p- Block Elements

Fullerenes

This was discoved in 1985. The real name of Fullerene is buckminster fullerene. Fullerene is third allotrope form of carbon material after graphite and diamond whose molecule consists of 20 hexagonal and 12 pentagonal rings as the basis of an icosohedral symmetry closed cage structure. Each carbon atom is bonded to three others and is sp2 hybridised.
The most stable and common of fullerenes is the C₆₀ molecule. C₆₀ molecule has two bond lengths - the 6:6 ring bonds can be considered "double bonds" and are shorter than the 6:5 bonds. C₆₀ is not "superaromatic" as it tends to avoid double bonds in the pentagonal rings, resulting in poor electron delocalisation. As a result, C₆₀ behaves like an electron deficient alkene, and reacts readily with electron rich species. Fullerene is harder than diamond. Also, the ductility is 100 times stronger than steel. Fullerene has amazing electrical conductivity and has more stronger conductivity than copper. Fullere's weighs only 1/6th of copper material. The geodesic and electronic bonding factors in the structure account for the stability of the molecule. Theoratically, an infinite number of fullerenes can exist, their structure based on pentagonal and hexagonal rings, constructed according to rules for making icosahedra.
USES:
One of the most important uses of Fullerene is medicine.
Fullerenes are active molecules.
Fullerene molecule can be used as an antioxidant because it can easily react with radicals due to the high affinity of the electron.
It is used as an anti-aging and anti-damage agent in the cosmetic sector.
Fullerenes are used as antiviral agents. This use is provided by its unique molecular structure, antioxidant effect and biological compatibility.
May be used for osteoporosis treatment because of its preferential localization.

Inert Pair Effect

The reluctance of two ns-electrons to take part in bond formation due to the high energy needed for unpairing them is called inert pair effect. This was proposed by Sidgwick.
Some p-block elements, such as thullium(Tl), polonium(Po), tin( Sn ), lead(Pb), bismuth( Bi ) etc exhibit Inert pair effect. The '5s' electron of tin and '6s' electrons of lead and bismuth have a tendency to remain inert due to inert pair effect.
From their electronic arrangement, we see that these elements contain inner 'd' or 'f' electrons and due to poor shielding effect of 'd' or 'f' orbitals, the effective nuclear charge on outer most 's'-electrons act strongly. So, the nucleus pull the 's'-electrons strongly. Consequently, these two 's'-electrons show a less tendency to participate in chemical reaction and these two 's'-electrons remain inert.

Consequences of Inert Pair Effect

# Due to inert pair effect, many physical and chemical properties of the relating elements become changes.
SnCl₂ is more stable than SnCl₄ because, in the formation of SnCl₂, 'Sn' metal utilize two '5p'-electrons only. While, in the formation of SnCl₄, 'Sn' metal used both '5s' and '5p' electrons. But, '5s' electron of 'Sn' is not available for formation of molecule due to inert pair effect. Hence, SnCl₄ becomes unstable.
# Inert pair effect cause the variable valency of elements.
Sn & Pb shows +2 & +4 oxidation states while Tl shows +3 & +1 oxidation state due to inert pair effect.
# Inert pair effect, affect melting and boiling point of elements. For example, the melting and boiling point of 'Po' is less than that of 'Te'. Generally, the melting and boiling point of elements increase down the group.
Now, 'Po'-element contain maximum number of 'd' and 'f' electrons. So, the inert pair effect becomes more effective for 'Po' than 'Te'. As a result, the '6s'-electron of 'Po' is less available than '5s'-electron of 'Te'. Hence, in case of Po, the inter-atomic Vander waal's force of attraction is less than Te. Consequently, the melting and boiling point of Po is less than Te.
# Inert pair effect, influence the oxidizing and reducing properties of compounds. For example, +5 oxidation state of Bi is less stable than +3 oxidation state. Due to this, BiF₅ act as a strong oxidizing agent. It oxidized the other reducing substance readily, and changes it's oxidation state from +5 to more stable +3.

Structure of Peroxydisulphuric Acid

Peroxydisulfuric acid is the inorganic compound with the chemical formula H₂S₂O₈ also called Marshall's acid after its inventor Professor Hugh Marshall. Oxidation state of Sulfur is +6. It is a powerful oxidizing agents.

Which is more acidic H₂SO₄ or H₂SO₃ ?

The oxidation state of S is +6 in H₂SO₄ and +4 in H₂SO₃. Greater is the oxidation number of central atom, more it attracts the electrons towards itself and also, more it stabilises the conjugate base. So, H₂SO₄ is stronger acid than H₂SO₃

Borazine or Borazole (Inorganic Benzene)

Borazine, also known as borazole, is a polar inorganic compound with the chemical formula B₃N₃H₆. The compound is isoelectronic and isostructural with benzene. For this reason borazine is sometimes referred to as “inorganic benzene.
Preparation:
When B₂H₆ and NH₃ in the ratio of 1:3 are heated borazole is obtained.
                  B₂H₆ + 6NH₃ -----> 2B₃N₃H₆ + 12H₂

Properties of Borazine

1. It is colorless liquid
2. It shows unsaturated reaction.
                  B₃N₃H₆ + 3HCl → B₃N₃H₉Cl₃
                  B₃N₃H₆ + 3Br₂ → B₃N₃H₆Br₆
                  B₃N₃H₆ + 3H₂O → B₃N₃H₁₂O₃
3. It forms two series of methyl derivatives-
a. N- methyl derivatives
b. B- methyl derivatives
4. It is isoelectronic with benzene.
5. When borazine is pyrolysed above 340°C, B₃N₆H₁₀ and B₅N₅H₈ are produced. These products are boron- nitrogen analogues of diphenyl and naphthalene respectively.
6. Borazine gets slowly hydrolysed by water to produce boric acid, ammonia and Hydrogen.Hydrolysis is favoured by the increase in temperature.
                  B₃N₃H₆ + H₂O -----> H₃BO₃ + NH₃ + H₂

Struture of Borazine

In Borazine both Boron and Nitrogen are sp² hybridised. Each N-atom has one lone pair of electrons, while each B-atom has an empty p-orbital. (B-N) bond in borazine is a Dative bond, which arises from the sidewise overlapping between the filled p-orbitals of N-atom and empty p-orbitals of B-atom. In this cyclic compound, the three BH units and three NH units are alternate to each-other.
                          

Preparation and Preperties of Diborane

Preparation of Diborane

1. It is prepared by the action of H₃PO₄ on Mg-boride-
                  H₃PO₄ + Mg₃B₂ = B₂H₆ + Mg₃(PO₄)₂
2. When BF₃ is reduced by sodium borohydride or LiH, diborane is formed.
                  4BF₃ + 3NaBH₄ = 2B₂H₆ + 3NaBF₄

Properties of Diborane

Physical Propeeties:
* It is air sensitive, volatile and reactive gas with repelling smell.
* It is fairly stable in absence of moisture and grease.

Chemical Propeeties of Diborane

1. Reaction with dry HCl: it react with dry HCl in presence of Al₂X₆, forms B₂H₅Cl
                  B₂H₆ + HCl = B₂H₅Cl + H₂
2. Reaction with concentrated KOH solution:
With concentrated KOH solution, it forms potassium hypoborite.
                  B₂H₆ + 2KOH = K₂(BH₂OH)₂ + H₂

3. Hydrolysis: On hydrolysis, diborane forms boric acid.
                  B₂H₆ + 6H₂O = 2H₃BO₃ + 6H₂

4. Burn in Air: It burns in air release large amount of heat.
                  B₂H₆ + 3O₂ = B₂O₃ + 3 H₂O

5. Reaction with chlorine: it violently react with chlorine.
                  B₂H₆ + 6Cl₂ = 2BCl₃ + 6HCl

6. Reaction with Ammonia:
Diborane react with ammonia but the product is depend upon the experimental condition.
                  B₂H₆ + 2NH₃ ---L.T.----> B₂H₆.2NH₃
                  B₂H₆ + 2NH₃ ---H.T.---->2BN + 6H₂
                  3B₂H₆ + 6NH₃ ---H.T.---->2B₃N₃H₆+ 12H2

Why diamond is a non-conductor and graphite fairly a good conductor of electricity ?

In diamond, unit cell is tetrahedral. Each carbon atom is sp³ hybridized and forms four sigma bonds with four other carbon atoms and this trend extends throughout the crystal. All the four electrons of each carbon atom are tightly bound in these covalent bonds. As a result, no free electron are available in diamond so it is a nonconductor of heat and electricity.
However, in Graphite, each carbon atom is sp² hybridized and bonded to three neighbor carbon atoms so one of its four valance electrons is relatively free to move along the layers. Hence, graphite is a conductor parallel to the layers and non-conductor perpendicular to the layer.

Why PbCl₂ is ionic but PbCl₄ is fairly covalent compound ?

When a metal forms more than one halide, the halides in which metal has lower oxidation state tends to be ionic while that in higher oxidation state is covalent. Similarly, high polarizing power of Pb⁺⁴ as compare to Pb⁺² makes PbCl₂ mainly ionic but, PbCl₄ fairly covalent.

Sulphur forms SF₄ and SF₆ but oxygen does not form OF₄ and OF₆ why ?

Due to absence of d-orbitals in the valence shell, oxygen cannot show an oxidation state of +4 and +6 and hence does not form OF₄ and OF₆.
However, S contains d-orbitals in the valence shell and hence can show a maximum oxidation state of +6. Since F₂ is a very strong oxidising agent, it oxidises sulphur to its higher oxidation state of +4 and +6 and thus forms SF₄ and SF₆.