Group 17 Flashcards
Colour and state of the halogens
F2 is a yellow gas.
Cl2 is a greenish yellow gas.
Br2 is an orange liquid.
I2 is a grey black solid.
At is a black solid.
Trend of volatility down the group
The halogens become less volatile down the group. The number of electrons increases down the group thus increasing the id-id attraction between molecules
Describe the bond strength of halogens as we move down the group
Bond strength decreases down the group . As atomic radius increases down the group, the covalent bond strength decreases. F-F is an exception in this list. This is due to the small size of F atoms. The F-F bond length is so short the lone pairs of electrons on the atoms repel each other and weaken the bond.
Explain the reactivity of the halogens as oxidising agents
Oxidising strength decreases down the group. The electron affinity of the elements decrease down the group as the atomic radius increases, the incoming electron is further from the electron thus less strongly held. Also, atomisation energy decreases since bond energy decreases. Hydration energy decreases as the radius of the halide ions increases down the group
Reaction of F2 with hydrogen
Reacts explosively in the dark
Reaction of Cl2 with hydrogen
Reacts explosively in sunlight or a flame
Reaction of Br2 with hydrogen
Reacts slowly on heating
Reaction of I2 with hydrogen
Forms an equilibrium mixture on heating
Describe the thermal stabilities of hydrogen halides
Hydrogen halides become less stable to heat down the group. HF and HCl are very stable to heat, they do not split up into their respective elements if heated to any normal lab temperature. HBr splits slightly into H2 and br2 on heating and HI splits to a greater extent. As atomic radii of the halogens increases, the covalent bond length increases, thus making the bond weaker.
Relative reactivity of halide ions as reducing agents
The halides become stronger reducing agents down the group. The E values become less negative down the group, hence with a strong enough oxidising agent, the halide ions can be oxidised more easily when moving down the group
Reaction of Cl- with sulphuric acid (acid-base)
Steamy white fumes of HCl are seen.
NaCl + H2SO4 —> HCl + NaHSO4
Reaction of Br- with sulphuric acid (acid-base)
NaBr + H2SO4 —> HBr + NaHSO4
Reaction of Br- with sulphuric acid (redox)
H2SO4 + 2H+ + 2BR- —> Br2 + SO2 + 2H2O
Reaction of I- with sulphuric acid (acid-base)
H2SO4 + NaI —> HI + NaHSO4
Reaction of I- with sulphuric acid (redox)
H2SO4 + 8H+ + 8I- —> 4I2 + H2S +4H2O
Lots of purple iodine vapour
