ES 1 Flashcards
what is the appearance of halogens in an polar solvents (water)
chlorine - pale green
bromine - yellow/orange
iodine - brown
what is the appearance of halogens in non-polar solvents (cyclohexane)
chlorine - pale green
bromine - red/brown
iodine - violet/purple
features of group 7 elements
called halogens
7 electrons on the outer shell
most reactive non-metal group
all occur as diatomic molecules
not found naturally in element form
found naturally in compounds
reactivity decreases down the group
what are diatomic molecules joined by
single covalent bond
features of ionic bonding of halogens
gain an electron from a metal atom
form halide ion in an ionic compound
halogen becomes stable
halogen becomes X- ion
features of covalent bonding in halogens
share electron from another non-metal atom Br2, F2, I2 (diatomic)
what are the trends of properties down group 7
become darker in colour (pale yellow, pale green, orange, purple, shiny black)
melting and boiling points increase
changes state down group -
gas - gas - liquid - solid - solid
what are the chemical properties of the halogens
oxidising agents (remove electrons form other elements to complete their outer shell)
why is fluorine the strongest oxidising agent
fluorine atoms are small so the attraction from the nucleus to the extra electron needed to complete full outer shell is strong
electron shielding increases down the group so attraction from nucleus is weaker to electrons
atomic radius increases down the group (more shells/shielding) makes it more difficult to attract the needed electron
explain what reaction this is, why it occurs and how it can be simplified
Cl2 (aq) + 2KI (aq) —- 2KCl (aq) + I2 (aq)
reaction is a displacement reaction
chlorine is more reactive that iodide so has displaced it
halide solutions are colourless so a if a colour change occurs then a displacement reaction has happened
explanation why -
Cl is above I in group 7 so is more reactive
each iodide ion loses an electron and is oxidised
each chlorine atom gains and electron so is reduced
chlorine is the oxidising agent
how it can be simplified-
Cl2 (aq) + 2I- (aq) —- 2Cl- (aq) + I2 (aq)
(pale green) (brown)
K+ ions are spectator ions as they are in the same state after the reaction so can be removed (no effect on reaction)
what is used to test for silver halide ions
silver nitrate since its insoluble
what is the name of the reaction to test for halide ions
precipitate reaction (silver precipitate is formed)
what is the definition of a precipitate reaction
formation of a solid from a solution during a chemical reaction
precipitates are often formed when two aqueous solutions undergo a chemical reaction
halide ion test results (equation and precipitate colour)
chloride-
Ag+ (aq) + Cl- (aq) —- AgCl (s) white precipitate
bromide-
Ag+ (aq) + Br- (aq) —- AgBr (s) cream precipitate
iodide-
Ag+ (aq) + I- (aq) —- AgI (s) yellow precipitate
what is added to distinguish between precipitate colours and why
aqueous ammonia (NH3 (aq))
this is because the silver halides have different solubilities in aqueous ammonia
