Groups 16, 17 & 18
Oxygen Family · Halogens · Noble Gases
Manish Dhangar · manish2stem@gmail.com
Oxygen Family
ns2 np4 — O, S, Se, Te, Po
Group 16 Overview
| Property | Oxygen | Sulphur | Se / Te |
|---|---|---|---|
| Atomic radius | Smallest | Larger | Increases down |
| Electronegativity | 3.44 (highest) | 2.58 | Decreases down |
| d-orbitals | Absent | Present | Present |
| Oxidation states | -2, -1, -1/2, +2 | -2 to +6 | -2 to +6 |
| Max covalency | 2 | 6 | 6 |
"Oxygen chota don — +2 varch thambto, +4/+6 chi power nahi"
No d-orbitals = cannot expand octet. Max OS = +2 (only OF2). Common: -2, -1 (peroxides), -1/2 (superoxides).
Hydrides — Acidity Trend
| Hydride | Bond Str. | Acidity | BP |
|---|---|---|---|
| H2O | Highest | Lowest | 100°C |
| H2S | Down | Up | -60°C |
| H2Se | Down | Up | -41°C |
| H2Te | Lowest | Highest | -2°C |
"Bond kamakam, acid tyakatyak — H2O chikta mhanun BP highest"
Weaker E-H bond = easier H+ release = stronger acid. H2O has H-bonding = anomalously high BP.
O3 vs SO2
O3 — Oxidising
Decomposes: O3 → O2 + [O]. Bleaches permanently.
SO2 — Reducing
Oxidised to SO3/H2SO4. Bleaches temporarily.
"O3 aag laavto, SO2 pani sambhalt"
Group 16 — Quick Facts
O anomaly: No d-orbitals. OS: -2, -1, -1/2, +2 only. Max covalency = 2.
Hydrides: Acidity up down group. H2O highest BP (H-bonding).
O3 = strong oxidiser. SO2 = reducing agent.
Halogens
ns2 np5 — F, Cl, Br, I
Group 17 Overview
| Element | Colour | State | Ox. Power | EGE rank |
|---|---|---|---|---|
| F2 | Pale yellow | Gas | Highest | 2nd |
| Cl2 | Greenish-yellow | Gas | 2nd | 1st (most -ve) |
| Br2 | Reddish-brown | Liquid | 3rd | 3rd |
| I2 | Violet | Solid | Lowest | Lowest |
"Pale yellow, green-yellow, red-brown, violet — rainbow order!"
Electron Gain Enthalpy
Correct Order
Cl > F > Br > I
Cl has highest EGE — NOT Fluorine!
"Fluorine cha room chota — e- la push milto, chlorine la perfect space"
F's compact 2p orbital causes interelectronic repulsion for incoming electron.
Hydrogen Halides
| Property | HF | HCl | HBr | HI |
|---|---|---|---|---|
| Bond strength | Highest | Medium | Lower | Lowest |
| Acidity | Weakest | Medium | Strong | Strongest |
| BP | Highest | Low | Medium | Higher |
"Bond strong = acid weak. HF premmadh strong, pan acid madhe weak"
Halogen Displacement
Cl2 + 2KBr → 2KCl + Br2
Orange-brown — Possible
I2 + 2KCl → No Reaction
Impossible
Group 17 — Quick Facts
Oxidising: F2 > Cl2 > Br2 > I2 (F2 strongest)
EGE: Cl > F > Br > I (Cl highest, not F!)
HX Acidity: HI > HBr > HCl > HF (HF weakest)
HF BP: Highest due to H-bonding
Displacement: Higher oxidiser displaces lower
Mnemonics (Memory Boost)
"फ्लोरिन क्लासमध्ये ब्रेक घेऊन आईकडे गेला"
(F, Cl, Br, I — group order)
"फ्लोरिन राजा पण क्लोरिन जिंकतो"
(Cl > F in EGE — always asked!)
"बंध कमकुवत = आम्ल ताकदवान"
(Strong H-F bond = weak acid)
"फक्त odd पार्टी — 1, 3, 5, 7"
(Interhalogens: only AX, AX3, AX5, AX7 exist)
Noble Gases + Interhalogens
ns2 np6 (He = 1s2)
Group 18 — Key Concepts
| Gas | No. | Key Fact | Use |
|---|---|---|---|
| He | 2 | Sun spectrum | Balloons, cryogenics |
| Ne | 10 | Discharge glow | Neon signs |
| Ar | 18 | 0.93% in air | Welding |
| Xe | 54 | Stable compounds | Xe lamps |
| Rn | 86 | Radioactive | Cancer treatment |
Xenon Shapes
| Compound | Hybrid. | LP | Shape |
|---|---|---|---|
| XeF2 | sp3d | 3 | Linear |
| XeF4 | sp3d2 | 2 | Square Planar |
| XeF6 | sp3d3 | 1 | Distorted Octahedral |
| XeO3 | sp3 | 1 | Pyramidal |
| XeOF4 | sp3d2 | 1 | Square Pyramidal |
| XeO4 | sp3 | 0 | Tetrahedral |
"2 सरळ, 4 चौकोन, 6 गोंधळ — lone pairs hi reason"
Xe OS: +2 (XeF2), +4 (XeF4), +6 (XeF6, XeO3), +8 (XeO4 rare). More LP = more distortion.
Interhalogens
| Type | Examples | Shape |
|---|---|---|
| AX | ClF, BrCl | Linear |
| AX3 | ClF3, BrF3 | T-shaped |
| AX5 | BrF5, IF5 | Square Pyramidal |
| AX7 | IF7 | Pentagonal Bipyramidal |
Mnemonics (Memory Boost)
"हेलियम ने आकाशात क्रांती करून एक्स-रे गेला"
(He, Ne, Ar, Kr, Xe, Rn — group order)
"झेनॉन बोर झाला — शेवटी रिअॅक्ट झाला"
(Xe gets bored, reacts with F and O)
"2 सरळ, 4 चौकोन, 6 गोंधळ"
(XeF2 linear, XeF4 sq.planar, XeF6 distorted oct)
Final Exam Traps
From real PYQs
Wrong
Oxygen shows +6 OS
Correct
O max OS = +2 only in OF2
Wrong
F has highest EGE
Correct
Cl > F > Br > I
Wrong
Oxidising: Cl > F
Correct
F2 > Cl2 > Br2 > I2
Wrong
Bond up = acid up
Correct
Weaker bond = stronger acid
Wrong
Noble gases never react
Correct
Xe forms stable compounds
Universal Mnemonic
"मोठं झालं की कंट्रोल की कमी"
(Bigger atomic size = weaker bond = stronger acid — applies to both Gr 16 & 17 hydrides)
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