Group 7 - Halogens Flashcards
Which elements make up Group 7 of the periodic table?
The halogens in Group 7 are:
- Fluorine (F)
- Chlorine (Cl)
- Bromine (Br)
- Iodine (I)
- Astatine (At)
What is the molecular formula of halogens?
Halogens form diatomic molecules with the formula X₂ (e.g., F₂, Cl₂), where X represents the element.
What are the appearances of halogens at room temperature?
Fluorine (F₂): Pale yellow gas
Chlorine (Cl₂): Green gas
Bromine (Br₂): Red-brown liquid
Iodine (I₂): Grey solid
How do the boiling points of halogens change down Group 7?
The boiling points increase down Group 7 because:
- The molecules get larger and have a higher relative mass.
- This results in stronger induced dipole-dipole forces between molecules.
- more energy is required to overcome these forces
How does electronegativity change down Group 7?
it decreases because:
- Nuclear charge increases protons but:
- Atomic radius increases so outer electrons are further away from the nucleus
- Electron shielding increases reduces nuclear attraction
What do halogens act as?
oxidising agents as they gain an electron, causing another substance to lose an electron
How does the reactivity of halogens change down Group 7?
It decreases because:
- Atomic radius increases
- Outer electrons are farther from the nucleus and experience more shielding.g
- The electrostatic attraction between the outer electrons and the nucleus becomes weaker.
- It becomes harder for larger halogens to attract the electron needed to form a negative ion
How does the oxidising power of halogens change down Group 7?
Oxidising power decreases down Group 7 because:
- The halogens get larger and experience more shielding.
- This makes it harder for larger halogens to remove electrons
- Fluorine is the strongest oxidising agent, and iodine is the weakest.
What happens in halogen displacement reactions?
- A more reactive halogen displaces a less reactive halide ion from solution. - The displacing halogen is reduced to form the halide ion.
-The displaced halide is oxidised to form the halogen molecule.
What is the rule for halogen displacement reactions?
A halogen will displace any halide ion below it in Group 7
What are the displacement reactions for halogens and halides?
- Chlorine (Cl₂) displaces bromide (Br⁻) and iodide (I⁻)
- Bromine (Br₂) displaces iodide (I⁻):
- Iodine (I₂) does not displace any halides, so no reaction
What colour changes occur during halogen displacement reactions?
- Bromine displaces bromide, turning the solution yellow.
- Iodine displaces iodide, turning the solution orange/brown.
If no reaction occurs, the solution remains colourless.
What are halide ions?
negatively charged forms of halogens with a 1- charge
How do halide ions react in redox reactions?
They lose electrons to form neutral halogen molecules in oxidation reactions
What happens to the oxidation number of halide ions during oxidation?
It increases from -1 to 0, meaning the halide ion is oxidised
Why do halide ions act as reducing agents?
They donate electrons to another substance, causing its reduction
How does the reducing power of halide ions change down Group 7?
it increases because:
- Ionic radius increases
- More electron shielding weakens nuclear attraction
- Weaker electrostatic attraction makes it easier to lose electrons
Why is fluoride the weakest reducing agent?
- Smallest ionic radius
- Less shielding, making electron loss harder.
Why is iodide the strongest reducing agent?
- Largest ionic radius
- More shielding
What happens when halide ions react with concentrated sulfuric acid?
- Initially, hydrogen halide gases are formed
- Further reactions depend on the reducing power of the halide ion
How do fluoride and chloride react with sulfuric acid?
- Only acid-base reactions occur—no redox.
- HF (g) or HCl (g) gas is formed.
Observations and equations of fluoride and chloride with sulfuric acid
Misty white fumes of HF or HCl gas.
- NaF (s) + H₂SO₄ (aq) → NaHSO₄ (aq) + HF (g)
- NaCl (s) + H₂SO₄ (aq) → NaHSO₄ (aq) + HCl (g)
Why Do Fluoride and Chloride Not Undergo Redox?
Their reducing power is too weak to reduce sulfuric acid
How does bromide react with sulfuric acid?
- initial reaction: forms HBr gas
- Further reaction: Bromide reduces H₂SO₄ to SO₂, forming Br₂ vapour.
observations of bromide and sulfuric acid
- Misty white fumes of HBr gas.
- Orange bromine vapour.
- Choking SO₂ gas.
How does iodide react with sulfuric acid?
- Initial reaction: Forms HI gas (acid-base reaction).
- Further reactions: Iodide reduces sulfur all the way from +6 to -2, forming SO₂, solid sulfur (S), and H₂S gas.
observations and equations of iodide with sulfuric acid
- NaI (s) + H₂SO₄ (aq) → NaHSO₄ (aq) + HI (g)
- 2HI (g) + H₂SO₄ (aq) → I₂ (g) + SO₂ (g) + 2H₂O (l)
- 6HI (g) + SO₂ (g) → H₂S (g) + 3I₂ (s) + 2H₂O (l)
- Misty white fumes of HI gas.
- Violet iodine vapour.
- Yellow solid sulfur.
- Rotten egg smell of H₂S gas
What is a disproportionation reaction?
A reaction where the same element is both oxidized and reduced in the same reaction.
Give an example of a disproportionation reaction involving chlorine.
When chlorine reacts with water:
Cl₂(g) + H₂O(l) → HCl(aq) + HClO(aq)
Chlorine is oxidized from 0 to +1 in HClO and reduced from 0 to -1 in HCl.
How does chlorine disinfect water?
Chlorine reacts with water in a disproportionation reaction: Cl₂(g) + H₂O(l) → HCl(aq) + HClO(aq)
HClO dissociates into ClO⁻ ions, which kill bacteria: HClO → H⁺ + ClO⁻
What happens to chlorine in sunlight?
Chlorine reacts with water to form hydrochloric acid and oxygen: Cl₂(g) + 2H₂O(l) → 2HCl(aq) + ½O₂(g)
This removes the disinfectant (ClO⁻), so pools need regular chlorine addition.
What are the benefits of using chlorine in water treatment?
- Kills disease-causing microorganisms
- Prevents reinfection further down the water supply
- Removes bad tastes, smells, and discoloration
What are the risks of using chlorine in water treatment?
- Chlorine gas causes severe irritation if inhaled
- Reacts with organic compounds in water to form carcinogenic chlorinated hydrocarbons
What are some alternatives to chlorine for water disinfection?
- Ozone (O₃): Strong disinfectant but expensive and decays quickly
- Ultraviolet (UV) light: Damages microbial DNA but less effective in cloudy water
How is bleach made using chlorine?
Chlorine reacts with cold, dilute sodium hydroxide to form sodium chlorate(I):
Cl₂(g) + 2NaOH(aq) → NaClO(aq) + NaCl(aq) + H₂O(l)
Why is the bleach reaction a disproportionation reaction?
Chlorine is oxidized from 0 to +1 in NaClO and reduced from 0 to -1 in NaCl.
What is the active ingredient in household bleach?
Sodium chlorate (I), which contains chlorate(I) ions that act as oxidizing agents to kill bacteria.
How do you test for carbonate ions?
- Add dilute nitric acid (HNO₃) to the sample.
- If carbonate ions are present, effervescence occurs due to CO₂ gas
What is the equation for the carbonate test?
CO₃²⁻(aq) + 2H⁺(aq) → CO₂(g) + H₂O(l)
How do you confirm the presence of carbon dioxide gas?
Bubble the gas through limewater (Ca(OH)₂ solution). If CO₂ is present, limewater turns cloudy due to the formation of calcium carbonate
How do you test for sulfate (SO₄²⁻) ions?
- Add dilute nitric acid (HNO₃) to remove carbonate impurities
- Add a few drops of barium chloride or barium nitrate
- If sulfate ions are present, a white precipitate of barium sulfate forms.
What is the equation for the sulfate test?
Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)
How do you test for halide ions (Cl⁻, Br⁻, I⁻)?
- Add dilute nitric acid (HNO₃) to remove interfering ions.
- Add silver nitrate (AgNO₃) solution.
- Observe the precipitate color to identify the halide.
What are the precipitate colors for halide ions in the silver nitrate test?
- Chloride (Cl⁻): White precipitate (AgCl)
- Bromide (Br⁻): Cream precipitate (AgBr)
- Iodide (I⁻): Yellow precipitate (AgI)
What is the equation for the halide test with silver nitrate?
Ag⁺(aq) + X⁻(aq) → AgX(s)
(where X = Cl⁻, Br⁻, I⁻)
How do you confirm halide identity using ammonia (NH₃) solution?
- AgCl: Dissolves in dilute NH₃.
- AgBr: Insoluble in dilute NH₃ but dissolves in concentrated NH₃.
- AgI: Insoluble in both dilute and concentrated NH₃.
Why is it important to eliminate interfering ions? (CARBONATE)
- can give a false positive in the sulfate test because BaCO₃ is also a white precipitate.
- Add acid first to remove carbonates as CO₂
Why is it important to eliminate interfering ions (SULFATE)
- can interfere with the halide test because Ag₂SO₄ forms a white precipitate like AgCl.
- Solution: Add Ba²⁺ ions first to remove sulfates as BaSO₄.
What is the correct order for testing anions?
- Carbonates
- Sulfates
- Halides
