Group 7 Flashcards
Physical state of Fluorine and Chlorine
Gases at RTP.
Physical state of Bromine
Liquid at RTP.
Physical state of iodine
Solid at RTP.
The mpt and bpt increases down the group, because:
- Number of electrons increase, so greater uneven electron distribution.
- Stronger induced dipole-dipole attractions between molecules.
- So, more energy is required to break the attractions between molecules.
- Hence, boiling and melting point increases.
Definition of volatility
The ease at which a liquid turns into a gas.
Volatility decreases down the group, because:
- An increase in the number of electrons.
- Increases the uneven distribution of electrons.
- Stronger induced diploe-dipole forces.
- Hence, the volatility decreases.
Reactivity decreases down a group, because:
- Down the group, the atoms have more electron shells.
- More shielding of nuclear charge.
- Less nuclear attraction for incoming electrons.
- Electrons gained by chlorine more easily than by iodine.
This means that chlorine has a greater electron affinity for electrons than bromine or iodine.
Defintion of electron affinity
Ability of an element to gain an electron.
Definition of oxidising power
This is the ability of an atom or species to oxidise another species (take an electron from it).
Halide ion sin solution are…
colourless.
Chlorine colour in water…
Pale green
Chlorine colour in cyclohexane…
Pale green
Bromine colour in water…
Orange
Bromine colour in cyclohexane…
Orange
Iodine colour in water…
Brown
Iodine colour in cyclohexane…
Purple
Ionic equ, full equ and obs between chlorine and bromine
Cl2(g) + 2Br-(aq) …. Br2(l) + 2Cl-(aq)
Cl2(g) + 2NaBr(aq) …. Br2(l) + 2NaCl(aq)
Obs: pale green to orange (aq or cyclohexane).
Ionic equ, full equ and obs between chlorine and iodine
Cl2(g) + 2I-(aq) …. I2(s) + 2Cl-(aq)
Cl2(g) + 2NaI(aq) …. I2(s) + 2NaCl(aq)
Obs: Pale green to brown (water) OR orange to purple (cyclohexane).
Ionic equ, full equ and obs between bromide and iodine
Br2(l) + 2I-(aq) …. 2Br(l) + I2(s)
Br2(l) + 2NaI(aq) …. 2NaBr(aq) + I2(s)
Obs: orange to brown (water) OR orange to purple (cyclohexane).
The more reactive halogen takes electrons from the less reactive halide (oxidises it). This is because:
Chlorine has less electron shells than Br-/I-.
Chlorine has less sheilding.
Chlorine has more nuclear attraction for incoming electrons.
Chlorine takes electrons from Br-/I-.
To prove the reactivity trend, use…
- Cl2 + Br-
- Br2 + I-
Obs for chloride and acidified silver nitrate…
White precipitate
Equ for chloride and acidificed silver nitrate…
Ag+(aq) + Cl-(aq) …. AgCl(s)
Obs for bromide and acidified silver nitrate…
Cream precipitate
Equ for bromide and acidified silver nitrate
Ag+(aq) + Br-(aq) …. AgBr(s)
Obs between iodide and acidified silver nitrate
Yellow precipitate
Equ between iodide and acidified silver nitrate
Ag+(aq) + I-(aq) …. AgI(s)
Chloride and dilute ammonia solution
AgCl(s) dissolves
Bromide and dilute ammonia solution
AgBr(s) remains
Bromide and concentrated ammonia solution
AgBr(s) dissolves
Iodide and dilute ammonia solution
AgI(s) remains
Iodide and concentrated ammonia solution
AgI(s) remains (turns white)
Silver fluoride and water
No precipitate formed as silver fluroride is soluble in water
Chlorine and water equ
Cl2(g) + H2O(l) ….HClO(aq) + HCl(aq)
Explain the change in oxidation numbers for the chlorine and water equ
Chlorine is oxidised as the oxidation number increases from 0 in Cl2 to +1 in HClO.
Chlorine is reduced as the oxidation number decreases from 1 in Cl2 to -1 in HCl, so this is reduction.
This is an example of a disproportionation reaction.
Definition of disproportionation reaction
The same element is both oxidised and reduced.
Use for the reaction between water and chlorine
Used to kill bacteria in water. The HClO forms reactive oxygen atoms that destroy bacteria in the water.
Chlorine and dliute NaOH(aq) equ
Cl2(g) + 2NaOH(aq) …. NaClO + NaCl(aq) + H2O(l)
Explain the change in oxidation numbers for chlorine and dilute NaOH(aq) equ
Chlorine increases in oxidation number from 0 in Cl2 to +1 in NaClO, so chlorine has been oxidised.
Chlorine has decreased in oxidation number from 0 in Cl2 to -1 in NaClO, so chlorine has been reduced.
Use for the reaction between chlorine and dilute NaOH(aq)
Used in the production of bleach. The active ingredient is NaClO(aq); sodium chlorate (I).
