All toxic All form Diatomic molecules All form ionic salts Halogens Group VII All toxic All form Diatomic molecules All form ionic salts

How does the trend in atomic radius dictate: (i) The trend in boiling points?

Boiling points of Halogens

Boiling points of Halogens

How does the trend in atomic radius dictate: (ii) The ability of the halogens to act as an oxidising agent?

GROUP 7 : THE HALOGENS Halogen Symbol Formula State at 298K Colour Fluorine Chlorine Bromine Iodine Astatine F Cl Br I At F2 Cl2 Br2 I2 At2 Gas Liquid Solid Pale yellow Green Dark red Dark grey Black

Fluorine F [He]2s22p5 Chlorine Cl [Ne]3s23p5 Bromine Br [Ar]3d104s2 4p5 Iodine I [Kr]4d105s2 5p5 Astatine At [Xe]4f14 5d106s2 6p5

Halogens are powerful oxidising agents All halogens gain electrons to make halide ions, so all the halogens are oxidising agents. You need to know the trend in the oxidising power as you go down group VII. Chlorine atoms gain an electron to make chloride ions: Cl2 + e- g 2Cl- The chlorine atom has gained an electron so is reduced, so the chlorine atom is an oxidising agent (oxidising agents are electron acceptors).

Down the group the halogens become weaker oxidising agents Down the group the halogens become weaker oxidising agents. Also the halide ions become stronger reducing agents.

Cl2(g) + 2KBr(aq) g Br2(aq) + 2KCl(aq) +1 -1 +1 -1 Cl2(g) + 2KBr(aq) g Br2(aq) + 2KCl(aq) Green gas Colourless solution Red-brown solution Colourless solution Write in the oxidation numbers to show what is being oxidised and reduced. Chlorine is being reduced (and is the oxidising agent) Also what are the oxidation and reducing agents? Bromine is being oxidised (and is the reducing agent) Br2(l) + 2KCl(aq) g No reaction

HALOGENS - DISPLACEMENT REACTIONS KCl(aq) KBr(aq) KI(aq) Cl2(aq) No Reaction Pale Green Solution Cl2(aq) + 2Br-(aq)g 2Cl-(aq) + Br2(aq) Orange Solution Cl2(aq) + 2I-(aq)g 2Cl-(aq) + I2(aq) Brown Solution Br2(aq) Br2(aq) + 2I-(aq)g 2Br-(aq) + I2(aq) I2(aq)

Aqueous halogens in cyclohexane Halogens are non-polar molecules. They will therefore dissolve best in non-polar solvents, like cyclohexane. Cyclohexane will not mix with water so two distinct layers will form. Cyclohexane layer Aqueous layer Cl2(aq) Br2(aq) I2(aq)

Bromine water (aqueous bromine, Br2) is shaken with a volume of cyclohexane, and then the follow aqueous solutions are added to separate portions. a) Aqueous sodium iodide b) Aqueous chloride c) Aqueous sodium astatide The orange cyclohexane layer would turn purple Br2(aq) + 2I-(aq) g 2Br-(aq) + I2(aq) No change Given its position in group VII, we would expect astatine to be darker in colour than iodine . The orange cyclohexane layer would turn this colour. Br2(aq) + 2At-(aq) g 2Br-(aq) + At2(aq) Each mixture is shaken again. Describe what you would expect to see. Write equations for any reactions that would occur.

Cl2(aq) + H2O(l) g HCl(aq) + HClO(aq) When chlorine reacts with water a mixture of hydrochloric acid (HCl) and chloric (I) acid (HClO) is formed Cl2(aq) + H2O(l) g HCl(aq) + HClO(aq) Use oxidation numbers to deduce what atom is being oxidised and what is being reduced. The reaction is a dispropotionation because chlorine is both oxidised and reduced

Reaction of chlorine with aqueous sodium hydroxide Cl2(aq) + 2NaOH(aq) g NaCl(aq) + NaClO(aq) + H2O(l) NaClO is sodium chlorate (I), also called sodium hypochlorite. A dilute sodium chlorate (I) is a key ingredient of chlorine-based household bleaches.

Bromine reacts with cold dilute alkali to give a colourless solution containing Br- and BrO- ions. Write a balanced chemical equation for this reaction What are the oxidation states of bromine before and after the reaction c) Name this type of reaction. Br2 + 2NaOH g NaBr + NaOBr + H2O 0 before, -1 and +1 after disproportionation

TESTING FOR HALIDES – AgNO3 • make a solution of the halide • acidify with dilute nitric acid - prevents the precipitation of other salts • add a few drops of silver nitrate solution • treat any precipitate with dilute ammonia solution • if a precipitate still exists, add concentrated ammonia solution

TESTING FOR HALIDES – AgNO3 CHLORIDE white ppt of AgCl soluble in dilute ammonia BROMIDE cream ppt of AgBr insoluble in dilute ammonia but soluble in conc. IODIDE yellow ppt of AgI insoluble in dilute and conc. ammonia solution

TESTING FOR HALIDES – AgNO3 CHLORIDE white ppt of AgCl soluble in dilute ammonia BROMIDE cream ppt of AgBr insoluble in dilute ammonia but soluble in conc. IODIDE yellow ppt of AgI insoluble in dilute and conc. ammonia solution halides precipitate as follows Ag+(aq) + X¯(aq) ——> Ag+X¯(s) when they dissolve in ammonia a colourless diammine complex is formed [Ag(NH3)2]+(aq)

TESTING FOR HALIDES – AgNO3 CHLORIDE BROMIDE IODIDE PLACE A SOLUTION OF THE HALIDE IN A TEST TUBE

TESTING FOR HALIDES – AgNO3 ADD SOME DILUTE NITRIC ACID CHLORIDE BROMIDE IODIDE ADD SOME DILUTE NITRIC ACID

TESTING FOR HALIDES – AgNO3 ADD SILVER NITRATE SOLUTION CHLORIDE BROMIDE IODIDE ADD SILVER NITRATE SOLUTION WHITE PRECIPITATE OF SILVER CHLORIDE AgCl CREAM PRECIPITATE OF SILVER BROMIDE AgBr YELLOW PRECIPITATE OF SILVER IODIDE AgI

TESTING FOR HALIDES – AgNO3 ADD DILUTE AMMONIA SOLUTION CHLORIDE BROMIDE IODIDE ADD DILUTE AMMONIA SOLUTION WHITE PRECIPITATE OF SILVER CHLORIDE - SOLUBLE CREAM PRECIPITATE OF SILVER BROMIDE - INSOLUBLE YELLOW PRECIPITATE OF SILVER IODIDE - INSOLUBLE

TESTING FOR HALIDES – AgNO3 ADD CONCENTRATED AMMONIA SOLUTION CHLORIDE BROMIDE IODIDE ADD CONCENTRATED AMMONIA SOLUTION WHITE PRECIPITATE OF SILVER CHLORIDE - SOLUBLE CREAM PRECIPITATE OF SILVER BROMIDE - SOLUBLE YELLOW PRECIPITATE OF SILVER IODIDE - INSOLUBLE

a) What would you expect to be the physical state of astatine at room temperature. Explain your answer b) Fluorine and chlorine both react with sodium metal to form a salt. i) Write a balanced equation for each reaction ii) Which of the two reaction will be most vigorous. Why? iii) What structure and bonding will the products have? c) What is the oxidation number of chlorine in Cl2, CaCl2, Cl2O7 and ClO2? Solid. At2 molecules are larger than I2 molecules (At2 molecules have more elctrons than I2 molecules) therefore van der Waals’ forces will be stronger. Iodine is a solid at room temperature, therefore so is astatine Cl2 + 2Na g 2NaCl F2 + 2Na g 2NaF The fluorine reaction. Fluorine is more reactive than chlorine as it has a smaller atomic radius. This means it is easier for an incoming electron to enter its outer shell as it has experiences less shielding and is closer to the nucleus. Both are giant ionic 0, -1, +7, +4

203.3 g White precipitate/goes white

Ag+(aq) + Cl-(aq) g AgCl(s) AgCl dissolves in NH3(aq) AgBr dissolves in conc NH3(aq)/partially soluble in NH3(aq) AgI insoluble in NH3(aq) or conc NH3(aq) White precipitate/goes white