3.2.3 Group 7(17), the halogens Flashcards
describe the appearance of all of the halogens at room temp
. F is pale yellow gas
. Cl is a green gas
. Br is a red brown liquid
. I is a black/grey solid
describe the trend in atomic radius down the group
increases as number of main electron shells/levels increases
describe the trend in electronegativity down the group
decreases going down the group, as outer electrons get further away from + nucleus and so become more shielded and less attracted
describe the trend in mp/bp down group - group 7
increases - larger atoms mean larger molecules and so larger VDWs between molecules, which require more energy to overcome
how does the oxidising ability of the halogens change down the group
. decreases down group
. oxidising agents become reduced and agin electrons
. easier when smaller and outer level is less shielded
. so Fluorine is the most powerful oxidising agent
- effects displacement reactions
how will halogens react with metal halides
. a halogen will displace a less reactive metal from its metal halide in an aqueous solution
. eg. Cl2 + 2NaBr —> Br2 + 2NaCl
. can’t investigate Fluorine as it reacts with water
. Cl oxidises 2Br- to Br2, so Cl is the oxidising agent
what’s the difference between halogens and halides
halogens are the molecule, halides are the IONS!
what is the trend in the reducing power of the halides (halogen ions)
increases down the group, larger atoms have more shielded outer shells so more easily lose electrons
describe the reaction of solid sodium chloride with concentrated sulphuric acid
. drops of conc H2SO4 added to the solid
. NaCl + H2SO4 –> NaHSO4 + HCl
. steady fumes of hydrogen chloride seen, and the product is sodium hydrogensulphate
. NOT a redox reaction as no oxidation states change, chloride ion too weak of a reducing agent
. similar reaction occurs with NaF
describe the reaction of solid sodium bromide with concentrated sulphuric acid
2 reactions occur
acid base reaction
. first is the same as with NaCl but produces NaHSO4 and HBr
. but Br- ions are strong enough reducing agents to reduce the acid to SO2
. so 2H+ + 2Br- + H2SO4 –> SO2 + 2H2O + Br2 occurs as well
. second reaction is a redox reaction and both are exothermic
. steamy fumes of HBr seen as well as brown fumes of bromine
describe the reaction of solid sodium iodide with concentrated sulphuric acid
same reactions as with chloride and bromide ions
. but iodine is an even stronger reducing agent than Br
. so 8H+ + 8I- + H2SO4 –> H2S + 4H2O + 4I2
. so will see, overall, steady fumes of hydrogen iodide, black solid iodine, bad egg smell of H2S, colourless SO2 formed and some yellow sulphur
. sulphur formed when sulphur reduced from +6 to -2 and when it passes through oxidation state of 0 some solid sulphur may be formed
how can you identify halide ions
react them with silver nitrate (to get silver ions) to form silver halide precipitates (apart form fluorine because its precipitate is soluble and will dissolve in water)
. first add dilute HNO3 to remove impurities such as carbonate or hydroxide ions which would interfere by forming other products like silver carbonate or hydroxide
. then add a few drops of silver nitrate
describe the results for the halide ions test
. AgF forms no precipitate
. AgCl forms a white precipitate
. AgBr forms a cream precipitate
. AgI forms a yellow precipitate
. to further distinguish (usually between Br an I)
add some drops of conc NH3 solution and silver Cl and Br will dissolve, but silver I won’t
how does chlorine react with water
. Cl2 + H2O <—> HClO + HCl this is a reversible reaction to from chloric acid and HCl, this is a disproportionation reaction so chlorine is both oxidised and reduced. This reaction takes place in pools and to purify drinking water as chloric acid kills bacteria by oxidation
2. in sunlight 2Cl2 + 2H2O –> 4HCl + O2 occurs. Chlorine rapidly lost from shallow pools in sun so they frequent addition of chlorine
how does chlorine react with sodium hydroxide
Cl2 + 2NaOH –> NaClO + NaCl + H2O
. forms sodium chlorate which is an oxidising agent and an ingredient in bleach
. also a disproportionation reaction
