Group 17 Elements - The Halogens

Real-Life Connection: From Salt to Sanitizers

The salt you sprinkle on food contains chlorine! Swimming pools smell of chlorine (actually HOCl). Iodine tincture treats wounds, while fluoride in toothpaste prevents cavities. Bleaching powder whitens clothes, and brominated flame retardants prevent fires. The halogens - from the Greek “halo-genes” (salt-formers) - are essential in daily life, from water purification to PVC pipes!

Group 17 Elements Overview

Members: Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At)

Common Name: Halogens (salt-formers)

Electronic Configuration Pattern

• General configuration: ns² np⁵
• Fluorine: [He] 2s² 2p⁵
• Chlorine: [Ne] 3s² 3p⁵
• Bromine: [Ar] 3d¹⁰ 4s² 4p⁵

Memory Trick - “FBI Catches Idiots Always Thoroughly”: F, Br, I, Cl, At (rearrange to F, Cl, Br, I, At)

Key Trends Down the Group

Memory Trick for Trends: “FIRE Destroys” - F is most reactive, I is least; Reactivity Electronegativity Decreases

Interactive Demo: Visualize Group 17 in the Periodic Table

Explore the halogen family and their position in the periodic table.

Exception Alert:

1. Electron gain enthalpy of Cl > F (F is small, more electron-electron repulsion)
2. Bond energy: F-F < Cl-Cl (F is small, lone pair repulsion)

Physical Properties

Memory Trick: “Ghastly Green Liquid Red Solid Violet” - Gas (green), Liquid (red), Solid (violet)

General Properties of Halogens

Oxidation States

Common: -1 (most stable, gaining 1 electron) Others: +1, +3, +5, +7 (except F, only -1)

Why doesn’t F show positive oxidation states?

• Most electronegative (no element can pull electrons from F)
• No d-orbitals for expansion
• Small size, high ionization energy

Examples:

• Cl: -1 (HCl), +1 (HOCl), +3 (HClO₂), +5 (HClO₃), +7 (HClO₄)
• Br: -1 (HBr), +1, +3, +5
• I: -1 (HI), +1, +3, +5, +7

Memory Trick: “Fluorine = Fixed at -1, Others = Odd numbers +1,+3,+5,+7”

Oxidizing Power

Order: F₂ > Cl₂ > Br₂ > I₂

Why?

• Related to electron gain enthalpy, bond dissociation energy, hydration energy
• F₂ is strongest oxidizer despite low electron gain enthalpy
• High hydration energy of F⁻ compensates

Displacement Reactions:

Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂ (Cl₂ oxidizes Br⁻)
Cl₂ + 2I⁻ → 2Cl⁻ + I₂ (Cl₂ oxidizes I⁻)
Br₂ + 2I⁻ → 2Br⁻ + I₂ (Br₂ oxidizes I⁻)

Memory Rule: More reactive halogen displaces less reactive halogen from its salt

Fluorine - The Most Reactive Element

Preparation

Cannot be prepared by chemical oxidation (no oxidizing agent strong enough!)

Electrolysis (only method):

2KHF₂ --electrolysis--> 2KF + H₂ + F₂
(Moissan's method, in Ni or Monel metal container)

Properties of Fluorine

Physical:

• Pale yellow gas
• Pungent smell
• Extremely corrosive

Chemical (most reactive element):

1. With metals (vigorous, even cold):

2Fe + 3F₂ → 2FeF₃

2. With non-metals:

H₂ + F₂ → 2HF (explosive, even in dark and cold!)
S + 3F₂ → SF₆
Xe + F₂ → XeF₂, XeF₄, XeF₆

3. With water:

2F₂ + 2H₂O → 4HF + O₂

4. With glass (SiO₂):

SiO₂ + 4HF → SiF₄ + 2H₂O
(Cannot store HF in glass bottles!)

Hydrogen Fluoride (HF)

Preparation:

CaF₂ + H₂SO₄ → CaSO₄ + 2HF (cannot use glass apparatus)

Structure:

• Strongest hydrogen bonding among HX
• Exists as (HF)ₙ chains/rings
• H-F bond is most polar

Properties:

• Weak acid in dilute solution (due to H-bonding, difficult ionization)
• Attacks glass (etching glass)
• Boiling point: 293 K (highest among HX due to H-bonding)

Paradox: HF is weakest acid among HX despite F being most electronegative! Reason: Extensive H-bonding makes ionization difficult

Reactions:

HF + NaOH → NaF + H₂O
4HF + SiO₂ → SiF₄ + 2H₂O
2HF + H₂SiF₆ → 2H₃O⁺ + SiF₆²⁻ (behaves like strong acid with H₂SiF₆)

Uses:

• Glass etching
• Fluorine production
• Fluorocarbons synthesis

Chlorine - The Greenish-Yellow Gas

Preparation

Laboratory (Deacon’s process):

4HCl + O₂ --CuCl₂, 723K--> 2Cl₂ + 2H₂O

Laboratory (Oxidation of HCl):

4HCl + MnO₂ --heat--> MnCl₂ + 2H₂O + Cl₂
16HCl + 2KMnO₄ → 2KCl + 2MnCl₂ + 8H₂O + 5Cl₂
2KMnO₄ + 16HCl(conc) → 2KCl + 2MnCl₂ + 8H₂O + 5Cl₂
4HCl(conc) + K₂Cr₂O₇ → 2KCl + 2CrCl₃ + 4H₂O + 3Cl₂

Industrial (Electrolysis of brine):

2NaCl + 2H₂O --electrolysis--> 2NaOH + Cl₂ + H₂
(Chlor-alkali process)

Cathode: 2H₂O + 2e⁻ → H₂ + 2OH⁻
Anode: 2Cl⁻ → Cl₂ + 2e⁻

Memory Trick: “MnO₂, KMnO₄, K₂Cr₂O₇ + HCl → Cl₂” (all oxidizing agents)

Properties of Chlorine

Physical:

• Greenish-yellow gas
• Pungent, suffocating smell
• Poisonous (used as war gas in WWI)
• 2.5 times heavier than air

Chemical:

1. With metals:

2Na + Cl₂ → 2NaCl (burns with golden yellow flame)
2Fe + 3Cl₂ → 2FeCl₃ (anhydrous FeCl₃)
Cu + Cl₂ → CuCl₂

2. With non-metals:

H₂ + Cl₂ → 2HCl (explosive in sunlight)
2P + 3Cl₂ → 2PCl₃ (excess P)
2P + 5Cl₂ → 2PCl₅ (excess Cl₂)

3. With water (disproportionation):

Cl₂ + H₂O ⇌ HCl + HOCl (hypochlorous acid)
HOCl ⇌ H⁺ + OCl⁻

In sunlight:

2Cl₂ + 2H₂O --sunlight--> 4HCl + O₂

4. With alkalis:

Cold dilute:

Cl₂ + 2NaOH → NaCl + NaOCl + H₂O (sodium hypochlorite)
                      (bleaching solution)

Hot concentrated:

3Cl₂ + 6NaOH → 5NaCl + NaClO₃ + 3H₂O (sodium chlorate)

Memory Trick: “Cold = Chlorite sounds cool (+1), Hot = Chlorate (+5)”

5. With hydrocarbons:

Substitution (in sunlight/UV):

CH₄ + Cl₂ --UV--> CH₃Cl + HCl

Addition (in dark):

C₂H₄ + Cl₂ → C₂H₄Cl₂ (1,2-dichloroethane)

6. Oxidizing properties:

Cl₂ + H₂S → 2HCl + S (turbidity)
Cl₂ + 2FeSO₄ → 2FeCl₂ + Fe₂(SO₄)₃
Cl₂ + 2I⁻ → 2Cl⁻ + I₂
Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂

7. Bleaching action:

Cl₂ + H₂O → HCl + HOCl
HOCl → HCl + [O] (nascent oxygen)
Coloring matter + [O] → Colorless (oxidized)

Permanent bleaching (oxidation, not reversible)

Uses:

• Water purification
• Bleaching agent (paper, textiles)
• Manufacturing of HCl, bleaching powder
• Disinfectant
• PVC, pesticides, solvents

Hydrogen Chloride (HCl)

Preparation

Laboratory:

NaCl + H₂SO₄(conc) --<200°C--> NaHSO₄ + HCl
(Cannot use glass-stoppered bottles, use rubber cork)

Alternative:
H₂ + Cl₂ --sunlight--> 2HCl (explosive)

Industrial:

H₂ + Cl₂ → 2HCl (direct combination)

Properties:

• Colorless gas, pungent smell
• Extremely soluble in water (1:450 volumes)
• Forms white fumes with NH₃ (test for HCl/NH₃)
• Concentrated HCl (37% solution) fumes in moist air

Reactions:

1. Acidic nature:

HCl + NaOH → NaCl + H₂O
2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂

2. With metals:

Zn + 2HCl → ZnCl₂ + H₂
Fe + 2HCl → FeCl₂ + H₂ (not FeCl₃)

3. With ammonia (white fumes test):

HCl + NH₃ → NH₄Cl (white fumes)

4. Reducing agent (conc. HCl):

4HCl + MnO₂ → MnCl₂ + 2H₂O + Cl₂
4HCl + PbO₂ → PbCl₂ + 2H₂O + Cl₂
2HCl + H₂O₂ → 2H₂O + Cl₂

Aqua Regia (3 HCl : 1 HNO₃):

Au + 4HCl + HNO₃ → HAuCl₄ + NO + 2H₂O

Bleaching Powder (Chlorine-based Bleach)

Formula: CaOCl₂ or Ca(OCl)Cl (calcium oxychloride) Common name: Chlorinated lime

Preparation:

Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
(Dry slaked lime + Cl₂ gas)

Structure:

• One Cl attached as Cl⁻
• One Cl attached as OCl⁻
• Mixed salt: CaCl₂·Ca(OCl)₂ (more accurate)

Properties:

• White powder, smell of chlorine
• Soluble in water (turbid solution)
• Contains ~35-38% available chlorine

Reactions:

1. With dilute acids (releases Cl₂):

CaOCl₂ + H₂SO₄(dil) → CaSO₄ + H₂O + Cl₂
CaOCl₂ + 2HCl → CaCl₂ + H₂O + Cl₂

2. With excess dilute acids:

CaOCl₂ + 2HCl(excess) → CaCl₂ + H₂O + Cl₂

3. With CO₂ (bleaching action):

CaOCl₂ + CO₂ → CaCO₃ + Cl₂
(This Cl₂ bleaches in presence of moisture)

4. Oxidizing agent:

CaOCl₂ + 2HCl → CaCl₂ + H₂O + Cl₂

Uses:

• Bleaching cotton, linen, wood pulp
• Disinfectant for drinking water
• Oxidizing agent in chemical industry
• Chloroform manufacture

Memory Trick: “BODA = Bleaching powder from Oxide (lime) + Dry Air (Cl₂)”

Bromine and Iodine

Bromine (Br₂)

Occurrence: Sea water (as bromides), salt deposits

Extraction:

2Br⁻ + Cl₂ → Br₂ + 2Cl⁻ (displacement by Cl₂)

Properties:

• Only liquid non-metal
• Reddish-brown, volatile
• Poisonous vapors
• Moderately soluble in water

Uses: Flame retardants, fumigants, dyes, pharmaceuticals

Iodine (I₂)

Occurrence: Seaweeds (kelp), Chilean saltpeter (NaIO₃)

Extraction:

From seaweed ash:
2I⁻ + Cl₂ → I₂ + 2Cl⁻

From NaIO₃:
2NaIO₃ + 5NaHSO₃ → 3NaHSO₄ + 2Na₂SO₄ + H₂O + I₂

Properties:

• Violet-black solid, lustrous
• Sublimes to violet vapor
• Sparingly soluble in water
• Soluble in KI solution: I₂ + I⁻ → I₃⁻ (brown solution)
• Soluble in organic solvents (CCl₄ - violet, CHCl₃ - brown)

Test for starch:

Starch + I₂ → Blue-black complex

Reactions:

1. With metals:

2Al + 3I₂ → 2AlI₃

2. With alkalis:

I₂ + 2NaOH → NaI + NaOI + H₂O (cold)
3I₂ + 6NaOH → 5NaI + NaIO₃ + 3H₂O (hot)

3. Oxidizing agent (mild):

I₂ + H₂S → 2HI + S
I₂ + 2Na₂S₂O₃ → 2NaI + Na₂S₄O₆ (iodometry - volumetric analysis)

Uses: Tincture iodine (antiseptic), iodized salt, pharmaceuticals, photography

Hydrogen Halides (HX)

Comparison of HF, HCl, HBr, HI

Trends:

1. Boiling point: HF »> HCl < HBr < HI

   • HF anomalous due to H-bonding
   • HCl to HI: van der Waals forces increase

2. Acidic strength: HF < HCl < HBr < HI

   • Bond strength decreases
   • Larger atom, easier H⁺ release

3. Reducing power: HF < HCl < HBr < HI

   • Easier to lose H (oxidize to X₂)

Memory Trick: “FBI Hierarchy = F weakest acid, I strongest; Bond Increases, Acid Increases”

Preparation of Hydrogen Halides

General method (not for HBr, HI):

NaX + H₂SO₄(conc) → NaHSO₄ + HX (X = F, Cl)

For HBr, HI (cannot use H₂SO₄):

NaBr + H₃PO₄ → NaH₂PO₄ + HBr
NaI + H₃PO₄ → NaH₂PO₄ + HI

Why not H₂SO₄?
2HBr + H₂SO₄ → Br₂ + SO₂ + 2H₂O (oxidizes to Br₂)
2HI + H₂SO₄ → I₂ + SO₂ + 2H₂O (oxidizes to I₂)

Memory Trick: “FBI (F,Br,I) = F uses H₂SO₄, Br & I use H₃PO₄”

Interhalogen Compounds

Definition: Compounds formed between two different halogens

General formulas: XX’, XX’₃, XX’₅, XX’₇

• X = larger, less electronegative halogen (central atom)
• X’ = smaller, more electronegative halogen

Examples:

Important Properties:

1. More reactive than parent halogens (except F₂)
2. Covalent compounds
3. Undergo hydrolysis
4. Act as strong oxidizing agents

Examples in detail:

1. Chlorine Trifluoride (ClF₃)

Preparation:

Cl₂ + 3F₂ → 2ClF₃ (at 500 K, Cu vessel)

Structure:

• T-shaped (sp³d hybridization)
• Two lone pairs on equatorial positions

Properties:

• Colorless gas
• Very reactive
• Strong fluorinating agent

Reactions:

ClF₃ + H₂O → HF + HClO₂

2. Iodine Pentafluoride (IF₅)

Preparation:

I₂ + 5F₂ → 2IF₅ (at 543 K)

Structure:

• Square pyramidal (sp³d² hybridization)
• One lone pair

Reactions:

IF₅ + H₂O → HIO₃ + HF

3. Iodine Heptafluoride (IF₇)

Preparation:

I₂ + 7F₂ → 2IF₇ (at 533 K under pressure)

Structure:

• Pentagonal bipyramidal (sp³d³ hybridization)
• No lone pairs
• Perfect symmetry

Properties:

• Colorless gas
• Most stable interhalogen

4. Iodine Monochloride (ICl)

Preparation:

I₂ + Cl₂ → 2ICl

Properties:

• Reddish-brown liquid
• Disproportionates: 3ICl ⇌ ICl₃ + I₂

Why are interhalogens more reactive?

• X-X’ bond weaker than X-X bond
• More polar (different electronegativities)
• Easier to break and react

Memory Trick: “INTER = INcreased TEnsion, More Reactive”

Oxoacids of Halogens

General trend: Acidic strength increases with oxidation state

Chlorine Oxoacids

Trend: HOCl < HClO₂ < HClO₃ < HClO₄ (acidity and stability)

Why does acidity increase?

• More O atoms withdraw electron density from O-H bond
• Easier to release H⁺
• Conjugate base more stable (resonance)

Hypochlorous Acid (HOCl)

Preparation:

Cl₂ + H₂O ⇌ HCl + HOCl

Properties:

• Weak acid
• Unstable (exists only in solution)
• Good oxidizing agent
• Bleaching agent

Disproportionation:

3HOCl → HClO₃ + 2HCl

Chloric Acid (HClO₃)

Preparation:

3Cl₂ + 6NaOH(hot) → 5NaCl + NaClO₃ + 3H₂O
NaClO₃ + H₂SO₄ → NaHSO₄ + HClO₃

Properties:

• Strong acid
• Strong oxidizing agent
• Unstable, decomposes on heating

Perchloric Acid (HClO₄)

Preparation:

NaClO₄ + H₂SO₄ → NaHSO₄ + HClO₄

Properties:

• Strongest acid (stronger than H₂SO₄)
• Hygroscopic
• Powerful oxidizing agent (hot, concentrated)
• Relatively stable (can be distilled)

Why is HClO₄ stronger than HClO?

• 4 O atoms in ClO₄⁻ stabilize negative charge (resonance)
• 1 O atom in ClO⁻ less stabilization
• More stable conjugate base = stronger acid

Memory Trick: “More O = More Oxy = More Acidic”

Common Mistakes to Avoid

1. Mistake: F shows positive oxidation states

   • Correct: F only shows -1 (most electronegative)

2. Mistake: F-F bond is strongest among halogens

   • Correct: Cl-Cl > Br-Br > F-F > I-I (F-F weak due to repulsion)

3. Mistake: HF is strongest acid among HX

   • Correct: HI > HBr > HCl > HF (HF weakest due to H-bonding)

4. Mistake: Can prepare HBr/HI using conc. H₂SO₄

   • Correct: H₂SO₄ oxidizes to Br₂/I₂, use H₃PO₄

5. Mistake: Bleaching powder formula is CaCl₂

   • Correct: CaOCl₂ or Ca(OCl)Cl

6. Mistake: Chlorine bleaches by reduction

   • Correct: Chlorine bleaches by oxidation (HOCl → [O])

7. Mistake: In XX’ₙ, X is more electronegative

   • Correct: X’ is more electronegative, X is central atom

8. Mistake: HOCl is stronger acid than HClO₄

   • Correct: HClO₄ > HClO₃ > HClO₂ > HOCl

Practice Problems

Level 1: JEE Main Basics

1. Why is F₂ most reactive among halogens despite having low electron gain enthalpy?

2. Arrange in order of: a) Acidic strength: HF, HCl, HBr, HI b) Bond strength: F₂, Cl₂, Br₂, I₂ c) Oxidizing power: F₂, Cl₂, Br₂, I₂

3. Write balanced equations for: a) Laboratory preparation of Cl₂ from MnO₂ b) Bleaching powder from slaked lime c) Aqua regia action on gold

4. Why can’t we use conc. H₂SO₄ to prepare HI from NaI?

5. What is the oxidation state of Cl in: HOCl, HClO₂, HClO₃, HClO₄?

Level 2: JEE Main Advanced

6. Explain why: a) HF is stored in wax/plastic bottles, not glass b) Bleaching by Cl₂ is permanent but by SO₂ is temporary c) Electron gain enthalpy of Cl is more negative than F

7. Complete and balance: a) Cl₂ + NaOH (cold, dil) → b) Cl₂ + NaOH (hot, conc) → c) I₂ + Na₂S₂O₃ →

8. Draw the structure of: a) ClF₃ b) IF₅ c) IF₇

9. In the chlor-alkali process, why is diaphragm used to separate anode and cathode compartments?

10. Arrange the following in order of increasing acidic strength: HOCl, HClO₂, HClO₃, HClO₄. Explain.

Level 3: JEE Advanced

11. Although F is most electronegative, HF is weakest acid among hydrogen halides. Explain this apparent contradiction.

12. The boiling points of HX follow the order: HF (293 K) » HCl (189 K) < HBr (206 K) < HI (238 K). Explain the trend and the anomaly.

13. When Cl₂ reacts with water, it undergoes disproportionation. Write the equation and calculate the oxidation states to verify disproportionation.

14. IF₇ exists but FCl₇ does not. Explain based on: a) Size of central atom b) Availability of d-orbitals

15. Calculate the bond order of: a) Cl₂ b) ClO⁻ c) ClO₂⁻ d) ClO₃⁻ e) ClO₄⁻ Comment on the trend in Cl-O bond length.

Cross-Links to Other Topics

Related to Periodic Classification

• Periodic Trends - Electron gain enthalpy anomaly
• Electronegativity - F highest value

Related to Chemical Bonding

• Hydrogen Bonding - HF anomalous b.p.
• Hybridization - Interhalogen structures
• VSEPR Theory - ClF₃, IF₅, IF₇ shapes

Related to Acids and Bases

• Acid Strength - HX trend, oxoacids

Related to Other Chapters

• Redox Reactions - Displacement reactions
• Electrochemistry - Chlor-alkali process
• Qualitative Analysis - Halide tests

Memory Palace for Group 17

Imagine a Halogen Factory:

Entrance: Sign “FBI Catches Idiots” (F, Br, I, Cl rearranged)

Color Room:

• F₂ cylinder (pale yellow gas)
• Cl₂ cylinder (greenish-yellow gas)
• Br₂ bottle (reddish-brown liquid)
• I₂ crystals (violet-black solid, purple vapor)

Reactivity Tower (7 floors):

• Floor 7 (Top): F₂ - most reactive, attacks everything
• Floor 6: Cl₂ - very reactive
• Floor 5: Br₂ - moderate
• Floor 4: I₂ - least reactive
• Elevator: Reactivity decreases going down

HX Corridor:

• HF room: Plastic bottles only, H-bonding chains visible
• HCl room: Glass bottles, strong acid labels
• HBr room: Reducing agent warnings
• HI room: Strongest acid, strongest reducing agent signs
• Acidity increases sign: HF → HI

Bleaching Department:

• Cl₂ tank with “Permanent” label
• Bleaching powder bags (CaOCl₂)
• Ca(OH)₂ + Cl₂ mixing chamber
• White fabrics hanging

Interhalogen Laboratory:

• ClF₃ model: T-shaped
• IF₅ model: Square pyramidal
• IF₇ model: Pentagonal bipyramidal
• “More Reactive Than Parents” warning sign

Oxoacid Gallery (4 paintings):

• HOCl portrait: +1, weak, unstable
• HClO₂ portrait: +3, weak
• HClO₃ portrait: +5, strong
• HClO₄ portrait: +7, strongest, most stable
• Frame size increases (acidity trend)

Quick Revision Checklist

• Group 17 configuration: ns² np⁵
• Reactivity: F₂ > Cl₂ > Br₂ > I₂
• F only -1 oxidation state
• Bond energy: Cl-Cl > Br-Br > F-F > I-I
• Electron gain: Cl > F (exception)
• F₂ prepared by electrolysis only
• HF weakest acid (H-bonding), stored in plastic
• Acidity: HI > HBr > HCl > HF
• Cl₂ lab: MnO₂ + HCl or electrolysis of brine
• Cl₂ + H₂O → HCl + HOCl (disproportionation)
• Bleaching powder: CaOCl₂, from Ca(OH)₂ + Cl₂
• Can’t prepare HBr/HI with H₂SO₄ (use H₃PO₄)
• Interhalogens: XX’ₙ (n = 1,3,5,7), more reactive
• Oxoacid acidity: HClO₄ > HClO₃ > HClO₂ > HOCl
• Aqua regia: 3 HCl : 1 HNO₃

Important Equations Summary

1. Cl₂ lab: 4HCl + MnO₂ → MnCl₂ + 2H₂O + Cl₂
2. Cl₂ industrial: 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
3. HCl lab: NaCl + H₂SO₄ → NaHSO₄ + HCl
4. HBr/HI: NaBr + H₃PO₄ → NaH₂PO₄ + HBr
5. Bleaching powder: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
6. Cl₂ + water: Cl₂ + H₂O ⇌ HCl + HOCl
7. Cl₂ + cold NaOH: Cl₂ + 2NaOH → NaCl + NaOCl + H₂O
8. Cl₂ + hot NaOH: 3Cl₂ + 6NaOH → 5NaCl + NaClO₃ + 3H₂O
9. Displacement: Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂
10. Iodometry: I₂ + 2Na₂S₂O₃ → 2NaI + Na₂S₄O₆
11. Aqua regia: Au + 4HCl + HNO₃ → HAuCl₄ + NO + 2H₂O
12. ClF₃: Cl₂ + 3F₂ → 2ClF₃
13. IF₅: I₂ + 5F₂ → 2IF₅
14. IF₇: I₂ + 7F₂ → 2IF₇
15. I₂ test: Starch + I₂ → Blue-black complex

Last updated: July 2025 Previous: Group 16 Elements | Next: Group 18 Elements