Group 17 Flashcards
Name the state and colour of each halogen under standard conditions.
F2: pale yellow gas
Cl2: green-yellow gas
Br2: orange-brown liquid
I2: grey-black solid
Describe the trend of volatility in group 17
Decreases down the group.
Halogens are simple molecules held together by weak van der Waals’ forces, instantaneous dipole-induced dipole. Down the group, there’s an increase in electrons. Therefore the id-id forces are stronger, and it is harder for the molecules to separate.
Describe the general trend of bond enthalpy in group 17, including the exception.
Bond enthalpy generally decreases down the group.
Halogens are covalently bonded diatomic molecules by overlapping orbitals.
Down the group, atomic radius increases due to increasing principle quantum shells. This makes the nucleus further from bonding pair of electrons, weakening their attraction.
Fluorine is the exception because their atomic radii is so small that lone pairs get close enough to cause repulsion between the two atoms. Weakening the bonds and making F2 have a lower bond enthalpy than Cl2 and Br2.
Describe the oxidising nature of halogens
Oxidising agents (accepts an electron) and are reduced (-)
Describe the trend of oxidising power in halogens
Oxidising power decreases down the group.
Electronegativity decreases down the group, so it gets harder for halogens to accept electrons (be reduced) down the group due to weaker positive charge from shielding with increasing atomic radii.
How can displacement reactions occur with halogens and another halide compound?
If the halogen is more reactive than the halide in the compound.
E.g: 2NaBr + Cl2 -> 2NaCl + Br2
Describe the trend of thermal stability in hydrogen halides
Thermal stability decreases down the group.
Atomic radius increases down the group, forming longer bond lengths with hydrogen. This causes the bonding electrons to be further from the positive nucleus, weakening their attraction and making it easier to break the bond using heat.
Describe the reducing nature of halogens
Reducing agents (donates electrons) and are oxidised (+)
Describe the trend of reducing power in halogens
Reducing power increases down the group.
Halide (-) ionic radius increases down the group, weakening the attraction between nucleus and valence electrons due to distance. Making it easier to be oxidised (lose electrons) down the group.
Results of halogens when tested with silver nitrate.
AgCl: white precipitate
AgBr: cream precipitate
AgI: yellow precipitate
Describe the solubility of silver halides in ammonia
AgCl dissolves in dilute ammonia
AgBr only dissolves in conc. ammonia
AgI does not dissolve in ammonia at all
NaCl reducing conc. sulfuric acid and the observations
H2SO4 (l) + NaCl (s) -> HCl (g) + NaHSO4 (s)
* HCl appears as white fumes
NaBr reducing conc. sulfuric acid, and the observations (reducing 2 times)
H2SO4 (l) + NaBr (s) -> HBr (g) + NaHSO4 (s)
2HBr (g) + H2SO4 (l) -> Br2 (g) + SO2 (g) + 2H2O (l)
* Br2 appears as reddish-brown gas
NaI reducing conc. sulfuric acid, and the observations (reducing 4 times)
H2SO4 (l) + NaI (s) -> HI (g) + NaHSO4 (s)
2HI (g) + H2SO4 (l) → I2 (g) + SO2 (g) + 2H2O (l)
* I2 appears as purple vapour
6HI (g) + H2SO4 (l) → 3I2 (g) + S (s) + 4H2O (l)
* S appears as a yellow solid
8HI (g) + H2SO4 (l) → 4I2 (g) + H2S (s) + 4H2O (l)
* H2S produces a smell of bad eggs
Define disproportionation reaction
When the same species in a reaction is both oxidised and reduced (lose and gain electron)
