P-Block Elements (Part 2)

Introduction

• Second marathon session of P-block elements. Focus: Group 15 and Group 16
• Gave a self-introduction at the beginning of the session.
• Important to pay attention because it includes previous years' questions (PYQs) and potential questions.
• Planned to cover Groups 15, 16, 17, 18 completely, but took more time to prepare the file, so Group 17 and 18 will be done in a separate marathon.

Group 15 (Nitrogen Family)

Members

• Nitrogen (N)
• Phosphorus (P)
• Arsenic (As)
• Antimony (Sb)
• Bismuth (Bi)
• Mnemonic: New Zealand for India - N P As Sb Bi
• Nitrogen, Phosphorous: Non-metals
• Arsenic, Antimony: Metalloids
• Bismuth: Metal

General Electronic Configuration

• ns2 np3
• Generalized: [inert gas] (n-2)f14 (n-1)d10 ns2 np3

Variation/Trends

• Size (Top-to-Bottom): Increases
• Ionization Energy: Nitrogen > Phosphorus > Arsenic > Antimony > Bismuth
• Electron Affinity: Nitrogen is the lowest (half-filled configuration)
• Electronegativity: Nitrogen > Phosphorus > Arsenic > Antimony > Bismuth
• Melting Point (MP): Arsenic > Antimony > Bismuth > Phosphorus > Nitrogen
• Metallic Character: Nitrogen < Phosphorus < Arsenic < Antimony < Bismuth

Oxidation States

• Major: -3, +3, +5
• Nitrogen oxidation states variation: +1 (N2O), +2 (NO)
• Inert Pair Effect: Down the group +5 stability decreases, +3 stability increases

Specific Properties (Anomalous Behavior of Nitrogen)

• Small size, high electronegativity
• Multiple bonds (double, triple)
• Absence of vacant d-orbitals
• Nitrogen exists in the form of a triple bond N≡N

Reactivity

With Hydrogen

• Hydrides with E-2 (EX3): NH3 (isothermic), PH3 (endothermic)
• Bond energy: NH3 > PH3 > AsH3 > SbH3 > BiH3
• Lewis base nature: NH3 > PH3 > stops
• Reducing nature: BiH3 > SbH3 > AsH3 > PH3 > NH3

With Oxygen

• Usual distribution: E2O3 and E2O5
• Combination: E2O5 acidic, E2O3 in non-metals-slightly acidic, in metalloids-amphoteric, in metals-basic

Preparation and Properties of Nitrogen

• Preparation: Heating Ammonium Dichromate, Heating Ammonium Nitrite, Heating Sodium Azide/ Barium Azide, Heating PbNO3
• Properties: Colorless, Odorless, Non-toxic, Inert atmosphere provider

Compounds of Nitrogen

• Ammonia (NH3): NH4Cl + Base → NH3 + Salt
• Ammonium Phosphate: N2 + H2 → NH3 (Haber's process)
• Electron Affinity: Low; high affinity does not attract chunks luring

With Halogens

• HCl + E forms EClx; only NF3 is quite stable for nitrogen, NCl3 and mixtures are unstable

Group 16 (Oxygen Family)

Members

• Oxygen (O)
• Sulfur (S)
• Selenium (Se)
• Tellurium (Te)
• Polonium (Po)
• Mnemonic: O Se Te Po

General Electronic Configuration

• General: ns2 np4

Variation/Trends

• Size: Increases (Top-to-Bottom)
• Ionization Energy: Decreases down the group
• Electron Affinity: Oxygen low because of repulsions
• Electronegativity: O > S > Se > Te > Po
• Melting Point: Oxygen < Sulfur < Selenium < Tellurium < Polonium

Oxidation States

• Mainly -2, +2, +4, +6
• Oxygen: Limited oxidation states (zero to +2) shown only with fluorine.
• Sulfur and others: Mainly +4 and +6

Specific Properties (Anomalous Behavior of Oxygen)

• Small size, high electronegativity
• Absence of d-orbitals
• Oxygen as O2, sulfur as S8

Reactivity

With Hydrogen

• Halides EH2; H2O-H2S-Strength H2S-Decreases Down The Group
• Bond angle largely around 90°
• Bond strength: H2O > H2S > H2Se > H2Te
• Acidic nature: H2S (more) > H2Se > H2Te (increases)
• Thermal stability: H2Se > H2Te > H2S > H2O (requires high temperature)

With Oxygen

e.g., EO2, EO3

• Reducing property: SO2 > SeO2 > TeO2 (more)
• Acidity: EO2 and EO3 (acidic)

With Halogens

e.g., EX2, EX4, EX6

• Fluoride reactivity: SF6 (least) > SeF6 > TeF6
• Rate of hydrolysis: SF6 least
• Monohalides exist in dimeric forms, like Se2Cl2 (unstable)

Oxygen and Ozone

Preparation

Preparation of Pure Oxygen

• Heating KClO3: KCl + O2
• Heating KMnO4: MnO2 + K2MnO4 + O2
• Heating K2Cr2O7: Cr2O3 + O2 + K2CrO4
• Decomposition of H2O2: H2O + O2
• Industrial Method: Fractional Distillation of Liquid Air

Properties

• Colorless, Odorless, Non-toxic, Slightly Water Soluble
• High boiling point for water (373 K)
• Paramagnetic nature

Ozone

• Allotrope of Oxygen
• Preparation: Silent electric discharge through O2
• Properties: Colorless (low conc.), Pale-Blue, Highly Toxic at High Concentration, Good Oxidizing Agent
• Uses: K2MnO4, K2Cr2O7, Cl2

Sulfur and its Compounds

Allotrope

Allotropes of Sulfur (Important Points)

• Rhombic (S8): Stable below 369K
• Monoclinic (S8): Stable above 369K
• Density: Rhombic > Monoclinic
• Melting Point: Monoclinic > Rhombic
• S6 is also important (Chair down-triangle Configuration)

Hydrogen Sulfide (H2S)

• Properties: Colorless, Rotten Egg Smell, Diamagnetic, Reducing Gas
• Reducing: SO2
• Detection: PbAc2 → Black PPT

Sulfur Dioxide (SO2)

Preparation

• Properties: Colorless, Pungent Odor, Suffocating
• Industrial: Burning S or Metal Sulfide Ores
• Properties:
• Acidity: H2O + SO2 → H2SO3 (Sulfurous Acid)
• Redox: SO2 → H2O → H2SO3 with lime water

Sulfuric Acid (H2SO4)

• Contact process: SO2 + H2SO4 → {OH} with Critical → H2SO4
• Dilute / Concentrated: choose which one to use
• Properties: Dehydrator, Remove humidity