p-Block Elements Chemistry Notes

→ Those elements, in which the last electron enter in subshell, are known as p-block elements. These p-block elements belongs to six main groups from 13 to 18 of the extended or long form of the periodic table. These elements are located at the extreme right of the periodic table. The general electronic configuration of these elements is ns² np^1-6 but helium has 1s².

→ In other words, we can say that. in these elements the s-subshell is completely filled while the electron enters in p-subshell of valence shell. So the valence shell configuration of these elements changes from ns² np¹ to ns² np⁶. The properties of these elements are depend upon the electrons present in p.orbitals. The groups of p.block are regarded by some typical names.

They are as follows:

Group 13 ( B to TI) – Boron family
Group 14 (C to Pb) – Carbon family
Group 15 (N to Bi) – Nitrogen family or Pnicogens
Group 16 (0 to Po) – Oxygen family or chalcogens
Group 17 (F to At) – Halogens
Group 18 ( He to Rn) – Inert gases or Noble gases

→ Except intert gases (which are chemically very less reactive) all other elements of this block are very reactive. This is the only block in the periodic table which includes all the three types of elements i.e.. metals, non-metals and semi-metals or metalloids. s-block elements and pb1ock elements are also known as representative elements. We have already discussed the chemistry of the elements of group 13 and 14 in class XI. Therefore, this unit includes the chemistry of the elements of group 15-18.

Chapter in Brief and Glossary :

→ Phosphorus, arsenic and antimony all exist as discrete tetratomic tetrahedral molecules i.e., P₄, As₄ and Sb₄ because these elements cannot from multipie bonds. In these molecules each at’om is bonded to three atoms by single covalent bond and the angle between them is 60° due to the presence of lone pair of electron.

→ Phosphours exist in various allotropic forms i,e. white, red and black phosphorus, the yellow or white allotropic form of phosphorus is very reactive and poisonous in nature. It readily catches lire when exposed in air. It cause phossy jaw disease White phosphorus is stored into water.

Some properties of hydrides of group – 15 are as follows

NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃ (Bask character)
NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃ (Bond Angle)
NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃ (Thermal Stability)
NH₃ < PH₃ < ASH₃ < SbH₃ < BiH₃ (Reducing Nature)

→ The important oxo acids of phosphorus are H₃PO₄ (orthophosphoric acid), H₃ PO₂ (hypophoaphorus acid). H₃PO₃(phosphorus acid). HPO₃ (mcta phosphoric acid. H₄P₂O₆ (hypophorphoric acid) and H₄P₂O₇ (pyrophosphonc acid). The basicity of these oxo acids is decided by the presence of – OH group.

p-Block Elements Chemistry Notes 1

→ Phosphorus can form two types of chloride i.e., PCl₃ and PCl₅, PCl₃ has a pyramidal shape and sp hybridisation while PCl₅ has triangular bipyramidal shape and si’d hybridization. PCl₅ has two types of P—Cl bonds Le., axial and equatorial. Axial bonds become longer than equatorial bonds to minimise the lone pair bond pair repulsion present in molecule. PCl₅ in solid state. exists as ionic compound. [PCl₅]⁺ [PCl₆]^–

→ Group — 16 has five elements i.e., O, S, Se, Te and Po. The general electronic configuration of these elements is na² np⁴. They show maximum oxidation state + 6. They are collectively called as chalcogens (ore forming).

→ In laboratory, oxygen can be prepared by heating KClO₃ in presence of MnO₂. Oxygen is a gas while other elements are oiId st room tempreture. Oxygen molecule is diatomic. It has one and one it bond while sulphur exist as staggered 8.atom rings.

→ All the elements of group – 16 rrirm hydrides of the type H₂M where M O, S, SO, To, PO. H₂O is liquid due to the tendency of t’romation of H-bonding while other hydrides of group — l6are poisonous gases with pungent smell, Some important properties of these hydrides are as follows

H₂O > H₂O> S > H₂Se > HeTe (Thermal st.ability)
H₂O < H₂S < H₂Se < HeTe (Reducing character)
H₂O < H₂S < H₂Se > H₂Te (Volatility)
H₂O < H₂S < H₂Se < H₂Te (Acidic behaviour)
H₂S < H₂Se < H₂Te < H₂O (Bond angle)
H₂O < H₂S < H₂Se < H₂Te (Covalent character)
H₂S < H₂Se < HeTe < H₂O (m.p. and b.p.)

→ Sulphur forms various oxyacids like H₂SO₄ (Sulphuric avid). H₂SO₃ (Suiphurous acid), H₂S₂O₈ (Peroxodisulphuric acid), H₂S₂O₇ (Perusulphuric acid). Among these oxyacida H₂SO₄ is very important. It is a strong dibasic acid. It is known as ‘oil of vitriol’. It can be prepared by Contact process.

→ Halogens are very reactive elements. Their reactivity decreases down the group Halogen mok’culcs have low dissociation energies. Fluorine due to greater lone pair-lone pair repulsion have lower bond dissociation energy than chlorine.
F₂ < Cl₂ < Br₂ < I₂ (Bond dissociation energy)

→ All the halogen form hydrides with hydrogen. They form volatile covalent hydride of fornnila HX. HF is liquid due to formation of hydrogen bonding while other are gases. Their properties are as follows

HF > HCl > HBr > HI (Thermal stability)
HF < HCl < HBr < Hl (Acidic strength)
HCl < HBr < HI < HF (Boiling Point)

→ Fluorine due to very high electronegativity and small size form only one oxuacid (HOF) while other halogens forms ozo acids of th type HXO, HXO₂, HXO₃ and HXO₄.

→ In the oxo acids ot’ same halogen, the acidic nature and thermal stability increases while oxidising nature decreases with increase in oxidation number.

HClO < HClO₂ < HClO₃ <HClO₄ (Acidic behaviour)
ClO^– < ClO₂^– < ClO₃^– < ClO₄^– (Thermal stability)
HClO < HClO₂ < HClO₃ < HClO₄ (Oxidising nature)

For different halogens,

HClO > HBrO > HIO (Acidic strength)
HClO > HBrO > HIO (Thcrmal stability)