Group 7 elements

• MOST REACTIVE non-metallic group • In nature they exist in the form of their stable halide ions either dissolved in the sea or combined with K+ or Na+ forming solid deposits. • At RTP, they exist as DIATOMIC molecules • Have 7 electrons in their outer shell • Electron configuration ends in ns2 np5 where n is the highest shell number or energy level.

INCREASES down the group: • The STRENGTH of the LONDON FORCES INCREASES. • This is due to the INCREASE in the number of ELECTRONS in the diatomic molecules going down the group. • This leads to LARGER TEMPORARY DIPOLES. • MORE ENERGY is required to separate the molecules.

The PHYSICAL STATES of the elements changes from a GAS to SOLID down the group. Fluorine ~ pale yellow GAS Chlorine ~ pale green GAS Bromine ~ red-brown LIQUID Iodine ~ shiny grey-black SOLID Astatine ~ never been seen (radioactive)

DECREASES down the group. This is because the following INCREASE: - Radius of the atom - Distance between bonding electrons and nucleus - Number of electron shells - Nuclear charge Therefore: The ATTRACTION of the nucleus for the bonding pair of electrons DECREASES and therefore also the electronegativity.

OXIDISING AGENTS: - halogens have seven electrons in the outer shell so want to gain one electron. - This gain in electrons is called REDUCTION so they are behaving as oxidising agents. OXIDISING STRENGTH: - The ability of a halogen to attract an electron to form a halide ion. - DECREASES down the group due to same reasoning as trend in electronegativity.

• A MORE REACTIVE halogen will oxidise and displace the halide ion of a less reactive halogen. Chlorine ~ bromide or iodide Bromine ~ iodide

Chlorine: water ~ pale green cyclohexane ~ pale green Bromine: water ~ orange cyclohexane ~ orange Iodine : water ~ brown cyclohexane ~ violet/purple *cyclohexane (organic solvent containing C&H)

Chlorine + sodium bromide ——– sodium chloride + bromine Observation before ~ PALE GREEN: BROMINE is less reactive than CHLORINE Observation after ~ ORANGE colour in cyclohexane layer : Dure to NON-POLAR bromine being more soluble in cyclohexane. • Chlorine OXIDSES and DISPLACES bromide ions. • The redox reaction shows chorine is more reactive than bromine.

A type of REDOX reaction in which an elements is BOTH oxidised and reduced.

WATER PURIFICATION ~ adding chlorine to water to kill bacteria and make it safe to drink. Cl2 + H2O —– HClO(chloric acid) + HCl • Chlorine is both oxidised and reduced so is a disproportionation reaction. • The product mixture turns blue litmus paper red indicating the products are ACIDIC.

BENEFITS: - Bacteria in water are killed by the reactive oxygen atoms produced by the slow decomposition of chloric (I) acid: HClO —– HCl + O RISKS: - Chlorine gas is TOXIC. - Chlorinated hydrocarbons are carcinogenic and can form when alkanes react with chlorine to form a CHLORALKANE

MAKING HOUSEHOLD BLEACH : - Cold dilute sodium hydroxide is added to Cl2 at room temperature due to Cl2 being slightly soluble. Cl2 + 2NaOH —— NaCl + NaClO + H2O • Chlorine is both oxidised and reduced so it is a disproportionation reaction. • Household bleach is a solution of SODIUM CHLORIDE and SODIUM CHLORATE in a 1:1 molar ratio. • The chlorate ion kills bacteria • The product mixture is used to make STRONGER commercial bleach which is CHLORIC(I) acid or HYPOCHLOROUS acid, HClO

• SIMPLE MOLECULAR structures • Held together by LONDON FORCES between the diatomic molecules , X2.

STABILITY: - Stable, unlike their elements - They have a full outer shell of electrons USES: Sodium chloride NaCl ~ - used as a common salt Sodium fluoride NaF ~ - used in toothpaste to prevent tooth decay Calcium Fluoride CaF2 ~ - uses to make lenses which focus IR light

Use PRECIPITATION reactions: • Precipitates can be formed when two AQUEOUS solutions are mixed together. • A SOLID is formed as a result of a chemical reaction

1 ~ DISSOLVE unknown halide salt in water 2 ~ Add aqueous SILVER NITRATE (AgNO3) 3 ~ A SILVER HALIDE PRECIPITATE , AgX(s) , forms whose colour depends upon the halide ion present.

CHLORIDE: AgNO3(aq) + NaCl(aq)— AgCl(s) + NaNO3(aq) Ag+ (aq) + Cl- (aq) —- AgCl(s) Colour of precipitate ~ WHITE Addition of NH3 ~ precipitate is SOLUBLE in DILUTE ammonia. BROMIDE: AgNO3(aq) + NaBr(aq)— AgBr(s) + NaNO3(aq) Ag+ (aq) + Br-(aq) —— AgBr (s) Colour of precipitate ~ CREAM Addition of NH3 ~ precipitate is SOLUBLE in CONCENTRATED ammonia. IODIDE: AgNO3(aq) + NaI(aq) — AgI(s) + NaNO3(aq) Ag+ (aq) + I- (aq) —– AgI (s) Colour of precipitate ~ YELLOW Addition of NH3 ~ precipitate is INSOLUBLE in CONCENTRATED ammonia.