Key Points
Key Points: Electronic Configuration
| Group | Name | General Configuration | Valence e⁻ | Tendency | Key Property | Example | Special Note |
|---|---|---|---|---|---|---|---|
| 16 | Chalcogens | ns² np⁴ | 6 | Gain 2 e⁻ | Moderately reactive | O→2s²2p⁴ S→3s²3p⁴ |
Incomplete octet |
| 17 | Halogens | ns² np⁵ | 7 | Gain 1 e⁻ | Highly reactive | Cl→3s²3p⁵ Br→4s²4p⁵ | Very high electron affinity |
| 18 | Noble gases | ns² np⁶ (except He) | 8 | Stable (no gain/loss) | Inert / least reactive | Ne→2s²2p⁶ Ar→3s²3p⁶ | He = 1s² |
Key Points: Atomic and Physical Properties
Atomic Properties:
| Property | Group 16 | Group 17 | Group 18 |
|---|---|---|---|
| Atomic radius | Increases down the group, decreases across the period | Increases down the group, decreases across the period | Increases down the group, decreases across the period |
| Ionisation energy | Decreases down the group, increases across the period | High; decreases down the group | Very high |
| Electronegativity | Moderate; decreases down the group | Very high; decreases down the group | Nearly zero |
| Electron gain enthalpy | Oxygen less negative than sulphur | Fluorine less negative than chlorine | Positive values |
| General trend | Tendency to gain 2 electrons | Tendency to gain 1 electron | Stable configuration |
Physical Properties:
| Property | Group 16 | Group 17 | Group 18 |
|---|---|---|---|
| Physical state | Oxygen is gas; others are solids | Fluorine and chlorine are gases, bromine is a liquid, iodine is a solid | All are gases |
| Nature | Non-metals to metal down the group | Non-metals | Inert gases |
| Reactivity | Moderate | Very high | Very low |
| Melting and boiling point | Increase down the group | Increase down the group | Very low values |
| Special features | Show allotropy | Show characteristic colours and high reactivity | Monoatomic and chemically inert |
| Examples | O, S, Se, Te, Po | F, Cl, Br, I, At | He, Ne, Ar, Kr, Xe, Rn |
Key Points: Anomalous Behaviour of Oxygen
Reasons
- Small atomic size
- High electronegativity and ionisation energy
- Absence of d-orbitals
Important Properties
| Property | Oxygen |
|---|---|
| Nature | Diatomic gas (O₂) |
| Magnetic behaviour | Paramagnetic |
| Oxidation state | Mainly −2 |
| Hydride | H₂O is liquid at room temperature |
| Covalency | Usually 2 |
Key Points: Anomalous Behaviour of Fluorine
Reasons
- Small atomic size
- Very high electronegativity
- Absence of d-orbitals
- Low F–F bond dissociation energy
| Property | Fluorine |
|---|---|
| Oxidation state | Only −1 (does not show + states) |
| Hydride | HF is liquid (others are gases) |
| Nature | Form more ionic compounds |
| Oxyacids | Forms only one oxyacid (HOF) |
Key Points: Chemical Properties
Oxidation States:
| Group | Common Oxidation States |
|---|---|
| 16 | −2, +2, +4, +6 |
| 17 | −1, +1, +3, +5, +7 |
| 18 | 0 (Xe shows +2, +4, +6) |
Reactivity with Hydrogen:
| Property | Group 16 | Group 17 |
|---|---|---|
| Acidic strength | H₂O < H₂S < H₂Se < H₂Te | HF < HCl < HBr < HI |
| Thermal stability | H₂O > H₂S > H₂Se > H₂Te | HF > HCl > HBr > HI |
| Reducing power | H₂S < H₂Se < H₂Te | Increases down group |
Reactivity with Oxygen:
| Group | Key Points |
|---|---|
| 16 | Forms EO₂, EO₃; acidic oxides; act as oxidising & reducing agents |
| 17 | Forms oxides (Cl₂O, Cl₂O₇ etc.); strong oxidising agents |
Reactivity with Halogens:
| Group | Key Points |
|---|---|
| 16 | Forms halides (EX₂, EX₄, EX₆) |
| 17 | Forms interhalogen compounds |
| 18 | Xe, Kr form fluorides (XeF₂, XeF₄, XeF₆) |
Reactivity with Metals:
| Group | Key Points |
|---|---|
| 16 | Forms metal oxides/sulphides (MgSe, CuS) |
| 17 | Forms salts (NaCl, MgBr₂) |
| 18 | No reaction (inert) |
Allotropy:
| Element | Allotropes |
|---|---|
| Oxygen | O₂, O₃ |
| Sulfur | Rhombic, Monoclinic |
| Selenium | Red, Grey |
| Tellurium | Crystalline, Amorphous |
Key Points: Sulphur - Allotropic Forms
Allotropes of Sulphur:
| Property | Rhombic (α) | Monoclinic (β) |
|---|---|---|
| Colour | Pale yellow | Bright yellow |
| Shape | Orthorhombic | Needle-shaped |
| Melting point | 385.8 K | 393 K |
| Density | 2.06 g/cm³ | 1.98 g/cm³ |
| Stability | Stable below 369 K | Stable above 369 K |
| Solubility | Insoluble in water, soluble in CS₂ | Soluble in CS₂ |
Allotropes of Group 16:
| Element | Allotropes |
|---|---|
| Oxygen | O₂, O₃ (ozone) |
| Sulfur | Rhombic, Monoclinic |
| Selenium | Red (non-metallic), Grey (metallic) |
| Tellurium | Crystalline, Amorphous |
| Polonium | α and β (both metallic) |
Key Points: Oxoacids of Sulphur
| Name | Formula |
|---|---|
| Sulfurous acid | H₂SO₃ |
| Sulfuric acid | H₂SO₄ |
| Disulfuric (Pyrosulfuric) acid | H₂S₂O₇ |
| Peroxomonosulfuric acid | H₂SO₅ |
| Peroxodisulfuric acid | H₂S₂O₈ |
| Thiosulfuric acid | H₂S₂O₃ |
Key Points: Oxoacids of Halogens
| Oxidation state of X | Generic name | Oxoacids of fluorine | Oxoacids of chlorine | Oxoacids of bromine | Oxoacids of iodine |
|---|---|---|---|---|---|
| +1 | Hypohalous acid (HXO) | HOF | HOCl | HOBr | HOI |
| +3 | Halous acid (HXO₂) | – | HOClO | – | – |
| +5 | Halic acid (HXO₃) | – | HOClO₂ | HOBrO₂ | HOIO₂ |
| +7 | Perhalic acid (HXO₄) | – | HOClO₃ | HOBrO₃ | HOIO₃ |
Key Points: Oxygen and Compounds of Oxygen
oxygen (O₂)
Preparation:
- Heating potassium chlorate:
KClO₃ → O₂ (MnO₂ catalyst) - Electrolysis of water
Chemical Properties:
- With metals → metal oxides
2Ca + O₂ → 2CaO
4Al + 3O₂ → 2Al₂O₃ - With non-metals → non-metal oxides
C + O₂ → CO₂
P₄ + 5O₂ → P₄O₁₀ - With HCl:
4HCl + O₂ → 2H₂O + 2Cl₂ - Oxidation reaction:
2SO₂ + O₂ → 2SO₃ (V₂O₅ catalyst)
Types of Oxides:
| Type | Nature | Examples |
|---|---|---|
| Acidic | Form acids in water | SO₂, CO₂, N₂O₅ |
| Basic | Form bases in water | Na₂O, CaO, BaO |
| Amphoteric | Both acidic & basic | Al₂O₃ |
| Neutral | Neither acidic nor basic | CO, NO, N₂O |
Key Points: Compounds of Sulphur
| Property | SO₂ (Sulphur dioxide) | H₂SO₄ (Sulphuric acid) |
|---|---|---|
| Preparation | FeS₂ + O₂ → SO₂ | Contact process |
| Physical | Colourless, pungent, poisonous gas | Colourless, dense, oily liquid |
| Nature | Reducing agent | Strong acid |
| Key reactions | With O₂ → SO₃ (V₂O₅) | Dehydrating agent |
| Special reaction | Decolourises KMnO₄ | Sugar → carbon |
| Other reactions | With NaOH → Na₂SO₃ | With salts → HCl |
| Uses | Bleaching, disinfectant | Fertilisers, industry |
Key Points: Chlorine and Compounds of Chlorine
Chlorine (Cl₂):
Preparation:
- Electrolysis of NaCl
- Deacon’s process:
HCl + O₂ → Cl₂ (CuCl₂ catalyst)
Physical Properties:
- Poisonous gas
- Greenish-yellow colour
- Soluble in water → forms chlorine water
Chemical Properties:
| Type | Reaction |
|---|---|
| With metals | 2Al + 3Cl₂ → 2AlCl₃ |
| With non-metals | P₄ + 6Cl₂ → 4PCl₃ |
| With H₂ | H₂ + Cl₂ → 2HCl |
| With NH₃ | NH₃ + Cl₂ → NH₄Cl / NCl₃ |
| Oxidising property | Fe²⁺ → Fe³⁺ |
| Bleaching | Cl₂ + H₂O → HCl + HOCl → [O] (bleaching) |
Hydrogen Chloride:
Preparation:
- NaCl + H₂SO₄ → HCl
Physical Properties:
- Colourless gas
- Pungent smell
- Highly soluble in water
Chemical Properties:
- Acidic:
HCl + H₂O → H₃O⁺ + Cl⁻ - With NH₃:
NH₃ + HCl → NH₄Cl
Special (Aqua Regia)
- Au + aqua regia → AuCl₄⁻
Used for dissolving noble metals
Key Points: Interhalogen Compounds
Types of Interhalogen Compounds:
| Type | Examples |
|---|---|
| XX′ | ClF, BrF, ICl, IBr |
| XX′₃ | ClF₃, BrF₃, IF₃ |
| XX′₅ | ClF₅, BrF₅, IF₅ |
| XX′₇ | IF₇ |
Methods of Preparation:
| Method | Reactions |
|---|---|
| Direct combination | Cl₂ + F₂ → 2ClF Br₂ + 3F₂ → 2BrF₃ I₂ + 3Cl₂ → 2ICl₃ |
| Halogen + interhalogen | Br₂ + BrF₃ → 3BrF Br₂ + ClF₃ → 2BrF₃ + BrCl |
| Special (ICl) | I₂ + KClO₃ → ICl + KIO₃ |
Key Points: Compounds of Xenon
| Compound | Oxidation State of Xe | Lone Pairs on Xe | Shape |
|---|---|---|---|
| XeF₂ | +2 | 3 | Linear |
| XeF₄ | +4 | 2 | Square planar |
| XeF₆ | +6 | 1 | Distorted octahedral |
| XeO₃ | +6 | 1 | Trigonal pyramidal |
| XeOF₄ | +6 | 1 | Square pyramidal |
Concepts [14]
- Occurrence of Elements of Groups 16, 17 and 18
- Electronic Configuration of Elements of Group 16, 17 and 18
- Atomic and Physical Properties of Elements of Group 16, 17 and 18
- Anomalous Behaviour of Oxygen
- Anomalous Behaviour of Fluorine
- Chemical Properties of Elements of Groups 16, 17 and 18
- Sulphur - Allotropic Forms
- Oxoacids of Sulphur
- Oxoacids of Halogens
- Oxygen and Compounds of Oxygen
- Compounds of Sulphur
- Chlorine and Compounds of Chlorine
- Interhalogen Compounds
- Compounds of Xenon
