The Halogens-inorganic chemistry Flashcards
(16 cards)
How does electronegativity change down Group 7?
Decreases down the group.
Atomic radius increases → bonding pair is further from the nucleus.
More shielding from inner shells reduces nuclear attraction.
Fluorine is the most electronegative element.
How does boiling point change down Group 7?
Increases down the group.
Halogen molecules become larger → more electrons → stronger van der Waals forces.
More energy is required to overcome intermolecular forces.
Fluorine and chlorine are gases, bromine is a liquid, iodine is a solid at room temp.
How does oxidising ability change down Group 7?
Decreases down the group.
Halogens act as oxidising agents by gaining electrons.
Down the group: larger atomic radius + more shielding = less attraction for electrons.
✅ Chlorine displaces Br⁻ and I⁻, bromine displaces I⁻, iodine displaces none.
What happens in halogen displacement reactions?
A more reactive halogen displaces a less reactive halide ion from solution.
Example:
Cl2+2𝐵𝑟-→2𝐶𝑙−+𝐵r2
✅ Colour changes:
Br₂ = orange
I₂ = brown/purple in organic solvent
How does reducing ability change down the group?
Increases down the group.
Halide ions act as reducing agents by donating electrons.
I⁻ is the strongest reducing agent; F⁻ the weakest.
✅ Easier to lose electrons when the ion is larger and has more shielding.
How do halides react with concentrated sulfuric acid?
NaF and NaCl: only acid-base reaction → HF or HCl formed.
NaBr: acid-base + redox → Br₂, SO₂ formed (steamy fumes + brown vapour).
NaI: acid-base + multiple redox → I₂, SO₂, H₂S formed (black solid, bad smell).
✅ Reactivity increases down the group due to stronger reducing power.
What happens when AgNO₃ is added to halide solutions?
Ag⁺ + X⁻ → AgX (s)
Precipitate colours:
AgCl = white
AgBr = cream
AgI = yellow
✅ Test confirms presence of halide ions.
Why is nitric acid added before silver nitrate?
Removes interfering ions like carbonate or hydroxide.
Prevents false positives (e.g. white precipitate from Ag₂CO₃).
✅ Acidifying ensures accurate halide ion detection
How do silver halides behave with ammonia?
AgCl dissolves in dilute NH₃.
AgBr dissolves in concentrated NH₃.
AgI is insoluble in NH₃.
✅ This step helps distinguish between halides after the precipitate forms.
Why is ammonia added after AgNO₃ in the halide test?
Confirms identity of halide by differential solubility
Helps distinguish between AgCl, AgBr, AgI when colours are unclear.
What happens when chlorine reacts with water?
Cl 2+H2O→HCl+HClO
Chlorine is disproportionated:
One Cl atom is reduced to Cl⁻ in HCl
One Cl atom is oxidised to Cl⁺ in HClO (chlorate(I) ion)
✅ HClO is a weak acid and kills bacteria in water.
What is the reaction of chlorine with water in the presence of sunlight?
Cl2+H 2O→2HCl+ 1/2 O2
Chlorine is broken down more rapidly in sunlight
Less effective at killing bacteria
✅ Why swimming pools need frequent chlorine top-ups.
Why is chlorine added to drinking water despite being toxic?
Kills pathogens like bacteria and viruses
Prevents waterborne diseases (e.g. cholera, typhoid)
HClO (chlorate(I) acid) disinfects water
Health benefits outweigh the risks of chlorine’s toxicity.
What are the risks of using chlorine in water?
Toxic gas → respiratory irritant
Can form chlorinated hydrocarbons (carcinogens) when reacting with organic compounds in water
✅ Must balance public health vs. chemical safety when assessing use.
What happens when chlorine reacts with cold, dilute sodium hydroxide?
Cl2+2NaOH→NaCl+NaClO+H 2O
Chlorine is disproportionated again
Forms sodium chloride (NaCl) and sodium chlorate(I) (NaClO)
✅ Used in household bleach and disinfectants.
What is NaClO used for?
Active ingredient in bleach
Kills bacteria, cleans surfaces
Also used in water purification
