CIE A Level Chemistry: Physical Trends and Reactions of Group 17 Elements (Chapter 11)

Halogens

Group 17 elements used in various applications.

Water purification

Process using halogens like chlorine for cleaning.

Flame-retardants

Bromine's use in preventing fire spread.

Antiseptic agents

Iodine's role in disinfecting wounds.

Distinct colours

Halogen colours darken down the group.

Volatility

Ease of evaporation; low melting and boiling points.

Melting point

Temperature at which a solid becomes liquid.

Boiling point

Temperature at which a liquid becomes gas.

Atomic size

Increases down the Group 17 elements.

Covalent bonds

Bonds formed by overlapping atomic orbitals.

Bond strength

Attraction between bonded electrons and nuclei.

Bond enthalpy

Heat required to break one mole of bond.

Fluorine bond enthalpy

Lower than chlorine and bromine due to repulsion.

Lone pair repulsion

Repulsion between close lone pairs in fluorine.

Diatomic molecules

Molecules consisting of two identical atoms.

Simple molecular structures

Halogens form weak van der Waals' forces.

Instantaneous dipole

Temporary dipole caused by electron distribution.

Van der Waals' forces

Weak forces between diatomic halogen molecules.

Fluorine volatility

Most volatile halogen with low boiling point.

Iodine volatility

Least volatile halogen with high boiling point.

Bond strength trend

Decreases down the group due to atomic size.

Bonding pair of electrons

Electrons shared between two bonded atoms.

Induced Dipole

Temporary dipole created by electron cloud distortion.

Van der Waals' Forces

Weak intermolecular forces due to induced dipoles.

Oxidising Agent

Substance that gains electrons during a reaction.

Electronegativity

Ability of an atom to attract electrons in a bond.

Displacement Reaction

More reactive halogen replaces less reactive halogen.

Thermal Stability

Resistance of a substance to decomposition when heated.

Hydrogen Halides

Compounds formed from halogens and hydrogen gas.

Reducing Agent

Substance that donates electrons in a reaction.

Ionic Radius

Size of an atom's ion, affecting reactivity.

Silver Nitrate Test

Identifies halide ions by forming precipitates.

Precipitate

Solid formed from a solution during a chemical reaction.

Ammonia Test

Distinguishes halide ions based on precipitate solubility.

Concentrated Sulfuric Acid

Strong acid reacting with halides to produce gases.

Disproportionation Reaction

Same species is both oxidized and reduced.

Chloric Acid

Sterilizing agent formed from chlorine in water.

Bond Energy

Energy required to break a bond between atoms.

Halogen Reactivity Trend

Decreases down the group due to increased size.

Chlorine in Water

Used for purification by killing bacteria.

Hydrogen Chloride Gas

Produced from the reaction of hydrochloric acid.

Bromine Reaction with Sulfuric Acid

Produces reddish-brown bromine gas upon oxidation.

Iodine Reaction with Sulfuric Acid

Forms violet iodine vapor and sulfur upon oxidation.

Halide Ion Size

Increases down the group, affecting reactivity.

Electrons in Molecules

More electrons lead to stronger van der Waals' forces.

Halide Ion Oxidation

Halide ions lose electrons, becoming oxidized.

Hydrogen Halide Thermal Stability

Decreases down the group due to weaker bonds.

Reactivity of Halogens

Halogens become less reactive down the group.

Chlorine in Cold Alkali

Reacts to form sodium chloride and sodium hypochlorite.

Chlorine in Hot Alkali

Forms sodium chloride and sodium chlorate.

Chlorine Gas

Used in water treatment for disinfection.

Halogen Group

Group 17 elements known for reactivity.

Halogen Bond Length

Increases down the group, leading to weaker bonds.

Chlorine Displacement Reaction

Chlorine displaces bromine in a solution.

Halide Ion Identification

Precipitate color indicates specific halide ion.

Hydrogen Sulfide

Gas produced from iodide reactions, has bad smell.

Chlorine Oxidation Number

Increases during disproportionation reactions.