group 7 Flashcards
(44 cards)
how does atomic radius change down group 7?
increases
how does melting and boiling point change down the group?
increases- the atoms increase in size, as they gain extra electron shells, and the intermolecular forces become stronger.
how does electronegativity change down the halogens?
decreases
how does first ionisation energy change down the group?
decreases
what is the state of chlorine at room temperature and how does it appear at room temp, aqueous solution and in cyclohexane?
gas at room temp
green gas
pale green solution
pale green in cyclohexane
what state and colour is flourine at room temp?
pale yellow gas
what state at room temp and colour at room temp, in aqueous solution and in cyclohexane is bromine?
liquid at room temp
red-brown liquid room temp
orange in solution
orange in cyclohexane
what is the state at room temp, and colour at room temp, in solution and in cyclohexane for ioidine?
solid at room temp
black solid
brown in solution
purple in cyclohexane
where are the halogens more soluble?
in non-polar solvents (like cyclohexane) than in water, because the halogens are non-polar
the solubility in water decreases down the group as the halogen molecule becomes larger
the redox reactions of the halogens are displacement reactions, what is this evidence for?
the trend in oxidising powers of the halogens
describe the colour change when reacting chlorine aq (pale green) with colourless KBr aq, and then followed by cyclohexane and KBr?
why does this occur?
orange both times due to Br2
chlorine displaces bromine as a strong oxidising agent
describe the colour change when chlorine aq reacts with colourless KI aq, followed by cyclohexane and KI?
why?
brown in Cl2
purple in cyclohexane
chlorine displaces iodine as a strong oxidising agent
describe the colour change when bromine aq (orange) reacts with colourless KCl aq , followed by cyclohexane and KCl?
no change both times (stays orange)
bromine doesn’t displace chlorine because it isn’t as strong of an oxidising agent
describe the colour change when bromine aq (orange) reacts with colourless KI aq, followed by cyclohexane and KI?
brown in bromine
purple in cyclohexane
bromine displaces iodine because it is a stronger oxidising agent
describe the colour change when iodine aq (brown) reacts with KCl, followed by cyclohexane (purple) and KCl?
no change both times
because iodine doesn’t displace chlorine because it isn’t as strong of an oxidising agent
describe the colour change when iodine aq (brown) reacts with KBr, followed by cyclohexane with KBr?
no change both times
because iodine doesn’t displace bromine because it isn’t as strong of an oxidising agent
what is an oxidising agent and why are halogens oxidising agents?
a substance which gains electrons
halogens are oxidising agents because they gain electrons to form halide ions
X2 + 2e- ————-> 2X-
what is the trend of oxidising power down group 7? why?
decreases
because;
-more shells and more shielding down group
-therefore ability to gain electrons is less as nuclear attraction decreases
what is the method for the experiment to determine oxidising power of the halogens?
-add a solution of each halogen to a solution of each potassium halide in turn
-note any colour change and decide whether a reaction has occurred
-add cyclohexane ( a non-polar solvent) and note the colour in the organic (top) layer, this will tell you which halogen is now present
what is a reducing agent? how can halide ions act as reducing agents?
a substance which donates electrons
halide ions can act as reducing agents because they can donate electrons to form halogens
2X- ———–> X2 + 2e-
how does reducing strength change down group 7? why?
increases
because:
-more shells so shielding increases down group
-easier to lose an electron because the nuclear charge decreases
what are the strongest oxidising and reducing agents?
oxidising; flourine
reducing; iodine
what is the oxidation number of sulfur in conc sulfuric acid before it is reduced by a halide ion?
+6
how can we test for sulfate ions using the halides?
using barium chloride and a white ppt forms
