Group 7 Halogens – Properties, Reactions, Colours: O Level (5070) & IGCSE (0620) Ultimate A* Guide
Secure your A* in **Cambridge O Level Chemistry 5070** and **IGCSE Chemistry 0620** by mastering the **group 7 halogens** (F, Cl, Br, I). This guide provides **concise, exam-centered definitions** on their trends, **physical properties**, and essential **displacement reactions**.
A*-Grade Internal Study Hub (Maximize Your Links!):
Periodic Table Chapter (Pillars → Chapters) | Halogens Ultra Premium Notes (Syllabus → Notes) | Reactivity Module (Notes → Crash Course) | Formula Application in Crash Course (Formula sheet → Crash Course) | Past Paper Solved Halogen Notes (Past papers → Notes) | A-Grade Halogens Strategy (Tips pages → Crash Course)1. What are the Group 7 Halogens? (Exam-Centred Definition)
The **Group 7 elements** are known as the **Halogens** (Fluorine, Chlorine, Bromine, Iodine, and Astatine). They occupy **Group 17** in modern IUPAC numbering, but are traditionally and commonly referred to as **Group 7** in **CAIE O-Level Chemistry 5070** and **Cambridge IGCSE Chemistry 0620**.
Halogens (Definition for A* Grade)
The **Group 7 Halogens** are **non-metals** characterised by **seven valence electrons**. This electron configuration drives them to be highly **are group 7 halogens reactive** oxidizing agents that gain one electron to form a stable univalent anion (e.g., $Cl^-$). **What do group 7 halogens normally exist as**? They exist as diatomic molecules ($X_2$) to achieve stability.
Remember: **Why are group 7 called halogens**? The name translates to "salt-former," reflecting their tendency to react with metals to form salts (metal halides).
2. Physical Properties: States, Colours, and Trends
The **physical properties of group 7 halogens** show clear trends as you move down the group from Fluorine (F) to Iodine (I). These trends are essential for predicting properties and identifying halogens in the lab.
Key Property Trends (Top to Bottom)
- **Melting & Boiling Points:** **The boiling point of group 7 halogens** (and melting point) **increases** down the group. **What happens to the boiling point of group 7 halogens**? It increases because the size of the atoms increases, leading to stronger intermolecular forces (van der Waals forces) requiring more energy to break.
- **Density:** Increases down the group.
- **Physical State at RTP:** Changes from gas to liquid to solid.
Group 7 Halogens Colours and Physical State (MUST KNOW)
Know the state and **group 7 halogens colours** at room temperature (RTP) for your practical and theory papers:
- **Chlorine ($Cl_2$):** **Pale Green** Gas.
- **Bromine ($Br_2$):** **Reddish-Brown** Liquid (volatile, producing an orange-brown vapour).
- **Iodine ($I_2$):** **Shiny Purple-Black** Solid (sublimes easily to a purple/violet vapour).
3. Chemical Reactions: Reactivity and Displacement
The **chemical properties of group 7 halogens** are dominated by their tendency to gain an electron. This is measured by their **reactivity in group 7 halogens**.
Reactivity Trend (Key Concept)
The **reactivity of group 7 halogens** **decreases** as you move down the group.
Reason (Explain the reactivity of group 7 halogens): Down the group, the atoms have more electron shells, increasing the distance and shielding between the nucleus and the valence shell. This weakens the attractive force on an incoming electron, making it harder for the atom to gain an electron. Fluorine (F) is the most reactive, and Iodine (I) is the least reactive.
Displacement Reactions (The Redox Test)
**Group 7 halogens displacement reactions** demonstrate the reactivity trend. A more reactive halogen will **displace** a less reactive halogen from a solution of its metal halide salt.
- **Reaction with Metals:** **When group 7 halogens react with metals what happens**? They form ionic metal halides (salts). Example: $2Na(s) + Cl_2(g) \rightarrow 2NaCl(s)$.
- **Displacement Example (Chlorine displacing Bromine):** $$Cl_2(aq) + 2KBr(aq) \rightarrow 2KCl(aq) + Br_2(aq)$$ (Observation: Colourless solution turns orange/brown due to Bromine formation).
The element **which group 7 element will displace all other halogens** is Fluorine, due to its highest reactivity.
4. Exam Success Corner: Past Papers & Resources
O Level Chemistry 5070 Solved Paper (2023)
Detailed solutions covering Periodic Table and Group 7 theory questions.
IGCSE 0620 Solved Paper 6 (Practical)
See Group 7 anion (halide) identification in a practical context.
- Master the **physical properties of group 7 halogens** (state and colour).
- Understand the reason for the **trends in group 7 halogens** (size vs. nuclear attraction).
- Practice writing and balancing equations for **group 7 halogens displacement reactions**.
- Review the **Chemistry Cheat Sheet for Cations and Anions Test** to secure marks on Halide Ion tests (using $AgNO_3$).
A* Group 7 Revision Timeline (For Exam Success)
5. The Chemistry Guru: Prof. Faisal Janjowa's Crash Course
🧑🏫 Teacher Profile & Live Class Details
Prof. Faisal Janjowa, The Chemistry Guru, focuses on cutting-edge, **exam-centered definitions** and application techniques for **IGCSE Chemistry 0620** and **O Level Chemistry 5070**. His **Crash Course** distils the entire **O Level Chemistry 5070 syllabus** into the most useful, high-yield content.
Demo Video: Crash Course Overview
Essential Exam Tool: Halide Ion Identification Cheat Sheet
👉 **Live Class Details:** Next session is on **Qualitative Analysis (Ion Identification)**, a topic where Group 7 anions ($Cl^-$, $Br^-$, $I^-$) are crucial. Secure your spot via the Crash Course!
