group 7 Flashcards
fluorine at room temp
pale yellow gas
chlorine at room temp
greenish gas
bromine at room temp
orange/ brown liquid
iodine
black solid which vaporises on heating to a purple gas
why are fluorine properties unusual compared to other halogens
F-F covalent bond is suprisngly weak as the atoms are very small so the non bonding electrons on the outer shells are held so close to one another that they start to repel each other
trend in size of atoms down group 7
the get bigger as the elements have another electron shell
trend in Mp and Bp in group 7
non polar diatomic molecules with induced dipole dipole forces
strength of these depend on size of the molecule and so F2 has the lowest MP AND BP and I2 has the highest
halogens are ……… agents
OXIDISING
oxisidising power ……. down group 7
decreases
describe a halogen displacement reaction
the element highest up group 7 should form a halide ion whereas the halogen lowest down group 7 should form a halogen molecule
HALIDE IONS ARE ……… AGENTS
reducing
reducing power ……… down group 7
increases
test for halide ions
add nitric acid to remove carbonate ions
add silver nitrate and observe
F- clear and colourless
Cl- white precipitate
Br- cream precipitate
I- yellow precipitate
double checking halide ions test and
addd ammonia
white precipate for Cl- will dissolve in dilute ammonia
cream precipitate for Br- won’t dissolve in dilute ammonia but will dissolve in concentrated ammonia
yellow precipitate I- is insoluble in concentrated and dilute ammonia
use of chlorine
treatment of drinking water and swimming pools
in low concentrations chlorine is safe for humans but can kill bacteria
