Group 7 (Halogens) Flashcards
Explain the trend in boiling point as you go down the group
Increases down the group
Atomic radius increases with electron shielding
Stronger Van der Waals between molecules
Takes more energy to break
Explain the trend in electronegativity (EN) down the group
Decreases down the group
More electron shielding
Outer electrons further away from positive nucleus
Less attraction between nucleus and electron pair in covalent bond
What do you use to test for halide ions?
Acidified silver nitrate / AgNO3
What is the result and ionic equation for each of the 3 halides to acidified AgNO3?
Chlorine = white ppt
Ag+ + Cl- —> AgCl
Bromine = cream ppt
Ag+ + Br- —> AgBr
Iodine = yellow ppt
Ag+ + I- —> AgI
What happens to the solubilities of each of the silver halide solutions when ammonia / NH3 is added?
AgCl dissolves in both dilute and concn NH3
AgBr dissolves in only concn NH3
AgI does not dissolve in either
Explain the trend in oxidising ability down the group
Decreases down the group
Chlorine has fewest electron shells
Greatest attraction between outer shell and nucleus
Easiest to gain electrons / be reduced
Therefore best oxidising agent
Explain the trend in reducing ability down the group
Increases down the group
Iodine has the most electron shells
Weakest attraction between outer shell and nucleus
Easiest to lose electrons / be oxidised
Therefore best reducing agent
What are the 4 equations with iodine reducing sulfuric acid?
H2SO4 + 2 I- —> SO4(2-) + I2
H2SO4 + 2 I- + 2 H+ —> SO2 + I2 + H2O
(SO2 = choking gas)
H2SO4 + 6 I- + 6 H+ —> S + 3 I2 + 4 H2O
(S = yellow solid)
H2SO4 + 8 I- + 8 H+ —> H2S + 4 I2 + 4 H2O
(H2S = rotten eggs)
Why is chlorine added to drinking water?
Forms chlorate (I) / ClO- ions which kill any microorganisms
Health benefits outweigh the risk
What are the potential risks of adding chlorine to drinking water?
Chlorine is toxic
Damages the respiratory system in large enough quantities
Forms carcinogens with hydrocarbons
What is the equation used when reacting chlorine with water?
Cl2 + H2O —> HClO + HCl
What is the type of reaction between chlorine and water?
Disproportionation reaction
Chlorine is both oxidised and reduced
Give the equation when chlorine reacts with water in the presence of sunlight
2 Cl2 + 4 H2O —> 4 HCl + O2
What is desalination?
Converts saltwater into clean, potable water
By reverse osmosis
What are the advantages and disadvantages of desalination?
+ drinkable water produced in places where it isn’t readily available
- uses lots of energy
- can disturb marine ecosystems
