Reactivity Trends - Group 7 Flashcards
(32 cards)
What are the colors and physical states of the halogens at room temperature?
Fluorine: Very pale yellow gas, highly reactive.
Chlorine: Greenish gas, reactive, poisonous in high concentrations.
Bromine: Red liquid, gives off dense brown/orange poisonous fumes.
Iodine: Shiny grey solid that sublimes to purple gas.
What trend is observed in melting and boiling points of halogens?
Increase down the group as molecules get larger, leading to stronger London forces, requiring more energy to break them.
Why do halogens exist as diatomic molecules?
To achieve a stable electronic configuration, each atom shares one electron, forming a covalent bond (X₂ molecules).
What is the general outer shell electron configuration of halogens?
s²p⁵, meaning they need one more electron to complete their outer shell.
How do halogens react in redox reactions?
They gain one electron to form X⁻ ions (halide ions), acting as oxidizing agents.
What is the trend in reactivity of halogens?
Reactivity decreases down the group because atoms get bigger, shielding increases, and nuclear attraction weakens, making it harder to gain an electron.
What is fluorine and why is it so reactive?
Fluorine (F2) is a pale yellow gas that reacts with nearly every substance. It is the most reactive halogen due to:
Small atomic radius
Very high electronegativity
Strong oxidising ability
What is astatine and why is it rare?
Astatine (At2) is a radioactive element that decays quickly, making it extremely rare. It is predicted to be the least reactive halogen.
What is a displacement reaction in halogens?
A more reactive halogen will displace a less reactive halogen from its compound.
What are the key observations in halogen displacement reactions?
Chlorine displaces bromide and iodide, bromine displaces iodide, but iodine cannot displace anything.
What are the color changes observed in displacement reactions?
Chlorine: Pale green (often colorless).
Bromine: Yellow.
Iodine: Brown (sometimes black solid present).
What are the displacement reaction equations for chlorine?
Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂ (yellow solution).
Cl₂ + 2I⁻ → 2Cl⁻ + I₂ (brown solution).
What are the displacement reaction equations for bromine?
Br₂ + 2I⁻ → 2Br⁻ + I₂ (brown solution).
How do halogens appear when an organic solvent is added?
Chlorine: Colorless. Bromine: Yellow. Iodine: Purple.
What is a disproportionation reaction?
A reaction where the same element is simultaneously oxidized and reduced.
What happens when chlorine reacts with water?
Cl₂ + H₂O → HClO + HCl (Chlorine is both oxidized and reduced).
What is the color change when universal indicator is added to chlorine water?
Red first (due to acidity), then colorless (due to bleaching by HClO).
Why is chlorine used in water treatment?
It kills bacteria, outweighing risks of toxicity and chlorinated hydrocarbon formation.
What are the risks of chlorine use?
Toxic gas (respiratory irritant, fatal in high doses)
Forms chlorinated hydrocarbons, possibly carcinogenic
What happens when chlorine reacts with cold NaOH?
Cl₂ + 2NaOH → NaCl + NaClO + H₂O. NaClO (sodium chlorate(I)) is used as bleach.
What happens when chlorine reacts with hot NaOH?
3Cl₂ + 6NaOH → NaClO₃ + 5NaCl + 3H₂O (Forms sodium chlorate(V)).
How do we test for halide ions?
Add nitric acid (HNO₃) to remove carbonates, then add silver nitrate (AgNO₃).
Why is nitric acid added before silver nitrate?
To remove carbonate impurities, which would form an unwanted Ag₂CO₃ precipitate.
What precipitates are formed in the silver nitrate test?
Chlorides (AgCl): White ppt.
Bromides (AgBr): Cream ppt.
Iodides (AgI): Pale yellow ppt.
