Group 7 Flashcards
Fluorine
very pale yellow gas. It is highly reactive
Chlorine
greenish, reactive gas, poisonous in high concentrations
Bromine
red liquid, that gives off dense brown/orange poisonous fumes
Iodine
shiny grey solid sublimes to purple gas.
MP and BP
Increase down the group
As the molecules become larger they have more electrons and so have larger van der waals forces between the molecules. As the intermolecular forces get larger more energy has to be put into break the forces. This increases the melting and boiling points.
Electronegativity
As one goes down the group the electronegativity of the elements decreases.
As one goes down the group the atomic radii increases due to the increasing number of shells. The nucleus is therefore less able to attract the bonding pair of electrons.
Oxidising ability
The oxidising strength decreases down the group. Oxidising agents are electron acceptors.
Oxidation equations
Cl2(aq) + 2Br – (aq) -> 2Cl – (aq) + Br2(aq)
Cl2(aq) + 2I – (aq) -> 2Cl – (aq) + I2(aq)
Br2(aq) + 2I – (aq) -> 2Br – (aq) + I2(aq)
Reducing ability
The halides show increasing power as reducing agents as one goes down the group. This can be clearly demonstrated in the various reactions of the solid halides with concentrated sulfuric acid
F and Cl in reduction of H2SO4
Step 1
NaF(s) + H2SO4(l)->NaHSO4(s) + HF(g)
Observations: White steamy fumes of HF are evolved.
NaCl(s) + H2SO4(l)->NaHSO4(s) + HCl(g) Observations: White steamy fumes of HCl are evolved.
Acid-base reactions
Bromide Step 2
2 H+ + 2 Br - + H2SO4 ->Br2(g) + SO2(g) + 2 H2O(l)
White steamy fumes of HBr are evolved.
orange fumes of bromine are also evolved and a colourless, acidic gas SO2
H2SO4= Oxidising agent
Iodide
NaI(s) + H2SO4(l)->NaHSO4(s) + HI(g)
2 H+ + 2 I- + H2SO4->I2(s) + SO2(g) + 2 H2O(l)
6H+ +6I- +H2SO4 ->3I2 +S(s)+4H2O(l)
8H+ +8I- +H2SO4->4I2(s) + H2S(g) + 4H2O(l)
Iodide observations
White steamy fumes of HI are evolved. Black solid and purple fumes of Iodine are also evolved
A colourless, acidic gas SO2
A yellow solid of sulfur
H2S (Hydrogen sulfide), a gas with a bad egg smell,
Identifying halide ions
silver nitrate
The test solution is made acidic with nitric acid, and then silver nitrate solution is added dropwise.
The role of nitric acid is to react with any carbonates present to prevent formation of the precipitate Ag2CO3. This would mask the desired observations
Nitric acid results
Cl white
Br Cream
Iodide pale yellow
