Group 7 (The Halogens) – Revision Flashcards

These flashcards cover all major facts, trends, reactions, tests, and applications associated with Group 7 halogens, helping you review both conceptual explanations and key observations for exams.

Which elements make up Group 7 (the halogens)?

Fluorine (F₂), Chlorine (Cl₂), Bromine (Br₂), Iodine (I₂), and Astatine (At₂).

What is the general outer-electron configuration of a halogen?

ns² np⁵ – giving 7 electrons in the outer shell.

Why do halogens exist as X₂ molecules rather than single atoms?

Each atom shares one electron to complete an octet, forming diatomic molecules (e.g., Cl₂).

State the physical state and colour of fluorine at room temperature.

Fluorine is a pale-yellow gas.

State the physical state and colour of chlorine at room temperature.

Chlorine is a greenish-yellow gas.

State the physical state and colour of bromine at room temperature.

Bromine is a red-brown liquid.

State the physical state and colour of iodine at room temperature.

Iodine is a grey solid that sublimes to a purple vapour.

What is the trend in boiling point down Group 7?

Boiling point increases down the group.

Explain why halogen boiling points increase down the group.

Larger molecules have more electrons, leading to stronger London dispersion forces that require more energy to overcome.

How does electronegativity change down Group 7, and why?

Electronegativity decreases because atomic radius and shielding increase, weakening nuclear attraction for bonding electrons.

Describe the trend in reactivity of halogens down Group 7.

Reactivity decreases down the group.

Give the reason halogen reactivity decreases down the group.

Larger, more shielded atoms attract an extra electron less strongly, making reduction harder.

What type of reaction occurs when a more-reactive halogen meets a less-reactive halide ion?

A displacement (redox) reaction in which the halogen oxidises the halide ion.

Write the ionic equation for chlorine displacing bromide ions.

Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂.

What colour change is seen when Cl₂ is added to KBr solution?

Solution changes from colourless to orange (Br₂ formed).

What colour change is seen when Br₂ is added to KI solution?

Solution changes from colourless to brown (I₂ formed).

Why is cyclohexane added when identifying halogens in solution?

Halogens dissolve in cyclohexane, producing brighter, distinguishable colours (e.g., Br₂ orange, I₂ purple).

How does oxidising power vary among Cl₂, Br₂, and I₂?

Oxidising power decreases: Cl₂ > Br₂ > I₂.

How does reducing ability vary among F⁻, Cl⁻, Br⁻, and I⁻?

Reducing power increases: F⁻ < Cl⁻ < Br⁻ < I⁻.

What observation is made when chloride ions react with concentrated H₂SO₄?

Misty white fumes of HCl (acid–base only, no redox).

List two observations when bromide ions react with concentrated H₂SO₄.

Brown fumes of Br₂ and colourless SO₂ gas (redox occurs).

Give three observations when iodide ions react with concentrated H₂SO₄.

Purple I₂ vapour/black solid, rotten-egg smell of H₂S, and possible yellow solid sulfur.

Outline the steps in the silver-nitrate test for halide ions.

1) Add dilute HNO₃ to remove CO₃²⁻; 2) add AgNO₃; 3) observe precipitate colour.

What precipitate colours form with AgNO₃ for Cl⁻, Br⁻, and I⁻?

Cl⁻: white AgCl; Br⁻: cream AgBr; I⁻: yellow AgI.

How are silver-halide precipitates distinguished using ammonia?

AgCl dissolves in dilute NH₃; AgBr dissolves only in conc. NH₃; AgI is insoluble in conc. NH₃.

Give the equation showing chlorine reacting with water to form disinfectant species.

Cl₂ + H₂O ⇌ HCl + HClO.

Write the equation for making household bleach from chlorine and cold NaOH.

Cl₂ + 2NaOH → NaCl + NaClO + H₂O.

State one benefit and one risk of using chlorine to treat drinking water.

Benefit: kills pathogenic microbes; Risk: toxic gas, can form carcinogenic chlorinated hydrocarbons.

Summarise five key trends down Group 7.

Boiling point ↑, electronegativity ↓, reactivity ↓, oxidising power ↓, halide reducing power ↑.

How does halogen solubility in water change down the group?

Solubility decreases from Cl₂ to I₂.