Group 7

Group 7

1. Reactivity and Displacement

   • Reactivity
     • Iodine, grey, solid
       • Bromine, red-brown, liquid
         • Chlorine, green, gas
           • Flourine, pale yellow, gas
     • Boiling points increase down group
       • Increases strength of overall V.D.W forces
         • As size and relative mass of molecules increases
           • Shown from changes in state decreasing in the group
     • Electronegativity decreases down the group
       • Larger atoms attract electrons less than small atoms
         • Electrons further from positive nucleus and shielded more
   • Displacement
     • Halogens displace less reactive halid ions from solution
       • A halogen will displace a halid in solution if the halid is below it on the p.table
         • Displacement reactions can be used to identify which halogen is in a solution
           • Br2 formed turns chlorine solution orange
             • I2 formed turns chlorine solution brown
               • I2 formed turns bromine solution brown

2. Test for Ions

3. Chlorine

   • Chlorine and Sodium Hydroxide makes bleach
     • Mix chlorine gas with cold, dilute, aqueous NaOH
       • To form sodium chlorate(I) solution - common in household bleach
         • 2NaOH + Cl2 -> NaClO + NaCl + H2O
           • 0 +1 -1
             • Cl oxi number goes up and down
               • Cl both oxidised and reduced, disproportionation
             • Sodium Chlorate has many uses, water treatment, bleaching paper and textiles, and cleaning products
           • ClO- is the chlorate(I) ion
   • Chlorine is used to kill bacteria in water
     • When chlorine is added to water it undergoes disporportionation
       • Produces a mixture of chloride ions and chlorate ions
         • Cl2 + H2O -> 2H^+ + Cl^- + ClO-
           • In sunlight, chlorine can decompose water to form chloride ions and oxygen
             • Cl2 + 2H2O -> 4H^+ + 2Cl^- + O2
               • Chlorate ions kill bacteria, add chlorine to water to treat it but chlorine is toxic
                 • Chlorine kills disease-causing microorganisms
                 • Some chlorine stays in water and prevents reinfection further in supply
                 • It prevents algae growth, eliminating bad tastes and smells
                 • Removes discolouration from organic compounds
                 • Chlorine is very harmful if breathed in
                 • Liquid chlorine can cause severe chemical burns
                 • Chlorine can react with organic compounds forming chlorinated hydrocarbons
                   • These are carcinogenic, but cancer risk is small compared to untreated water risk

4. Halides

   • Reducing power of halides increases down the group
     • To reduce something halide needs to lose electron
       • Down the group the attraction to the outer electrons get weaker
         • Ions get bigger, electron further away from positive nucleus
           • Extra inner electron shells so theres greater shielding
             • Down the group its eaiser to lose the electron
   • All halides react with concentrated sulfuric acid to give hydrogen halide
     • When reacting NaF or NaCl + H2SO4
       • Forms HF or HCl gas - may see fumes as gas contact with air
       • HF/HCl not strong enough to reduce H2SO4 so reaction stops
       • Not a redox reaction as oxi state stays same for halide sulfur
       • When reacting NaBr with H2SO4
         • Similar to above, produces misty fumes of HBr
         • HBr is strong enough to react with H2SO4 in a redox reaction
         • This produces choking fumes of SO2 and orange fumes of Br2
         • When reacting NaI with H2SO4
           • Again similar producing HI gas
           • Again HI reduces H2SO4 to produce solid I2, SO2 and water
           • HI is so strong it continues to reduce the newly formed SO2
           • Produces H2S, more solid Iodine and water
   • Test for Halides
     • First add dilute nitric acid to remove unwanted ions
       • Then drops of silver nitrate solution (AgNO3)
         • If halide, precipitate should form
           • Ag^+(aq) + X^-(aq) -> AgX(s)
             • Can make sure by adding ammonia solution
               • Each silver halide (AgX) has different solubility
                 • F - No ppt
                   • Cl - Forms white ppt slowest, dissolves in dilute NH3, most soluble
                     • Br - Cream ppt, dissolves in conc NH3
                       • I - Forms yellow ppt fastest, insoluble in conc NH3, least soluble

Imagens e arquivos do mapa