chemistry module 3 halogens

Halogens

Group 7 non-metals, diatomic molecules at room temperature.

Boiling Point Trend

Increases down the group due to molecular size.

Diatomic Molecules

Molecules made of two identical atoms, e.g., F2.

London Forces

Weak intermolecular forces in diatomic halogen molecules.

Instantaneous Dipole

Temporary dipole caused by electron imbalances.

Induced Dipole

Dipole created in a neighboring molecule by another dipole.

Reactivity Trend

Increases up the group; chlorine most reactive.

Displacement Reaction

More reactive halogen displaces a less reactive halogen.

Chlorine Color

Very pale green solution, often colorless in water.

Bromine Color

Yellow solution in water, yellow in organic solvent.

Iodine Color

Brown solution in water, purple in organic solvent.

Halide Ions

Ions formed when halogens gain an electron.

Aqueous Solution

Water-based solution containing dissolved substances.

Organic Solvent

Non-water solvent used for halogen color tests.

Group 7

Periodic table group containing halogens.

Chlorine Reactivity

Most reactive halogen among chlorine, bromine, iodine.

Bromine Reactivity

Intermediate reactivity, less than chlorine but more than iodine.

Iodine Reactivity

Least reactive halogen in the group.

Molecular Structure

Simple molecular structures with weak intermolecular forces.

Electron Cloud

Region around an atom where electrons are likely found.

Color Observations

Visual cues indicating presence of specific halogens.

Chlorine

More reactive halogen than bromine in Group 7.

Bromide Ion

An ion formed from bromine, with a charge of -1.

Displacement Reaction

Chlorine displaces bromine from metal bromide solution.

Redox Reaction

Involves oxidation and reduction processes.

Oxidation

Loss of electrons, increasing oxidation number.

Reduction

Gain of electrons, decreasing oxidation number.

Potassium Spectator Ion

Ion that does not participate in the reaction.

Ionic Equation

Shows only the ions involved in a reaction.

Oxidising Power

Ability to gain electrons; decreases down Group 7.

Atomic Radius

Distance from nucleus to outermost electron shell.

Shielding Effect

Inner electron shells reduce nuclear attraction on outer electrons.

Halogens

Group 7 elements with 7 outer shell electrons.

Oxidising Agents

Substances that accept electrons during reactions.

Disproportionation Reaction

Same species is both oxidised and reduced.

Chloric(I) Acid

Product of chlorine and water, used for sterilisation.

Sterilising Agent

Substance that kills bacteria in water.

HClO

Chloric(I) acid, formed in chlorine-water reaction.

ClO- Ion

Hypochlorite ion, a strong sterilising agent.

Universal Indicator

pH indicator that changes color based on acidity.

Oxidation Number Change

Indicates electron transfer in redox reactions.

Sodium Hydroxide Reaction

Chlorine reacts with NaOH, showing oxidation and reduction.

Half-Equation

Shows individual oxidation or reduction processes.

Chlorine

Chemical element used for water disinfection.

HClO

Sterilising agent formed from chlorine in water.

ClO (aq)

Dissociated form of HClO in water.

Sodium chlorate (I)

Compound used as bleach and disinfectant.

Water treatment

Process of making water safe to drink.

Chlorinated hydrocarbons

Toxic byproducts from chlorine water treatment.

Halide ions

Negatively charged ions derived from halogens.

Silver nitrate

Chemical used to identify halide ions.

AgX (s)

Precipitate formed from halide ion reaction.

Silver chloride (AgCl)

White precipitate formed from chloride ions.

Silver bromide (AgBr)

Cream precipitate formed from bromide ions.

Silver iodide (AgI)

Yellow precipitate formed from iodide ions.

Ammonia

Chemical used to differentiate halide precipitates.

Dilute ammonia

Used to test solubility of silver halides.

Concentrated ammonia

Used to further test halide solubility.

Precipitate

Solid formed from a chemical reaction in solution.

False positive

Incorrect identification due to interference.

Nitric acid

Used to prevent carbonate interference in tests.

Identifying halides

Process of determining halide ions in solution.

Bacteria

Microorganisms targeted by chlorine in water treatment.

Carbonate Test

Add HCl and sodium carbonate, observe gas.

Effervescence

Bubbling gas indicating a reaction.

Carbon Dioxide (CO₂)

Gas produced in carbonate test.

Limewater

Calcium hydroxide solution used to test CO₂.

Calcium Carbonate Precipitate

White solid formed when CO₂ bubbles through limewater.

Sulfate Test

Add HCl and barium chloride to sample.

Barium Sulfate Precipitate

White solid indicates presence of sulfate ions.

Barium Nitrate

Alternative solution for sulfate testing.

Ammonium Ion Test

React with warm NaOH to produce ammonia.

Ammonia Gas

Produced from ammonium ions and NaOH.

Pungent Smell

Characteristic odor of ammonia gas.

Red Litmus Paper

Turns blue in presence of ammonia.

Dilute Hydrochloric Acid

Used to acidify samples in tests.

Sodium Carbonate Solution

Reactant in carbonate ion test.

Delivery Tube

Transfers gas from test tube to limewater.

Insoluble Calcium Carbonate

Forms when CO₂ reacts with limewater.

Positive Sulfate Result

Indicated by white barium sulfate precipitate.

Warm Aqueous Sodium Hydroxide

Used to test for ammonium ions.

Test Tube

Container for conducting chemical tests.

Clean Pipette

Used to avoid contamination in tests.