3.1.3: The halogens Flashcards
Test for halide ions
Add a few drops of aqueous silver nitrate
Results for halide ions test
Chloride - white ppt
Bromide - cream ppt
Iodide - yellow ppt
Add what to halide ppt as a further test?
Aqueous ammonia
Results of adding aqueous ammonia to halide ion ppt?
Chloride - white ppt - dissolves in dilute ammonia
Bromide - cream ppt - dissolves in aqueous ammonia
Iodide - yellow ppt - does not dissolve even in conc NH3
Displacement of halogens method
- Add an aqueous solution of the halogen
- To an aqueous solution of the halide
- Record the colour of the top (displaced) layer
e.g. KBr⁻ + Cl₂ –> 2KCl + Br₂
Ionic equation for halide ions test
Ag+ + X- —> AgX
Displacement of halogens - test results
- Organic layer orange - bromine has been displaced
* Organic layer violet/purple - iodine has been displaced
Displacement of halogens - most reactive to least reactive
Most = chlorine
Bromine
Least = Iodine
Reactivity of Group 7 elements __________ down group
decreases
Why does reactivity of Group 7 elements decrease down group?
- Larger atomic radius, more shielding means reduced force of positive charge felt by outermost shell of e-
- Harder to attract electron to outer shell (lower e- affinity)
- Less reactive
Boiling point _______ down Group 7
increases
Why does boiling point increase down Group 7?
- Greater n(e-)
* Greater London forces between molecules
Bond enthalpy _______ down Group 7
decreases
Why does bond enthalpy decrease down Group 7?
- Halogen atom gets larger so X-X bond gets longer and weaker
- Fluorine is anomalous –> so small that e- repel
Electronegativity ______ down Group 7
decreases
