The P-BOCK ELEMENTS - Lecture Notes

P BLOCK ANOMALOUS PROPERTY OF B AND C Boron and Carbon (1st elements in 13th and 14th group) show different property from other elements in their group due to Small size Absence of d orbital High electronegativity ATOMIC AND PHYSICAL PROPERTIES Atomic size B < Al > Ga < In < Tl Atomic size increases from Boron to Aluminium as expected due to increase in size but expected increase in size is not observed from Ga onwards because effective nuclear charge increases due to poor shielding effect as inner electrons present in d and f orbital. Electronegativity B > Al < Ga < In < Tl Electronegativity decreases from Boron to Aluminium as expected due to increase in size thereafter electronegativity increases because atomic size does not show expected increase due to poor shielding effect of inner d and f electrons. Density B < Al < Ga < In < Tl Generally density increases down the group as increase in mass is more than increase in volume. From Ga onwards density shows a large increase as atomic size does not show expected increase. Melting point Boron has an usually high value because it is a smaller atom with icosohedral structure with 12 atoms in 1 unit . Gallium is having an unusually low melting at 30°C because in the solid structure of Ga , each Ga atom is NOT bonded equally with neighbouring atoms and exist as Ga2 units.Since gallium

is available as a liquid over a wide range of temperature it is used in as a thermometric liquid for reading high temperature. Oxidation state Group 13 elements has a configuration of ns2np1 so they show oxidation state of +1 and +3 but down the group stability of +3 oxidation state decreased due to inert pair effect i.e. due to increase in effective nuclear charge down the group ns2 electron experience stronger attraction hence does not participate in bonding. Hence +1 oxidation become stable. B and Al show +3 oxidation state Ga and In show both +1 and +3 oxidation state hence they undergo disproportionation in +1 oxidation state. Tl prefer +1 oxidation state +3 is possible but less stable hence undergo reduction to +1 act as oxidizing agent. Halides Boron form covalent halides of formula BX3 with trigonal planar shape, sp2 hybridization. Thermal stability BF3 > BCl3 > BBr3 > BI3 as the size of halogen increase bond becomes weaker and stability decreases. Lewis acidity – all Boron halides are Lewis acidic due to availability vacant orbital and shortage of two electrons. The correct order of Lewis acidity BF3 < BCl3 < BBr3 < BI3 In BF3 the Lewis acidity is less because electron deficiency is compensated to an extend by back bonding (filled orbital of fluorine overlap with vacant orbital of B). As size of halogen increase back bonding decrease and Lewis acid increase. Aluminium halides AlF3 is ionic, all other Aluminium halides are covalent . AlCl3 in solid state, vapour and non polar solvent exist as dimer through coordinate bond to attain octet configuration. In aqueous state exist as ionic compound. [Al(H2O)6]3+ + HCl as hydration energy provide ionisation energy for the formation of Al3+

Ga and In form monohalides and trihalides. Tl form TlX and TlX3 but TlX3 halides are less stable due to inert pair effect and Tl(III)I3 does not exist but Tl+I3- exist. Diborane The simplest hydride BH3 cannot exist due to electron deficiency so it exist as a dimer B2H6. B2H6 contain four 2c-2e bond with H atoms and two 3c-2e bond with two H atoms. 2c-2e bond is shorter and stronger than 3c-2e bond. Boron atom is sp3 hybridized and the molecule has 3D structure with two B atoms and 2c-2e H atoms in one plane and 3c-2e H in a perpendicular plane. PREPARATION: BF3 + NaH B2H6 + NaH BCl3 + LiAlH4 B2H6 + LiCl + AlCl3 NaBH4 + I2 B2H6 + NaI + I2 Reaction: B2H6 + NH3 B2H6. 2NH3 2000C B3N3H6 Borozine ( Inorganic benzene) B2H6 + NH3(excess) (BN)x Inorganic graphite B2H6 + O2 B2O3 + H2O B2H6 + H2O B(OH)3 + H2O

B2H6 + NaH NaBH4 . 8H2O Borax ( Na2B4O7.10H2O) Structure 2Na+ In borax two boron atoms are sp2 hybridized and two other boron atoms are sp3 hybridized. Two H2O molecules are bonded to Boron atoms as -OH and 8H2O molecules exist as water of crystallization. Hydrolysis Na2B4O7 H2O NaOH + H3BO3 Borax is a salt of weak tetraboric acid and strong base NaOH so it undergo salt hydrolysis to form an alkaline solution. Effect of heating Borax on heating becomes anhydrous and on further heating form a glassy bead of NaBO2 and B2O3. Na2B4O7.10H2O Na2B4O7 NaBO2 + B2O3 The transparent glassy bead on heating with transition metal oxides forms corresponding colored metal meta boride from which metal can be identified and thus is known as borax bead test. Preparation CaCO3 + Na2B4O7 + NaBO2 1. From colemanite Na2B4O7 + H2O + CO2 Ca2B5O11 + Na2CO3 2. From boric acid H3BO3 + Na2CO3

Orthoboric acid ( H3BO4) In Orthoboric acid B is sp2 hybridized and has a trigonal planar shape, each molecule are involved in intermolecular hydrogen bond to form a planar sheet like structure. It exists as a crystalline solid soluble in hot water. Acidic Character B(OH)3 + NaOH B(OH)4- Orthoboric acid act as a weak monobasic Lewis acid due to the presence of vacant “p” orbital. Since the above neutralization is reversible a sharp end point is not obtained hence the above reaction is carried out in presence of cis-diol (glucose, glycerol, glycol etc.) Effect of heat H3BO3 1000C HBO3 1600C H2B4O7 2B2O3 When orthoboric acid is heated it undergoes dehydration to form metaboric acid , tetraboric acid, and finally B2O3.

Reaction with Ethanol Orthoboric acid reacts with ethanol to form volatile triethyl borate which burns with green edged flame. Hence the reaction is used as a test. B(OH)3 + C2H50H B(OC2H5)3 Preparation 1. Na2B4O7(aq) + H2SO4 Na2SO4 + H3BO3 Aqueous solution of borax on acidification form H3BO3 2. Ca2B5O11 + SO2 Ca(HSO3)2 + H3BO3 REACTION OF GROUP 13 ELEMENTS Reaction with air Amorphous Boron and Aluminium reacts with oxygen present in air to form oxide on heating and forms nitride with nitrogen. B + O2 B2O3 Al + O2 Al2O3 B + N2 BN Al + N2 AlN Ga, In and Tl will not form nitride. Reaction with water B, Ga, In will not react with water, Al reacts with water on heating to form Al(OH)3 liberating H2. Al + H2O Al(OH)3 + H2 Tl reacts with O2 in moist condition to form Tl(OH). Reaction with acid B reacts with oxidizing acid like conc HNO3 to form H3BO3 and does not react with other acids, B + conc HNO3 H3BO3 + NO2

Other elements in group 13 reacts with acid forming corresponding salts liberating H2. Al + HCl AlCl3 + H2 However Al is rendered passive by conc HNO3 due to the formation of oxide layer, since HNO3 is a strong oxidizing agent. Reaction with alkali Boron being non metallic for acidic oxide reacts with alkali on heating forming borate. B + KOH K3BO3 + H2 Al and Ga form amphoteric oxide reacts with alkali to form aluminate and gallate liberating H2. Reaction with carbon Boron and Aluminium reacts with carbon to form carbide on heating. B+C B4C ( Norbide) Al + C Al4C3 Reaction with metals Boron being non metallic reacts with metals to form borides on heating. Mg + B Mg3B2 All other elements being metallic form alloys with other metals.

GROUP 14 ELEMENTS Allotropes of Carbon Phenomenon by which an element exist in different forms. Crystalline allotropes – Diamond , Graphite , Fullerene Amorphous – Charcoal, Lampblack , Coal DIAMOND GRAPHITE 1. Each carbon bonded to 4 other Each C bonded to 3 other carbon carbon Sp2 hybridized. 2 Sp3 hybridized. 3 3 dimensional tetrahedral 2-D dimensional hexagonal planar network so strong to have hard structure sheet like structure in which 2 structure. sheets are bonded by wanderwals force of attraction. 4 Better conductor of heat due to interlinking. Bad conductor because the heat can’t be transferred due to wanderwals force of attraction. 5 No free electron so bad conductor Strong bond due to ������ bond[ very strong of electricity. bond] 6 C-C single bond. Partially double bond. 7 Chemically inactive. Chemically active . Graphite react with oxidizing agent 8 Less strong bond( long bond No free electron to ������ bond. length) 9 Very hard. Soft 10 Enthalpy at formation is non zero. Thermodynamically stable form of graphite because bond strength is very strong. So enthalpy of formation is zero 11 Cutting and abrasive. Lubricating agent 12 Jewellery [1 carat= 200mg] . Graphite – lubricating agent, carbon fibres. Uses: Diamond – cutting , abrasive.

Fullerene When a graphite is heated using a electric arch or using laser in presence of a inert gas[if air it react to form CO2] it will be vapourized to form black rock which on condensation form fullerene[C60 and C70] C60 – Buckminster Fullerene It is a football like structure made of 60 carbon with hexagonal rings(20) and pentagonal rings(12) arrangement with each carbon of sp2 hybridized( so ������ bond will be there). Bond is strong so it is used as lubricating agent. TIN It has two allotropes grey tin ( β ) and white tin (α).White tin change to grey tin at low temperature(300C).Grey tin is brittle this is referred as tin plague. OXIDES Group 14 elements form 2 types of oxides MO and MO2 OXIDES OF CARBON Carbon form three oxides CO, CO2 and C3O2 CARBON MONOXIDE Carbon monoxide is poisonous because it combines with iron in hemoglobin and forms carboxyhemoglobin. CO is neutral. PREPARATION OF CO

• When air is passed through a mixture of heated coke a mixture of CO and N2(producer gas) is obtained C+ air CO + N2 • When steam is passed through a mixture of heated coke a mixture of CO and H2 (water gas) is obtained C+ H2O CO + H2 • When hydrocarbon undergo incomplete combustion CO is obtained CH4+O2 CO + H2O • When boric acid is subjected to dehydration using P2O5 carbon monoxide is obtained HCOOH + P2O5 CO • When K4[Fe(CN)6] K2SO4 + FeSO4 + (NH4)SO4+CO+H2O H2SO4 ➢ CO is a powerful reducing agent. Hence it is used for extraction of metals. It is also cheap. Fe2O3 + CO Fe + CO2 ZnO + CO Zn +CO2 ➢ Reaction with chlorine CO + Cl2 COCl2 CO reacts with chlorine phosgene. ➢ Mond’s process CO used in Mond’s process for purification of Ni Ni (impure) + CO Ni(CO) 4 Ni(pure) + 4CO Nickel tetracarbonyl ➢ CO which is neutral react with NaOH only at high temperature and pressure to form sodium formate which on acidification gives formic acid. CO + NaOH HCOONa HCOOH

CARBON DIOXIDE ➢ Colorless, Odourless , non poisonous gas. ➢ It’s inhaling causes suffocation called Asphyxia. ➢ A mixture of CO2 and O2 is known as carbogen. ➢ Preparation: 1. By the complete combustion of carbon or hydrocarbon. C + O2 CO2 CH4 + O2 CO2 2. CaCO3 HCl CaCl2 + CO2 + H2O NaHCO3 HCl NaCl + CO2 +H2O By treating carbonate or bicarbonate with mineral acid CO2 will be evolved. 3. When carbonates and bicarbonates are heated they decompose to give CO2 except those of Na, K, Rb, Cs, Fr because their monoxide are not stable so CO2 will not be formed[ If monoxide is formed then only we get CO2]. But Li being a smaller size can form monoxide[ Bigger cation can only stabilize bigger anion and smaller cation can only stabilize smaller anion]. ➢ NaHCO3 HCl NaCl + CO2 +H2O This reaction is used in baking industries and in fire extinguishers because CO2 will not undergo combustion as it is heavy gas, not inflammable and CO2 being stable do not give O2. PROPERTIES ➢ CO2 is acidic in nature. ➢ CO2 + H2O H2CO3 Carbonic acid As H2CO3 obtained by dissolving CO2 in blood along with bicarbonate( HCO3-) act as a buffer which help in maintaining the pH of 7.8 in blood.[ If more than maximum amount then it can’t stabilize] ➢ CO2 react with ammonia CO2 +2NH3 NH4COONH2 NH2CONH2 Ammonium carbonate Urea CO2 being acidic react with ammonia which is basic to give ammonium carbonate which on heating gives urea which is a fertilizer . DRY ICE ➢ Solid CO2. ➢ Provide a cooling effect without wetting because it is sublimeable produce vapour [ But it is more good than using ice because there is no wetness]. Dry ice will cause burns because it takes heat from our body.

➢ CO2 is a greenhouse gas. It absorbs heat and radiations and keep the earth warm. SUBOXIDE[C3O2] ➢ It is acidic. ➢ It is obtained by the dehydration of Malonic acid. COOH CH4 P2O5 C3O2 COOH O=C=C=C=O sp hybridized OXIDES OF SILICON Silicon dioxide is a high melting solid. CO2 exist as a gas because carbon being the topmost member can form p������-p������ bond .So it form 2������ and 2σ bonds with O2 and become stable. So between two CO2 molecules there us only wander waals force of attraction which is weak. So it act as a gas O=C=O. But in case of Si it can’t form ������ bond. So it form bond with other molecules to satisfy its 4 bonds 1 valency and form a tetrahedral network structure which is solid. O Si O O Si O O Si O SiO2 exhibits polymorphism.[ it is phenomenon in which compounds exist in different forms]. It can be crystalline or amorphous . It’s forms are quartz, trichymite, cristoballite – crystalline forms. Amorphous forms – Kieselguhr, silica gel. SiO2 is acidic in nature but it is chemically in active because of strong Si-O. Therefore it is used in glass making. SiO2 being acidic react with basic NaOH to form sodium silicate. SiO2 + NaOH Na2SiO3( ) ( In burette if we take base the above reaction and it form Na2SiO3 . So the knob will get stuck)

Reaction with HF SiO2 + HF SiF4 Because of this reaction HF can’t be stored in glass . This reaction can be used for heching of glass. Silicon will not form monoxide others will form monoxide. Si can only form covalent bonds as it can’t form ������ bonds all others can form ionic bonds. SiO require high temperature so it can’t form at normal condition. SILICATES Naturally occurring compounds of silicon which contains SiO44- tetrahedra as the basic structural unit Type of silicate General formula No.of oxygen shared Orthosilicate SiO44- Nil Pyrosilicate Si2O76- 1 Chain silicate (SiO3)n2n- 2 Cyclic silicate (SiO3)n2n- 2 Sheet silicate (Si2O5)n2n- 3 3D silicate 4 SiO2 SILICONES Organo silicon polymers with Si-O bonds having a general formula (R2SiO)n RCl + Si Cu RSiCl3 + R2SiCl2 +R3SiCl 570 R2SiCl2 H2O R2Si(OH)2 Silicones are formed by the condensation of organo silicon hydroxides.

RSiCl3 is used to prepare crosslinked silicon and R3SiCl is used to stop polymerization. Silicones are thermally stable, less volatile, water repelling, chemically inert, maintain elasticity and viscosity over a range of temperature and electrical insulators. ZEOLITES Sodium aluminium silicates are known as zeolites. These are 3D silicates in which few Si4+atoms are replaced by Al3+ and residual charge balanced by Na+. Zeolites have a porous structure hence used as shape selective catalyst and for removing hardness of water by ion exchange.