Class 11
Class 12
Focus
📊 Periodic Classification - Trends & Orders
Atomic Radius - Across Period
Decreases left to right: nuclear charge increases, electrons added to same shell, greater attraction. Li (152) > Be (112) > B (85) > C (77) > N (75) > O (73) > F (72) pm
Atomic Radius - Down Group
Increases down group: new electron shell added each period. Li (152) < Na (186) < K (227) < Rb (248) < Cs (265) pm
EXCEPTION: Ga < Al
Gallium (135 pm) smaller than Aluminium (143 pm) due to d-block contraction. Poor shielding by 3d electrons increases effective nuclear charge.
Ionic Radius - Cations
Cations smaller than parent atom (electron loss). Higher charge = smaller: Na+ (95) > Mg2+ (65) > Al3+ (50) pm. Isoelectronic series: radius ∝ 1/Z
Ionic Radius - Anions
Anions larger than parent atom (electron gain). O2- (140) > F- (133) > Na+ (95) > Mg2+ (65) pm for isoelectronic (10e-) series.
Ionization Enthalpy Trend
Increases across period, decreases down group. More energy to remove e- from smaller, higher Zeff atoms.
EXCEPTION: Be > B
Beryllium IE1 (899 kJ/mol) > Boron (801). Be: 1s2 2s2 (full s stable). B: 1s2 2s2 2p1 (easier to remove p electron).
EXCEPTION: N > O
Nitrogen IE1 (1402) > Oxygen (1314). N: 1s2 2s2 2p3 (half-filled p stable). O: 1s2 2s2 2p4 (removing gives half-filled).
IE1 Order Period 2
Li (520) < B (801) < Be (899) < C (1086) < O (1314) < N (1402) < F (1681) < Ne (2081) kJ/mol. Note Be>B and N>O exceptions.
Successive IE Jump
Large jump when removing from stable configuration or inner shell. Na: IE1=496, IE2=4562 (removing from Ne core). Mg: IE2=1451, IE3=7733.
Electron Gain Enthalpy
Becomes more negative across period (more exothermic). Cl (-349) > F (-328) > Br (-325) > I (-295) kJ/mol. F less than Cl due to small size e- repulsion.
EXCEPTION: Positive EGE
Be, Mg, N, noble gases have positive electron gain enthalpy (endothermic). Stable configurations (full s, half-filled p, full shell) resist adding electron.
Electronegativity Trend
Increases across period, decreases down group. F (4.0) > O (3.5) > N (3.0) = Cl (3.0) > Br (2.8) > I (2.5) = S (2.5) = C (2.5) > H (2.1)
Metallic Character
Increases down group, decreases across period. Left/bottom = metals, right/top = non-metals, middle = metalloids (B, Si, Ge, As, Sb, Te).
Lanthanoid Contraction Effect
4f electrons poor shielding, Zeff increases across lanthanoids. Causes 5d elements (Hf, Ta, W) similar size to 4d (Zr, Nb, Mo). Affects properties.
🔗 Chemical Bonding
Fajans Rules - Covalent Character
Small cation + large anion + high charge = more covalent. Polarizing power ∝ charge/radius. Order covalent character: LiCl < NaCl < KCl (increasing ionic)
Lattice Energy
U ∝ (q+ × q-)/(r+ + r-). Higher charge, smaller ions = higher LE. MgO (3795) > NaCl (787) kJ/mol. Determines MP, hardness, solubility.
VSEPR - 2 Electron Pairs
Linear, 180°. Examples: BeCl2, CO2, C2H2, HgCl2. sp hybridization.
VSEPR - 3 Electron Pairs
Trigonal planar, 120°. BF3, CO32-, NO3-, SO3. sp2 hybridization.
VSEPR - 4 Pairs (Tetrahedral)
109.5°. CH4, CCl4, NH4+, SO42-. sp3 hybridization.
VSEPR - 4 Pairs (Pyramidal)
~107°. NH3, PCl3, H3O+. One lone pair, sp3. Bond angle <109.5° due to lp-bp repulsion.
VSEPR - 4 Pairs (Bent)
~104.5°. H2O, H2S, OF2. Two lone pairs, sp3. Bond angle further reduced.
VSEPR - 5 Pairs
Trigonal bipyramidal. PCl5, PF5. sp3d. Axial bonds longer than equatorial.
VSEPR - 6 Pairs
Octahedral, 90°. SF6, [Co(NH3)6]3+. sp3d2 hybridization.
MOT - Bond Order
BO = (Nb - Na)/2. N2: BO=3, diamagnetic. O2: BO=2, paramagnetic (2 unpaired). O2+ BO=2.5, O2- BO=1.5, O22- BO=1.
Hydrogen Bonding Strength
HF > H2O > NH3 (based on EN). Affects boiling points: H2O (100°C) > HF (19.5°C) due to network vs dimer. Increases BP, MP, viscosity.
Dipole Moment Order
HF (1.91D) > HCl (1.03D) > HBr (0.79D) > HI (0.38D). Decreases down group despite EN decrease because bond length increases more.
🧪 p-Block Elements (Class 11 - Groups 13-14)
Inert Pair Effect
ns2 electrons reluctant to participate for heavier elements. Tl+ > Tl3+, Pb2+ > Pb4+, Bi3+ > Bi5+ stable. Increases down group.
Diborane Structure B2H6
2 bridging H atoms with 3-center-2-electron bonds (banana bonds). 4 terminal B-H (2c-2e), 2 bridge B-H-B (3c-2e). Each B sp3 hybridized.
Boron Anomalous
B differs from Al: only covalent (no B3+), max covalency 4 (no d orbitals), B2O3 acidic, Al2O3 amphoteric, BH3 dimerizes, forms electron-deficient compounds.
Carbon vs Silicon
C: strong catenation, multiple bonds, CO2 gas linear O=C=O. Si: weak catenation, no pπ-pπ, SiO2 solid network (each Si tetrahedral to 4 O). Due to size and bond strength.
Allotropes of Carbon
Diamond: sp3, tetrahedral network, hardest, insulator. Graphite: sp2, layered, hexagonal rings, conducts (delocalized e-), lubricant. Fullerene C60: sp2, soccer ball.
⚗️ Coordination Compounds
Werner Theory
Primary valency = oxidation state (ionizable, non-directional). Secondary valency = coordination number (directional, fixed geometry). [Co(NH3)6]Cl3: primary=3, secondary=6.
Spectrochemical Series
I- < Br- < SCN- (S) < Cl- < S2- < F- < OH- < C2O42- < H2O < NCS- (N) < CH3CN < py < NH3 < en < bipy < phen < NO2- < PPh3 < CN- < CO. Weak to strong field.
CFSE Octahedral
Δo splitting: t2g lower (-0.4Δo each), eg higher (+0.6Δo). CFSE = (-0.4nt2g + 0.6neg)Δo. Strong field: low spin (pair e-). Weak field: high spin (max unpaired).
CFSE Examples
[Fe(H2O)6]3+ d5 weak: t2g3 eg2, CFSE=0, μ=5.92 BM high spin. [Fe(CN)6]3- d5 strong: t2g5 eg0, CFSE=-2.0Δo, μ=1.73 BM low spin.
Magnetic Moment
Spin-only: μ = √n(n+2) BM. n=1→1.73, n=2→2.83, n=3→3.87, n=4→4.90, n=5→5.92 BM. Used to determine unpaired electrons and geometry.
Geometrical Isomerism
MA4B2 octahedral: cis (90°) and trans (180°). MA3B3: fac (facial, 3 same on one face) and mer (meridional, 3 in plane). Square planar MA2B2: cis/trans.
Optical Isomerism
[M(AA)3] where AA=bidentate: [Co(en)3]3+, [Cr(ox)3]3- show optical isomerism. [M(AA)2B2] cis is optically active, trans is not. No plane of symmetry.
VBT - [Fe(CN)6]4-
Fe2+ d6, CN- strong field → pairing, d2sp3 hybridization, octahedral, diamagnetic (low spin), inner orbital complex.
VBT - [FeF6]3-
Fe3+ d5, F- weak field → no pairing, sp3d2 hybridization, octahedral, paramagnetic (5 unpaired, high spin), outer orbital complex.
🧬 p-Block Elements (Class 12 - Groups 15-18)
N2 vs P4 Reactivity
N≡N bond very strong (941 kJ/mol), N2 inert. P-P single bond weak (213 kJ/mol), P4 tetrahedral highly reactive. N2 gas, P4 solid.
Brown Ring Test
NO3- + FeSO4 + conc H2SO4 → brown ring [Fe(H2O)5NO]2+ at junction. Confirms nitrate. NO reduces Fe3+ to Fe2+ then complexes.
PCl3 and PCl5
PCl3: pyramidal sp3, hydrolyzes to H3PO3. PCl5: trigonal bipyramidal sp3d (gas), in solid [PCl4]+[PCl6]-. Hydrolyzes to POCl3 then H3PO4.
Oxoacids of Phosphorus
H3PO2 (hypophosphorous) monobasic +1 reducing. H3PO3 (phosphorous) dibasic +3 reducing. H3PO4 (phosphoric) tribasic +5. Basicity = number of OH groups attached to P.
Ozone Structure
O3 bent, 117° angle, resonance hybrid, bond order 1.5, O-O 128 pm (longer than O=O 121 pm). Powerful oxidizing agent, bent sp2.
Contact Process H2SO4
S → SO2 → SO3 (V2O5 catalyst, 720K, 2 atm) → H2S2O7 (oleum) → H2SO4. Exothermic, low temp favors but slow, compromise temperature.
Halogen Bond Energy
Cl-Cl (242) > Br-Br (193) > F-F (159) > I-I (151) kJ/mol. F-F weak due to small size, high lone pair repulsion, low bond dissociation.
Oxidizing Power Halogens
F2 > Cl2 > Br2 > I2. E°: F2/F- (+2.87V) > Cl2/Cl- (+1.36V) > Br2/Br- (+1.09V) > I2/I- (+0.54V). Decreases down group.
Oxoacids of Chlorine
Acidic strength: HOCl < HClO2 < HClO3 < HClO4. Increases with oxidation state (+1 to +7). Conjugate base stability increases with resonance and EN.
Interhalogen Compounds
XX' (ClF), XX'3 (ClF3 T-shaped), XX'5 (BrF5 square pyramidal), XX'7 (IF7 pentagonal bipyramidal). More reactive than halogens, strong oxidizers.
Xenon Fluorides
XeF2: linear sp3d (3 lp). XeF4: square planar sp3d2 (2 lp). XeF6: distorted octahedral sp3d3 (1 lp). All strong oxidizing and fluorinating agents.
XeO3 Structure
Pyramidal sp3, one lone pair, three Xe=O bonds. Powerful oxidizing agent, explosive. XeOF4: square pyramidal.
⚛️ d- and f-Block Elements
Electronic Config Exceptions
Cr: [Ar]3d5 4s1 (not 3d4 4s2) - half-filled stable. Cu: [Ar]3d10 4s1 (not 3d9 4s2) - fully filled stable. Similarly Mo, Ag, Au.
Lanthanoid Contraction
4f electrons poor shielding, Zeff increases across series. Size decreases La (187) to Lu (172) pm. Consequences: 4d≈5d size, basicity decreases, IE increases.
Oxidation States
Sc +3 only, Ti +2/+3/+4, V +2 to +5, Cr +2/+3/+6, Mn +2 to +7, Fe +2/+3, Co +2/+3, Ni +2, Cu +1/+2, Zn +2 only. Max = group number (up to Mn).
Color - d-d Transition
Partially filled d-orbitals: [Ti(H2O)6]3+ (d1) purple, [Cu(H2O)6]2+ (d9) blue. d-d transition absorbs visible light. Zn2+, Sc3+ colorless (d10/d0).
Color - Charge Transfer
KMnO4 purple (LMCT O→Mn), K2Cr2O7 orange (LMCT O→Cr). Intense color, no d-d transition (Mn+7 d0, Cr+6 d0). Different from d-d.
KMnO4 Preparation
2MnO2 + 4KOH + O2 → 2K2MnO4 + 2H2O (fused), then 3K2MnO4 + 2H2O → 2KMnO4 + MnO2 + 4KOH (electrolytic). Purple tetrahedral MnO4-.
KMnO4 Reactions Acidic
MnO4- + 8H+ + 5e- → Mn2+ + 4H2O (E°=+1.51V). Oxidizes Fe2+→Fe3+, C2O42-→CO2, I-→I2, H2S→S. Purple to colorless.
KMnO4 Neutral/Alkaline
Neutral: MnO4- + 2H2O + 3e- → MnO2 + 4OH- (brown ppt). Alkaline: MnO4- + e- → MnO42- (green). Different products in different medium.
K2Cr2O7 Preparation
4FeCr2O4 + 8Na2CO3 + 7O2 → 8Na2CrO4 + 2Fe2O3 + 8CO2, then acidify → Na2Cr2O7, then KCl → K2Cr2O7 (less soluble). Orange dichromate.
K2Cr2O7 Reactions
Cr2O72- + 14H+ + 6e- → 2Cr3+ + 7H2O (E°=+1.33V). Oxidizes Fe2+→Fe3+, I-→I2, H2S→S, SO2→SO42-, ethanol→acetic acid. Orange to green.
Lanthanoids Properties
Config [Xe]4f1-14 5d0-1 6s2. Common OS +3. Ce4+ (f0), Eu2+ (f7), Yb2+ (f14) stable due to empty/half/full f. All silvery white, reactive.
Magnetic Moment d-block
μ = √n(n+2) BM. Ti3+ (d1) 1.73, V3+ (d2) 2.83, Cr3+ (d3) 3.87, Mn2+ (d5 high) 5.92, Fe3+ (d5) 5.92, Co2+ (d7 high) 3.87 BM.
📋 Important Orders & Comparisons
| Property | Order | Reason |
|---|---|---|
| Acidic strength (hydrides Group 16) | H2O < H2S < H2Se < H2Te | Bond strength decreases down |
| Acidic strength (hydrides Group 17) | HF < HCl < HBr < HI | Bond strength decreases |
| Basic strength | NH3 > PH3 > AsH3 > SbH3 > BiH3 | EN decreases, lone pair availability |
| Thermal stability carbonates | BeCO3 < MgCO3 < CaCO3 < SrCO3 < BaCO3 | Lattice energy vs hydration |
| Solubility sulfates | BeSO4 > MgSO4 > CaSO4 > SrSO4 > BaSO4 | Lattice energy increases |
| Reducing power | HI > HBr > HCl > HF | Bond dissociation energy |
| Oxidizing power | F2 > Cl2 > Br2 > I2 | E° decreases down group |
| IE1 (Group 1) | Li > Na > K > Rb > Cs | Size increases, Zeff decreases |