Concept Maps

ACYCLIC HYDROCARBONS

THE SOLID STATE

(Open chain structures containing C and H only)

CONCEPT

Class XI

Although hydrocarbons are primarily consumed in fuels, nonfuel applications of hydrocarbons are of great importance to society and the economy. Certain hydrocarbons can be found in lubricating oils, greases, solvents, fuels, wax, asphalts, cosmetics and plastics.

MAP Saturated

Unsaturated

C—C single bonds present

C—C multiple bonds present

Class XII

Alkanes General formula, CnH2n + 2

C

C

)

Alkynes (

General formula, CnH2n

C

C

Amorphous Solids

· True solids. · Anisotropic. · Have definite pattern of

Preparation

Preparation

Preparation

· From alkyl halides :

· Hydrogenation of alkynes :

· From calcium carbide : CaC2 + 2H2O Ca(OH)2 + C2H2 · Dehalogenation :

2R—Br + 2Na

Dry ether

R—R + 2NaBr

(a) R—C

(Wurtz reaction)

R—X can be converted to alkane using Zn + CH3COOH, Zn + dil. HCl, Zn–Cu + C2H5OH, LiAlH4, Zn + NaOH, NaBH4 and Ph3SnH reducing agents. · From carboxylic acids : Red P/HI

RCOOH RCH3 + H2O + I2 D 2RCOONa + NaOH Na2CO3 + RH Electrolysis

2RCOOK + 2H2O R—R + 2CO2 + H2 + 2KOH

(Kolbe’s electrolysis method)

· From carbonyl compounds : NH2NH2

RCOCH3 C H ONa R—CH2CH3 2 5

C—R¢ + H2 R R¢ C C H H

Pd/C (Lindlar’s catalyst)

(cis-alkene)

(b) R—C

C—R¢ + H2 Na/liq. NH3 R H C C or LiAlH4 R¢ H (trans-alkene)

· Dehydrohalogenation :

KOH

CH2—CH2 Br

Br

b

H alc. KOH H H—C—C—H C C a D H H (b-elimination) H X · Dehalogenation : Methanol X—CH2—CH2—X + Zn D (vic. dihalides)

CH2 CH2 + ZnX2

CH

CH

intermolecular forces into : Molecular, ionic, metallic and

CH3—C CH3—C

CH

Br

H2O

Commercial Uses

· Substitution reaction : CH3CH2CH2Cl CH3CH2CH3 Cl2 CH3—CH—CH3

· Addition of halogen :

· Alkanes : Ethane is used for making hexach loro et hane w hich is an artificial camphor. Higher alkanes in the form of gasoline, kerosene oil, diesel, lubricating oils and paraffin wax are widely used. · Alkenes : Ethene is used as a general anaesthetic. It is a starting material for a large number of compounds such as glycol, ethyl halides, ethyl alcohol, ethylene oxide, etc. · Alkynes : Acetylene is used as a general anaesthetic under the name naracylene. Acetylene is used as an illuminant.

Cl Order of reactivity : Alkanes : 3° > 2° > 1° > CH4 Halogens : F2 > Cl2 > Br2 > I2 · Oxidation : (a) Combustion or complete oxidation : CnH2n+2 + 3n + 1 O2 2 nCO2 + (n + 1)H2O + heat (b) Catalytic oxidation : 2CH4 + O2 9

:

1

Cu-tube 2CH3OH 100 atm / 473K

CH2 CH2

CCl4 CH2—Br

(Brown colour)

CH2—Br

(Colourless)

· Addition of halogen acid : CH3—CH

CH2 + HBr

Markownikoff ’s rule

Br

CH3—CH—CH3 HBr addition in presence of peroxide follows anti-Markownikoff ’s rule, known as Kharasch effect or peroxide effect. · Oxidation : CH2

alk. KMnO4 298-303 K

CH2 + H2O + O2

HO—CH2—CH2—OH

· Constituent particles are present only at the corners of the unit cell. · Consist of 7 types of arrangements with cubic as most symmetric and triclinic as least symmetric.

Cubic System

d=

Z×M g cm–3 a3 × NA

Centred Unit Cells

Constituent particles are present at the corners and at : · the centre of the unit cell (bcc) · the centre of each face of the unit cell (fcc) · the centre of any two opposite faces (End-centred)

CH3—C CH2

Properties

Isomerisation

· Isotropic. · Pseudo solids or supercooled liquids. · Do not have a definite pattern of arrangement. · Short range order. · Do not show any symmetry.

Crystal Lattice and Unit Cells

CH CCl2 4 CH3—CBr2—CHBr2

Properties

Conc. H2SO4 D

covalent solids.

liq. NH3 + 1 CH CH + Na CH CNa + H2 2 · Addition reactions : CH CH Pt/Pd/Ni CH3—CH3 H2

· Diamagnetic Substances : Substances which are weakly repelled by external magnetic field, e.g., N2, NaCl, Zn, TiO2, etc. · Paramagnetic Substances : Substances which are weakly attracted by external magnetic field, e.g., O2, Cu2+, Fe3+, Cr3+, etc. · Ferromagnetic Substances : Substances which show permanent magnetism even in the absence of external magnetic field, e.g., Ni, Fe, Co, etc. · Antiferromagnetic Substances : Substances which have zero net dipole moment even though they have large number of unpaired electrons, e.g., MnO. · Ferrimagnetic Substances : These are the substances which possess very small net magnetic moment even though they have large number of unpaired electrons, e.g., Fe3O4.

Primitive Unit Cells

· Are categorised according to

Properties

· Dehydration of alcohols :

CH2 + Br2

of symmetry. · Long range order.

(Wolff-Kishner reduction) Zn/Hg RCOCH3 conc. HCl RCH2CH3 + H2O (Clemmensen reduction)

CH2

· Exhibit plane, axis and centre

· Acidic nature :

H H

CH3CH2—OH

arrangements of atoms, ions or molecules.

CH2 CHBr

NaNH2

Classification based on Magnetic Properties

)

General formula, CnH2n – 2

MAP

SOLIDS

Classification based on Crystal Lattice Crystalline Solids

Alkenes (

CONCEPT

The solid state chemistry covers the latest advances in advanced inorganic materials with applications ranging from energy storage systems, electronic materials and sensors to the more traditional, but increasingly hi-tech materials and industries that include glass, cement and refractories.

OH CH3—C—CH3 O

Non-stoichiometric Defect

Types of Defects

Arises due to the presence of constituent particles in nonstoichiometric ratio.

Stoichiometric Defect

(Intrinsic or Thermodynamic Defect) Does not disturb the stoichiometry of solid.

Ü

Ü

It is due to missing of ions (usually cations) from the lattice sites and these occupy interstitial sites. It has no effect on the density of crystal. This is found in crystal with low coordination no. e.g., AgI, ZnS, etc.

Simple cubic 1

8×8=1

Z C. No. Relation of r, d & a Packing Efficiency

Schottky Defect Ü

Ü

Ü

It is due to equal no. of cations and anions missing from lattice sites. It results in decrease in density of crystal. This is found in the highly ionic compounds having cation and anion of same size, e.g., NaCl, CsCl, etc.

fcc

bcc 1

1

1

8 × 8+ 1 × 1 = 2 8 × 8+ 6 × 2 = 4

6

8

d a r= 2= 2

d a r= 2=2 2 a since d = 2

d 3a r= 2= 4 3a since d = 2

68%

74%

since d = a 52.4%

12

Voids

Type

Frenkel Defect Ü

Type

Octahedral Tetrahedral

Size 0.414 R 0.225 R

No. of Voids N 2N

Metal Excess Defect : Arises due to anionic vacancies, leaving a hole which is occupied by an electron thus, maintaining electrical balance. The anionic sites, occupied by unpaired electrons, are called F-centres and these impart colour to crystals. Metal Deficiency Defect : Arises when metal shows variable valency i.e., in transition metals. The defect occurs due to missing of a cation from its lattice site and the presence of the cation having higher charge in the adjacent lattice site.

BRAIN

MAP Relation between vrms , vav and vmp vrms : vav : vmp 3RT 8RT 2RT  : : M M M 8  3: : 2 ; (vrms > vav > vmp) 

KINETIC THEORY Maxwell's Law of Distribution of Velocities The distribution of molecules at different speed is given as,  m  dN  4 N   2 kT 

3/2

2

v e



mv 2 2kT dv

3 3  KE / mole   kT  NA  RT 2  2

Specific Heat Capacity

Specific Heat of a Gas At constant pressure (CP) :

Q P f  C  or C  1   R P P  2 nT At constant volume (CV) : (Q)V 1 or C  fR C  V V 2 nT Mayer’s relation : CP – CV = R (f = degree of freedom) Monoatomic Gas (f = 3) 3 3 5 5 U  RT , CV  R , C P  R,   2 2 2 3 Diatomic Gas (f = 5) 5 5 7 7 U  RT , CV  R, C P  R,   2 2 2 5 Polyatomic Gas U = (3 + f ) RT CV = (3 + f ) R CP = (4 + f ) R  = (4 + f )/(3 + f ) f  = a certain number of vibrational mode

Class XII

The average distance travelled between successive collisions of molecules of a gas is called mean free path (). 1 ; where n is the number density  2nd 2

Gold foil

Alpha particles

Detector

Source

Lead

and d is the diameter of the molecule.  While transition between different atomic levels , light radiated in various discrete frequencies are called spectral series of hydrogen atom.  Rydberg formula :   Wave number   1  R  1  1    n f 2 ni 2  R = Rydberg's constant = 1.097 × 107 m–1

Pressure Exerted by a Gas P

1 mN 2 1 2 v  v 2  E  3 V rms 3 rms 3

E = Average KE per unit volume

KINETIC THEORY

Behaviour of Gases

Law of Equipartition of Energy For any system in thermal equilibrium, the total energy is equally distributed among its various degrees of freedom and each degree 1 of freedom is associated with energy kT . 2 Gas Laws

Vander Waal's Equation For n moles of a gas, [a] = [ML5T–2] [b] = [L3]  an2   P  2  V  nb  nRT V  

8a  Critical Temperature : Tc  27 Rb a  Critical Pressure : Pc  27b2  Critical Volume : Vc = 3b

Graham's Law of Diffusion For given temperature and pressure, the rate of diffusion of gas is inversely proportional to the square root of the 1 1 density of the gas. r    M

Boyle's Laws At constant temperature, volume of a f ixed mass of a gas is invers ely proportional to its pressure. P 1 T = constant P  or PV = constant 1/V V Charle's Laws The volume of the gas is directly proportional to its absolute temperature. V V  T (at constant P) V0

t   Vt  V0 1   273 

V0 –273

0

Slope = 273 P = constant t°C

Gay-Lussac's Law Pressure of the gas varies directly with the temperature at constant volume. PT (at constant volume) t   Pt  P0 1  

273

MAP

LINE SPECTRA OF HYDROGEN Rutherford’s Model of Atom

LINE SPECTRA HYDROGEN Line Spectra OF of Hydrogen

Kinetic Theory of Ideal Gases

BRAIN

ATOMS AND NUCLEI

Mean Free Path

Kinetic Interpretation of Temperature 1 2 3 KEavg  E  mvrms  kT 2 2

Class XI

Scattering angle

1  KE of −particles K  mv 2 2  Distance of closest approach 1 2Ze 2 1 4 Ze 2 r0   . . 4 0 K 4 0 mv 2

 Impact parameter

  2 2 1 Ze cot 2 1 Ze cot 2 b  . . K 4 0 4 0 1 2 mv 2  Conclusion : An atom consists of a small and massive central core in which entire positive charge and whole mass of atom is concentrated  Drawback : The revolving electron continuously loses its energy due to centripetal acceleration and finally it should collapse into the nucleus

Alpha particle's trajectory



Impact parameter b

Nucleus

LINE Bohr’s SPECTRA OF HYDROGEN Atomic Model Electron orbits and their energy  Radius of permitted nth orbits,

n2h2

rn 

2

2

 rn  n2

4  mkZe  Velocity of electron in nth orbit, 2 kZe 2 1  vn  vn  nh n  Energy of electron in nth orbit 2 2mk 2 Z 2e 4 1  En  2 En  n2h2 n where the symbols have their usual meanings.

LINE SPECTRA OF HYDROGEN Radioactivity

LINE SPECTRA OF HYDROGEN Nuclear Reactions

 Law of radioactive decay dN  N (t ) or N (t )  N 0e t dt  Half-life ln2 0.693 T1/2      Mean life or Average life 1 T    1/2  1.44 T1/2  0.693  Fraction of nuclei left undecayed after n half lives is n t /T N 1  1  1/2    , where t  nT1/2 2 N0  2 

 Nu c l e a r f i s s i on : It i s t h e phenomenon of splitting a heavy nucleus into two or more smaller nuclei of nearly comparable masses  Nu c l e a r f u s i o n : It i s t h e phenomenon of fusing two or more lighter nuclei to form a single heavy nucleus

LINE SPECTRA OF HYDROGEN Decay Schemes  -Decay :  decay A  ZA24Y  24He  Q Z X  (Energy released)

 -Decay : 



0 1e



 ZA1Y   -Decay :

0 1e



A ZX A ZX

 ZA1Y 

 decay A * A  ZX ZX (Excited state) (Ground state)



0 0



+ Energy

ATOMS & NUCLEI

Switchyard

LINEComposition SPECTRA OF HYDROGEN and Size of Nucleus  Nucleus of an atom consists of protons and neutrons collectively called nucleons  Radius of a nucleus is proportional to its mass number as R = R0 A(1/3) (R0 = 1.2 fm)

LINE SPECTRA HYDROGEN Concept OF of Binding Energy

Control rods

Cooling tower Generator

Steam chamber

Pump Reactor

Turbine

Pump

Condenser

Cooling water

Water

LINE SPECTRA OF HYDROGEN Application of Nuclear Reactions

 The binding energy is defined as the surplus energy which the nucleons give up by virtue of their attractions when they bound together to form a nucleus Eb = [Zmp + (A – Z)mn – MN]c2  Binding energy per nucleon :
Ebn 

CONTAINMENT STRUCTURE

Eb A

A. Fission

 Uncontrolled chain reaction Principle of atomic bombs  C ontrolled chain reaction: Principle of nuclear reactors

B. Fusion

Nuclear fusion is the source of energy in the Sun and stars

PERIODICITY IN PROPERTIES

The basic object of classification is to arrange the facts regarding elements and their compounds in such a way so that we may have greatest control over their characteristics with least possible effort. The repetition of similar physical and chemical properties of elements after regular intervals is known as periodicity in properties.

CONCEPT

MAP

Periodicity in Physical Properties

Periodicity in Chemical Properties

Ionic Radius

Atomic Radius

· Across a period : The ionic radii of ions having same charge decreases as atomic number increases. · Down a group : Increases Li+ < Na+ < K+ < Rb+ < Cs+(Cations) F– < Cl– < Br– < I–(Anions) · Cationic radius < Atomic radius < Anionic radius (For isoelectronic species) · Z/e ratio increases, size decreases and vice-versa.

· Across a period : Decreases Atomic radius µ 1/Zeff Li > Be > B > C > N > O > F · Down a group : Increases H < Li < Na < K < Rb < Cs · van der Waals' radius > Metallic radius > Covalent radius

Atomic Volume

· Across a period : First decreases and then increases. Li , Be, B, C, N, O, F, Ne (cc/mol) 13 5 5 5 14 11 15 17 · Down a group : Increases Li, Na, K (cc/mol) 13 24 46 Density

· Across a period : First increases and then decreases. Na, Mg, Al, Si, P, S (g/cm3) 1.0 1.7 2.7 2.3 1.8 2.1 · Down a group : Decreases Be(1.8) , Mg(1.7) · Highest density solid : Os (22.6) · Highest density liquid : Hg (13.6) Electron Gain Enthalpy

· Across a period : More negative Li, Be, B, C, N, (kJ/mol) –60 +66 –83 –122 +31 O, F –141 –328 · Down a group : Less negative H, Li, Na, K, Rb, Cs (kJ/mol) –73 –60 –53 –48 –47 –46

Class XI

Valency

· Across a period : Increases NaH < MgH2 < AlH3 < SiH4 · Down a group : Same Reducing Nature

· Across a period : Decreases · Down a group : Increases Oxidising Nature

Electronegativity

· Across a period : Increases Li < Be < B < C < N < O < F · Down a group : Decreases H > Li > Na > K = Rb > Cs · F is most electronegative element. Ionic Character

· Across a period : First decreases and then increases. · Down a group : Increases Metallic Character

· Across a period : Decreases · Down a group : Increases Ionisation Enthalpy

· Across a period : Increases Li < Be > B < C < N > O < F · Down a group : Decreases H > Li > Na > K > Rb > Cs

· Across a period : Increases · Down a group : Decreases Strength of Oxyacids

· Across a period : Increases H3BO3 < H2CO3 < HNO3 · Down a group : Decreases HNO3 > H3PO4 > H3AsO4 Acidity of Oxides

· Across a period : Increases Na2O < MgO < Al2O3 < SiO2 < P2O5 < SO3 < Cl2O7 · Down a group : Decreases N2O3 > P2O3 Acidity of Hydrides

· Across a period : Increases CH4 < NH3 < H2O < HF · Down a group : Increases HF < HCl < HBr < HI

Melting and Boiling Points

· Across a period : M.pt. and B.pt. first increase and then decrease. Element : Na Mg Al Si P S M.pt. (K): 370.8 924 933 1693 317 392 B.pt. (K) : 1165 1396 2075 2815 557 717.6 · Down a group : They do show regular gradation but pattern of variation is different in different groups. Element : Li Na K Rb Cs M.pt. (K) : 454 370.8 335 312 302 B.pt. (K) : 1609 1165 1063 973 943

HALOGEN DERIVATIVES

The substitution of chlorine atoms into a molecule of alkane results in a compound with anaesthetic properties e.g., chloroform. Increasing the number of chlorine atoms in the compounds increases the depth of anaesthesia given but also increases toxicity. C–F bonds are very stable so their presence leads to non-flammable and unreactive properties. Organofluorine compounds find diverse applications from oil to water repellents to pharmaceuticals, refrigerants and reagents in catalysts.

Class XII

When C—X carbon is sp3 hybridised.

Allylic

Alkyl

C=C–C–X Br e.g.,

CnH2n + 1X e.g., CH3CH2CH2Cl

Methods of Preparation

(i) Direct halogenation of alkanes : Free radical mechanism : hv R — X + HX R — H + X2 ¾® Reactivity order : Allylic > 3° > 2° > 1° > CH4 (ii) Addition of HX to alkenes : CH2 = CH2 + HBr ¾® CH3CH2Br · Unsymmetrical alkenes follow Markovnikov's rule during electrophilic addition. · If the addition occurs in presence of peroxide, the product will be opposite to Markovnikov's addition (free radical mechanism). Reactivity order : HI > HBr > HCl > HF (iii) From alcohols : 3R—OH + PX3 ® 3R — X + H3PO3 R—OH + HX ¾® R — X + H2O R—OH + SOCl2 ¾® RCl + SO2­ + HCl­ [Darzen's method] (iv) Hunsdiecker reaction : CCl4 RCOOAg + Br2 ¾¾® reflux

R—Br + CO2 + AgBr (v) Finkelstein reaction : Dry acetone

R—X + NaI ¾¾¾¾® R—I + NaX (i) Dehydrohalogenation :

573 K

R—CH2CH2X ¾® R—CH=CH2

CHCl

Vinylic

Aryl

C=C–X e.g., CH2=CH–Cl

Halogen is directly attached to the carbon atom of aromatic ring, e.g., C6H5Cl

Uses of Some Commercially Important Halogen Derivatives

(i) Chloroform (CHCl3) :

– Earlier it was used as anaesthetic but due to its harmful effects it is no longer used for the purpose. – Us e d f o r p r e p a r at i o n o f chloretone and chloropicrin. – Used as a solvent for fats, waxes, rubber, resins, etc. (ii) Iodoform (CHI3) : – Used as disinfectant. – Effective as chemical antiseptic. (iii)Freons or chlorofluorocarbons : – Used as refrigerants. – Used as propellant in aerosols such as body spray, hair spray, cleansers, etc. (iv) DDT : – Used as a powerful insecticide. – Ef fective against Anopheles mosquitoes which spread malaria. (v) Teflon (–CF2–CF2–)n : – Used as non-stick coating for pans and other cookwares. – Used in containers and pipework for corrosive chemicals.

(i) Reduction : or Pd R—X + 2[H] Ni ¾¾®R—H+HX (ii) Wurtz reaction : Dry ether

2R—X + 2Na ¾¾¾® R—R + 2NaX (iii)Reaction with metals : Dry ether

R—X + Mg ¾¾¾® R—MgX (Powder)

(Grignard reagent) Ether

2R—X + 2Zn ¾¾® R2Zn + ZnX2 Dry ether

4C2H5Br + 4Pb/Na ¾¾® (C2H5)4Pb sod. lead alloy

Tetraethyl lead

+ 4NaBr + 3Pb (iv) Corey-House reaction : R2CuLi + R¢X ¾® R—R¢ + R–Cu + LiX (This reaction can be used to prepare unsymmetrical alkanes.) (v) Oxidation : O DMSO

R—CH2X ¾¾® R—C—H 1° Alkyl halide

Aldehyde

X

O DMSO

R—CH—R ¾¾® R—C—R 2° Alkyl halide

Ketone

Chemical Properties Elimination Reactions

Nucleophilic Substitution Reactions

Miscellaneous Reactions

SN1

SN2

· First order kinetics · Reactivity : 3° > 2° > 1° > CH3X

· Second order kinetics · Reactivity : CH3X > 1° > 2° > 3°

(I) Hydrolysis with alkalies : RX + AgOH ¾® ROH + AgX (moist) aq. R — X ¾¾® R—OH + KX KOH

(ii) Williamson's synthesis : Heat

R – X + NaOR¢ ¾¾® ROR¢ + NaX alc. (iii)R—X + KCN ¾® KX + RCN C H OH/H O

2 5 2 (iv) R—X + AgCN ¾¾¾¾® R—N ® C D

H3O+ conc. HCl Na/C2H5OH or LiAlH4 SnCl2/HCl

H O+

3 RCONH2 ¾¾¾® conc. HCl

RCOOH + NH3 R — CH2NH2 R — CH = NH×HCl ¾®

alc. KOH R—CH2—CH2—X ¾¾¾® R—CH=CH2 – Elimination follows the Saytzeff 's rule. – Ease of dehydrohalogenation : Tertiary > Secondary > Primary (ii) Action of heat :

Benzylic

CH3

MAP

When C—X carbon is sp2 hybridised.

Halogen Derivatives

C6H5CH2X e.g.,

CONCEPT

H3O+

R—CHO + NH4Cl

THE p-BLOCK ELEMENTS (Group 13)

CONCEPT

Atomic and Physical Properties

B2O3

· Oxidation States : +1 and +3 B,

Al, Ga, In, Tl Metals

Ga In Tl

Group 13 is the first group to span the dividing line between metals and non-metals and its chemistry is more diverse than that of groups 1 and 2.

· Reactivity towards air : Ø 4E + 3O2

· Electronic configuration : [Noble gas]ns2np1

Metalloid

Al

Chemical Properties

· Elements : B, Al, Ga, In, Tl

· Metallic Character :

B

Ø 2E + N2

D

2E2O3 (E = Group 13 elements)

Al2O3

Ga2O3 Amphoteric

Acidic D

In2O3

Tl2O

Basic

2EN (Except Ga, In, Tl) · Reactivity towards acids : Ø B reacts only with strong oxidising acids at high temperature.

· Atomic radii, ionic radii, density and stability of +1 oxidation state : Generally increase down the group however, the atomic radius of Ga is lower than that of Al. · Boiling points and stability of +3 oxidation state : Decrease down the group. · Electronegativity : First decreases from B to Al then increases from Al to Ga and then decreases marginally down the group. · Melting points : Decrease from B to Ga and then increase. · Ionisation energy : B > Tl > Ga > Al > In · Lewis acids : BCl3, AlCl3 etc. behave as Lewis acids due to incomplete octet. · Complex formation : Due to small size, high charge density and availability of vacant d-orbitals.

B + 3HNO3

conc. H2SO4 D

H3BO3 + 3NO2

Ø All other elements react with both, non-oxidising and oxidising acids liberating H2 gas. Ø Al becomes passive with conc. HNO3 due to the formation of a thin protective layer

of its oxide (Al2O3) on the surface of the metal which prevents it from further action. · Reactivity towards alkalies : Ø 2B + 6KOH

> 773 K

2 K3BO3 + 3H2

2Na+ [E(OH)4]– + 3H2 (E = Al, Ga) · Reactivity towards halogens : 2EX3 (Except TlI3) Ø 2E + 3X2 (X = F, Cl, Br, I)

Ø 2E + 2NaOH + 6H2O

Anomalous Behaviour of Boron · Difference in behaviour of B is due to small size, high ionisation energy and absence of d-orbitals. · B is extremely hard having high m.pt and b.pt. · B shows maximum covalency of 4 while rest of the elements show maximum covalency of 6. · B exhibits allotropy. · B for ms on ly cova lent compounds.

GROUP 13 : THE BORON FAMILY

Important Compounds of Boron

· Preparation :

Diborane (B2H6)

Ø Laboratory method :

Borax (Na2[B4O5(OH)4].8H2O) · Preparation : D Ø Ca2B6O11 + 2Na2CO3 Na2B4O7 + 2NaBO2 + 2CaCO3 Ø 4H3BO3 + Na2CO3   Na2B4O7 + 6H2O + CO2 · Properties : Ø White crystalline solid. Ø Na2B4O7 + 7H2O   2NaOH + 4H3BO3 Ø Na2B4O7 . 10H2O   D Na2B4O7   D 2NaBO2+ B2O3 Borax bead

Diglyme

Ø Industrial method : 450 K

2BF3 + 6NaH B2H6 + 6NaF · Properties : Ø Colourless, highly toxic gas. Ø B2H6 + 3O2   B2O3 + 3H2O Ø B2H6 + 6H2O   2B(OH)3 + 6H2 D Ø 3B2H6 + 6NH3   3[BH2(NH3)2]+ [BH4]– 2B3N3H6 + 12H2 Borazine · Structure : Ø Four bonds : 2 centre-2 electron type Ø Two bonds : 3 centre-2 electron type (banana bonds)

H

B

HBO2 + H2O Metaboric acid Red heat 410 K 4HBO2 –H O H2B4O7 2B2O3 + H2O 2 Boron Tetraboric trioxide acid

O

H

B

H

O

H 3c

OH

B

OH

en tre

H

- 2 electron

nd

O

O O B B O

370 K

H

B

d on

O B

H3BO3

- 2 electron re b H nt

OH Na2 HO

B2H6 + 2NaI + H2

3c e

Sodium metaborate

2NaBH4 + I2

Orthoboric acid (H3BO3) · Preparation : Ø Na2B4O7 + 2HCl + 5H2O   2NaCl + 4H3BO3 · Properties : Ø White crystalline solid with a soapy touch. Ø Planar BO33– units joined by H-bonds to form layer structure of boric acid. Ø Monobasic acid : B(OH)3 + 2H2O   [B(OH)4]– + H3O+

bo

H

O

B

H O H

O

O

H

H

O

O B

H

O

H

O

H

H O B O H

PERIODICITY IN PROPERTIES

The basic object of classification is to arrange the facts regarding elements and their compounds in such a way so that we may have greatest control over their characteristics with least possible effort. The repetition of similar physical and chemical properties of elements after regular intervals is known as periodicity in properties.

CONCEPT

MAP

Periodicity in Physical Properties

Periodicity in Chemical Properties

Ionic Radius

Atomic Radius

· Across a period : The ionic radii of ions having same charge decreases as atomic number increases. · Down a group : Increases Li+ < Na+ < K+ < Rb+ < Cs+(Cations) F– < Cl– < Br– < I–(Anions) · Cationic radius < Atomic radius < Anionic radius (For isoelectronic species) · Z/e ratio increases, size decreases and vice-versa.

· Across a period : Decreases Atomic radius µ 1/Zeff Li > Be > B > C > N > O > F · Down a group : Increases H < Li < Na < K < Rb < Cs · van der Waals' radius > Metallic radius > Covalent radius

Atomic Volume

· Across a period : First decreases and then increases. Li , Be, B, C, N, O, F, Ne (cc/mol) 13 5 5 5 14 11 15 17 · Down a group : Increases Li, Na, K (cc/mol) 13 24 46 Density

· Across a period : First increases and then decreases. Na, Mg, Al, Si, P, S (g/cm3) 1.0 1.7 2.7 2.3 1.8 2.1 · Down a group : Decreases Be(1.8) , Mg(1.7) · Highest density solid : Os (22.6) · Highest density liquid : Hg (13.6) Electron Gain Enthalpy

· Across a period : More negative Li, Be, B, C, N, (kJ/mol) –60 +66 –83 –122 +31 O, F –141 –328 · Down a group : Less negative H, Li, Na, K, Rb, Cs (kJ/mol) –73 –60 –53 –48 –47 –46

Class XI

Valency

· Across a period : Increases NaH < MgH2 < AlH3 < SiH4 · Down a group : Same Reducing Nature

· Across a period : Decreases · Down a group : Increases Oxidising Nature

Electronegativity

· Across a period : Increases Li < Be < B < C < N < O < F · Down a group : Decreases H > Li > Na > K = Rb > Cs · F is most electronegative element. Ionic Character

· Across a period : First decreases and then increases. · Down a group : Increases Metallic Character

· Across a period : Decreases · Down a group : Increases Ionisation Enthalpy

· Across a period : Increases Li < Be > B < C < N > O < F · Down a group : Decreases H > Li > Na > K > Rb > Cs

· Across a period : Increases · Down a group : Decreases Strength of Oxyacids

· Across a period : Increases H3BO3 < H2CO3 < HNO3 · Down a group : Decreases HNO3 > H3PO4 > H3AsO4 Acidity of Oxides

· Across a period : Increases Na2O < MgO < Al2O3 < SiO2 < P2O5 < SO3 < Cl2O7 · Down a group : Decreases N2O3 > P2O3 Acidity of Hydrides

· Across a period : Increases CH4 < NH3 < H2O < HF · Down a group : Increases HF < HCl < HBr < HI

Melting and Boiling Points

· Across a period : M.pt. and B.pt. first increase and then decrease. Element : Na Mg Al Si P S M.pt. (K): 370.8 924 933 1693 317 392 B.pt. (K) : 1165 1396 2075 2815 557 717.6 · Down a group : They do show regular gradation but pattern of variation is different in different groups. Element : Li Na K Rb Cs M.pt. (K) : 454 370.8 335 312 302 B.pt. (K) : 1609 1165 1063 973 943

HALOGEN DERIVATIVES

The substitution of chlorine atoms into a molecule of alkane results in a compound with anaesthetic properties e.g., chloroform. Increasing the number of chlorine atoms in the compounds increases the depth of anaesthesia given but also increases toxicity. C–F bonds are very stable so their presence leads to non-flammable and unreactive properties. Organofluorine compounds find diverse applications from oil to water repellents to pharmaceuticals, refrigerants and reagents in catalysts.

Class XII

When C—X carbon is sp3 hybridised.

Allylic

Alkyl

C=C–C–X Br e.g.,

CnH2n + 1X e.g., CH3CH2CH2Cl

Methods of Preparation

(i) Direct halogenation of alkanes : Free radical mechanism : hv R — X + HX R — H + X2 ¾® Reactivity order : Allylic > 3° > 2° > 1° > CH4 (ii) Addition of HX to alkenes : CH2 = CH2 + HBr ¾® CH3CH2Br · Unsymmetrical alkenes follow Markovnikov's rule during electrophilic addition. · If the addition occurs in presence of peroxide, the product will be opposite to Markovnikov's addition (free radical mechanism). Reactivity order : HI > HBr > HCl > HF (iii) From alcohols : 3R—OH + PX3 ® 3R — X + H3PO3 R—OH + HX ¾® R — X + H2O R—OH + SOCl2 ¾® RCl + SO2­ + HCl­ [Darzen's method] (iv) Hunsdiecker reaction : CCl4 RCOOAg + Br2 ¾¾® reflux

R—Br + CO2 + AgBr (v) Finkelstein reaction : Dry acetone

R—X + NaI ¾¾¾¾® R—I + NaX (i) Dehydrohalogenation :

573 K

R—CH2CH2X ¾® R—CH=CH2

CHCl

Vinylic

Aryl

C=C–X e.g., CH2=CH–Cl

Halogen is directly attached to the carbon atom of aromatic ring, e.g., C6H5Cl

Uses of Some Commercially Important Halogen Derivatives

(i) Chloroform (CHCl3) :

– Earlier it was used as anaesthetic but due to its harmful effects it is no longer used for the purpose. – Us e d f o r p r e p a r at i o n o f chloretone and chloropicrin. – Used as a solvent for fats, waxes, rubber, resins, etc. (ii) Iodoform (CHI3) : – Used as disinfectant. – Effective as chemical antiseptic. (iii)Freons or chlorofluorocarbons : – Used as refrigerants. – Used as propellant in aerosols such as body spray, hair spray, cleansers, etc. (iv) DDT : – Used as a powerful insecticide. – Ef fective against Anopheles mosquitoes which spread malaria. (v) Teflon (–CF2–CF2–)n : – Used as non-stick coating for pans and other cookwares. – Used in containers and pipework for corrosive chemicals.

(i) Reduction : or Pd R—X + 2[H] Ni ¾¾®R—H+HX (ii) Wurtz reaction : Dry ether

2R—X + 2Na ¾¾¾® R—R + 2NaX (iii)Reaction with metals : Dry ether

R—X + Mg ¾¾¾® R—MgX (Powder)

(Grignard reagent) Ether

2R—X + 2Zn ¾¾® R2Zn + ZnX2 Dry ether

4C2H5Br + 4Pb/Na ¾¾® (C2H5)4Pb sod. lead alloy

Tetraethyl lead

+ 4NaBr + 3Pb (iv) Corey-House reaction : R2CuLi + R¢X ¾® R—R¢ + R–Cu + LiX (This reaction can be used to prepare unsymmetrical alkanes.) (v) Oxidation : O DMSO

R—CH2X ¾¾® R—C—H 1° Alkyl halide

Aldehyde

X

O DMSO

R—CH—R ¾¾® R—C—R 2° Alkyl halide

Ketone

Chemical Properties Elimination Reactions

Nucleophilic Substitution Reactions

Miscellaneous Reactions

SN1

SN2

· First order kinetics · Reactivity : 3° > 2° > 1° > CH3X

· Second order kinetics · Reactivity : CH3X > 1° > 2° > 3°

(I) Hydrolysis with alkalies : RX + AgOH ¾® ROH + AgX (moist) aq. R — X ¾¾® R—OH + KX KOH

(ii) Williamson's synthesis : Heat

R – X + NaOR¢ ¾¾® ROR¢ + NaX alc. (iii)R—X + KCN ¾® KX + RCN C H OH/H O

2 5 2 (iv) R—X + AgCN ¾¾¾¾® R—N ® C D

H3O+ conc. HCl Na/C2H5OH or LiAlH4 SnCl2/HCl

H O+

3 RCONH2 ¾¾¾® conc. HCl

RCOOH + NH3 R — CH2NH2 R — CH = NH×HCl ¾®

alc. KOH R—CH2—CH2—X ¾¾¾® R—CH=CH2 – Elimination follows the Saytzeff 's rule. – Ease of dehydrohalogenation : Tertiary > Secondary > Primary (ii) Action of heat :

Benzylic

CH3

MAP

When C—X carbon is sp2 hybridised.

Halogen Derivatives

C6H5CH2X e.g.,

CONCEPT

H3O+

R—CHO + NH4Cl

SOME BASIC CONCEPTS OF CHEMISTRY

CONCEPT

Class XI

Mole concept is the centre of quantitative calculations in chemistry and the multiple interpretations of this concept allow us to bridge the gap between the submicroscopic world of atoms and molecules and the macroscopic world that we can observe.

MAP

REACTION KINETICS

Class XII

CONCEPT

Apart from playing an important role in industries and study of biological processes, kinetics also plays a role in environmental and atmospheric chemistry as part of an effort to understand a variety of issues ranging from the fate of prescription pharmaceutical in waste water to cascade of reactions involved in the ozone cycle.

MAP

Mole Concept

e

le Mo

g rid

B

n g of atoms n g of molecules

¸m

ol.

ma

ss i

ng

Instantaneous Rate

Mass (g)

23

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2 6.0

10

Mole

Gas volume (dm3) ¸ molar volume

olu

e

l

Rate Law/Rate Equation The expression of rate in terms of molar concentration of reactants. For reaction, aA + bB cC + dD Rate = k[A]x[B]y Where, k = rate constant or specific reaction rate. Depends only upon temperature.

l

Unit of k =

l

olu

×v

e

lum

lum

× vo

¸v

me

¸ mol. mass in g

me

(dm

(dm

3

)

3

)

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Empirical and Molecular Formula Change to

Atomic ratio Simplest ratio = minimum atomic ratio

Change to

Empirical formula

Simple whole number ratio = Simplest ratio × integer Multiply with n

Molecular formula

Stoichiometric Calculations Limiting Reagent l

l

l

The limiting reagent or reactant is the reactant that limits the amount of the other reactant that can combine and the amount of product that can form in a chemical reaction. The excess reagent is the substance that is not used up completely in a reaction. For example, in combustion of 12 g of carbon in excess of oxygen (i.e., more than 32 g of oxygen), carbon acts as the limiting reagent.

l

t1/2 (half-life) =

Reactions in Solutions l

Mass %

l

Molarity (M) =

[R]0 k = –slope

where, n = order of reaction. Order of Reaction Sum of powers of concentration terms in the rate law expression. e.g., Rate = k[A][B]2 \ Order = 1 + 2 = 3 l For n th order, l

l

l

Rate = k[R] or

l

Unit of k = s–1 t1/2 = 0.693/k In terms of pressure,

l

ln[R]0 k = –slope

Normality (N) =

l

Molality (m) =

l

Mole fraction, x2 =

l

l

and x1 =

l

[R]

Useful Relations for First Order Reaction

t75% = 2t1/2, t87.5% = 3t1/2 ,t93.75% = 4t1/2, t96.87% = 5t1/2, t99.9% = 10t1/2

Effect of Catalyst on Activation Energy A catalyst increases the rate of reaction by providing a path of lower activation energy. Reaction path without catalyst

Second Order Reaction l l l

Rate = k[R]2 or 1/[R]t = kt + 1/[R]0 Unit of k = L mol–1 s–1 t1/2 = 1/k[R]0

Ea

Ea

Reactants

Reaction path with catalyst Energy of reaction

Products Reaction coordinate

nth l

Activation Energy (Ea) Energy required by the reactant molecules for effective collisions to form products. l The slope of ln k vs 1/T has the value –Ea/R and is used to calculate value of Ea. l

l

t

Experimental concept and can be zero or fractional. Depends upon pressure and temperature. Molecularity of Reaction The number of molecules of reactants taking part in elementary step of a reaction. Theoretical concept and can never be zero or fractional. Independent of pressure and temperature.

Arrhenius Equation k = Ae–Ea/RT Here, A = pre-exponential factor R = Gas constant Ea = Activation energy

[R]

l

l

l

l

t

First Order Reaction

× mol. mass in g

% age Atomic ratio = At. mass

Unit of k = mol L –1s –1

Average Rate

× molar volume

¸ vo

Density (g dm–3)

l

Number of particles

23

.02

×6

× mol. mass in g

%Composition

Zero Order Reaction Rate = k or kt = [R]0 – [R]

0

1 3×

¸ ¸ mol. mass in g

Differential Rate Equation aA + bB cC + dD

l

Dependency of Rate on Temperature

Potential energy

l

Change in concentration of reactants or products as function of time (Unit : mol L–1 s–1 or M s–1)

Rate

l

Integrated Rate Equation

Rate of Reaction

Rate

l

Have a Look! Contrary to belief of chemistry students, 'Avagadros' number was not discovered by Amadeo Avagadro. It is just an honorary name. First time number of molecules in any substance was calculated in 1865, by Josef Loschmidt. (2.6 × 1019 molecules in one cm3 of a gaseous substance). Term Avagadros' number was used by Jean Baptiste Perrin in 1909. The unit 'mole' was introduced in 1900 by Ostwald and defined this unit in terms of gram.

[R]

l

l

ln[R]

l

1 mole = NA particles = 6.023 × 1023 particles. A mole is defined as the amount of substance that contains the same number of entities (atoms, molecules, ions or other particles), as the number of atoms present in12 g of the C-12 isotope. The number of atoms present in 12 g of C-12 is equal to 6.023 × 1023.

¸ atomic mass (g)

l

l

Order Reaction

Rate = k[R]n or (n – 1)kt =

l

Unit of k = (mol L–1)1–n s–1

l

t1/2 = 2n–1 – 1 / k(n – 1)[R]0

n–1

Temperature Coefficient It is the ratio of k 298 to k308. l For ever y 10° rise in temperature the rate becomes double. l

Collision Theory Rate = P×ZABe –Ea /RT

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DETECTION OF ORGANIC FUNCTIONAL GROUPS

CONCEPT

Functional groups are the specific groups of atoms within molecules that have characteristic properties regardless of the other atoms present in a molecule. The identification of functional groups and the ability to predict reactivity based on functional group properties is one of the cornerstones of organic chemistry.

Class XII

MAP

Detection of functional group Detection of carbonyl group

Detection of unsaturation Baeyer's or KMnO4 test

Ester test

Br2 - CCl4 test

2KMnO4 2H2O

Red brown

Disappearance of purple colour.

Ceric ammonium nitrate test

Fruity smell (can also be used to detect –COOH group)

Disappearance of brown colour. Iodoform test R–CO– CH3 + 3I2 + 4NaOH

Detection of alcoholic group

2ROH + (NH4)2[Ce(NO3)6] [(ROH)2.Ce(NO3)4] red colour

+ 2NH4NO3

Ketonic group Brady's reagent (2, 4-DNP) test

NaHSO3 test

3NaI + CHI3 Yellow ppt.

+ RCOONa + 3H2O Formation of yellow ppt. of CHI3 (for methyl ketones only).

Sodium nitroprusside test Sodium nitroprusside solution + NaOH + RCOR Appearance of wine-red colour.

Aldehydic group

Schiff 's test Schiff ’s reagent + 2R CHO (Colourless)

Deep red or violet colour complex

Fehling's test Benedict's test RCHO + 2Cu(OH)2 + NaOH RCHO + 2Cu2+ + 5OH– RCOONa + Cu2O + 3H2O 2Cu+ + RCOO– + 3H2O Mulliken Barker test

NaHCO3 test RCOOH + NaHCO3 RCOONa + H2O + CO2 Brisk effervescence of CO2 indicates –COOH group.

Detection of amino group

Litmus test Blue litmus paper turns red. –COOH group may be present.

Zn + NH4Cl

RNO2 + 4[H] RNHOH + H2O RNHOH + 2[Ag(NH3)2]OH RNO + 2H2O + 4NH3 + 2Ag Grey black ppt.

Carbylamine test

Nitrous acid test

R – NH2 + CHCl3 + 3KOH R – N C + 3KCl + 3H2O

R – NH2 + HNO2 R – OH + N2 + H2O N2 effervescence indicates 1° amino group.

Isocyanide

Liebermann's nitroso test (

)

(yellow oily)

FeCl3 test FeCl3 + 6C6H5OH – [Fe(OC6H5)6]3 + 3H+ + 3HCl Violet

Detection of nitro group Ferrous hydroxide test RNO2 + 6Fe(OH)2 + 4H2O Light green

Primary amine

Offensive smell of isocyanide indicates 1° aliphatic or aromatic amino group.

Secondary amine

Silver mirror

Red ppt.

Red ppt.

Detection of carboxylic group

Tollens' test RCHO + 2[Ag(NH3)2]OH RCOONH4 + 3NH3 + H2O + 2Ag(s)

RNH2+ 6Fe(OH)3 Brown ppt.

Detection of phenolic group

Azo dye test pH 9-10 C6H5N+2Cl–+ C6H5OH 0-5°C

p-Hydroxyazobenzene

(Formation of orange or red dye)