them good electron acceptor and thus boron compounds behave as Lewis acids.

→ Boron forms covalent molecular compounds with dihydrogen as boranes, the simplest of which is diborane, B₂H₆. Diborane contains two bridging hydrogen atoms between two boron atoms; these bridge bonds are considered to be three-centre two-electron bonds. The important compounds of boron with dioxygen are boric acid and borax.

→ Borax: The borax bead test gives characteristic colours to the transition metals.

→ Carbon: Carbon is found both in free and combined state. The purest form of carbon are diamond and graphite found in free state and in combined state, it is found in the form of carbonates, natural gas, in petroleum, and in all living organism.

→ Carbon is a typical non-metal forming covalent bonds employing all its four valence electrons (2s² 2p²). It shows the property of catenation, the ability to form chains or rings, not only with C—C single bonds but also with multiple bonds (C=C or C=C).

→ The tendency to catenation decreases as C > Si > Ge ~ Sn > Pb.

→ Carbon provides one of the best examples of allotropy. Three important allotropes of carbon are diamond, graphite and fullerenes.

→ The members of the carbon family mainly exhibit +4. and +2 oxidation states; compounds in +4 oxidation states are generally covalent in nature. The tendency to show +2 oxidation state increases among heavier elements.

→ Carbon forms two important oxides: CO and C0₂. Carbon monoxide is neutral whereas C0₂ is acidic in nature.

→ Carbon monoxide having lone pair of electrons on C forms metal carbonyls. It is deadly poisonous due to higher stability of its haemoglobin
complex as compared to that of oxyhaemoglobin complex. Carbon dioxide as such is- not toxic. However, increased content of CO₂ in atmosphere due to combustion of fossil fuels and decomposition of limestone is feared to cause increase in ‘green house effect’. This, id turn, raises the temperature of the atmosphere and causes serious complications.

→ Silica, silicates and silicones are important class of compounds and find applications in industry and technology.

→ Boric acid:

• It is obtained by Borax, Boron trichloride and diborane.
• It has a layered structure in which B (OH)₃ units are joined by hydrogen bonds,
• It is a weak basic acid and gives red wine colour with litmus paper.

→ Diborane: It is known as dimer of BH₃. It can be prepared by NaBH₄, BF₃ and NAH.

→ In diborane, banana bond is present.

→ Graphite: It has a layered structure. These layers are joined together by weak Vander waals forces. Therefore, graphite is soft and slippery. Carbon is in sp² hybridised state. It is a good conductor of electricity.

→ Diamond: Carbon is in sp³ hybridised state. It is bad conductor of electricity and is very hard.

→ Fullerene: It is a large molecule in the shape of a soccer ball, containing 60 carbon atoms, whose structure is the shape of a truncated icosahedron (a hollow, spherical object with 32 faces, 12 of them pentagons and the rest hexagons).

→ Photosynthesis: The process by which green plants and some other organisms use sunlight to synthesize nutrients from carbon dioxide and water. Photosynthesis in plants generally involves the green pigment chlorophyll and generates oxygen as a by-product.
6 C0₂ + 6 H₂O → C₆H₁₂O₆ + 6O₂

→ Green House Effect: Carbon dioxide has a tendency to absorb heat radiated by earth causing the atmosphere of earth warm. This increases temperature of earth. This is known as green house effect.

→ Silicon Dioxide: Commonly known as silica. Silicon dioxide is a covalent, three dimensional network solid in which each silicon atom is covalently bonded in a tetrahedral manner to four oxygen atoms. Each oxygen atom in turn covalently bonded to another silicon atoms.

→ Quartz is extensively used as a piezoelectric material. It has made possible to develop extremely accurate clocks, modern radio and television broadcasting and mobile radio communications.

→ Silicon Tetrachloride: Preparation: ,

• Silicon tetrachloride may be made by passing chlorine over a heated mixture of silica and carbon:
• By passing dry chlorine on hot silicon.

→ Zeolites: If aluminium atoms replace few silicon atoms in three-dimensional network of silicon dioxide, overall structure known as aluminosilicate, acquires a negative charge. Cations such as Na⁺, K⁺ or Ca²⁺ balance the negative charge. Examples are feldspar and zeolites.

→ Silicones: They are a group of organosilicon polymers, which have (R₂SiO) as a repeating unit. These are hydrophobic in nature.

→ Silicates: A large number of silicates minerals exist in nature. Some of the examples are feldspar, zeolites, mica and asbestos. The basic structural unit of silicates is SiO₄ in which silicon atom is bonded to four oxygen atoms in tetrahedron fashion. In silicates either the discrete unit is present or a number of such units are joined together via corners by sharing 1, 2, 3 or 4 oxygen atoms per silicate units.