CIE iGCSE Co-ordinated Sciences-C8.3 Group VII properties- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-C8.3 Group VII properties – Study Notes
CIE iGCSE Co-ordinated Sciences-C8.3 Group VII properties – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
- Describe the Group VII halogens, chlorine, bromine and iodine, as diatomic non-metals with general trends down the group, limited to:
(a) increasing density
(b) decreasing reactivity - State the appearance of the halogens at room temperature and pressure, r.t.p., as:
(a) chlorine, a pale yellow-green gas
(b) bromine, a red-brown liquid
(c) iodine, a grey-black solid
Supplement
- Describe and explain the displacement reactions of halogens with other halide ions
- Predict the properties of other elements in Group VII, given information about the elements
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Group VII Halogens: Chlorine, Bromine, and Iodine
Group VII elements, also called halogens, are non-metals found in the seventeenth group of the Periodic Table. They exist as diatomic molecules (X2) in their elemental form and have seven valence electrons, which makes them highly reactive non-metals.
General Properties:
- Exist as diatomic molecules: \( \text{Cl}_2 \), \( \text{Br}_2 \), \( \text{I}_2 \).
- Non-metals that are brittle in solid form and poor conductors of heat and electricity.
- Form salts when reacting with metals (halides) and hydrogen halides when reacting with hydrogen.
Trends Down the Group:
- Density: Increases down the group. Chlorine is a gas, bromine is a liquid, and iodine is a solid at r.t.p., reflecting increasing density with increasing relative atomic mass.
- Reactivity: Decreases down the group. Chlorine is the most reactive, bromine less reactive, and iodine is the least reactive. This is because the attraction of the nucleus for an additional electron decreases as atomic size increases, making it harder for the halogen to gain an electron.
Example
Compare the reactivity of chlorine and iodine.
▶️Answer/Explanation
Chlorine is more reactive than iodine because it is smaller in size, so its nucleus has a stronger attraction for an extra electron. Iodine is larger, so the nucleus attracts electrons less strongly, making it less reactive.
Example
Explain the trend in density of chlorine, bromine, and iodine.
▶️Answer/Explanation
Density increases down the group because the relative atomic mass of the halogens increases. Chlorine is a pale yellow-green gas, bromine is a red-brown liquid, and iodine is a grey-black solid at r.t.p., showing the increase in density from top to bottom.
Appearance of Halogens at Room Temperature and Pressure (r.t.p.)
Halogens exist in different physical states at room temperature and pressure, reflecting the trend in density down the group:
- Chlorine (\( \text{Cl}_2 \)): Pale yellow-green gas
- Bromine (\( \text{Br}_2 \)): Red-brown liquid
- Iodine (\( \text{I}_2 \)): Grey-black solid
Example
State the appearance of bromine at r.t.p.
▶️Answer/Explanation
Bromine is a red-brown liquid at room temperature and pressure.
Example
What is the physical state and colour of iodine at r.t.p.?
▶️Answer/Explanation
Iodine is a grey-black solid at room temperature and pressure.
Displacement Reactions of Halogens with Other Halide Ions
Halogens can react with halide ions in solution through displacement reactions. A more reactive halogen can displace a less reactive halogen from its salt solution. This occurs because more reactive halogens gain electrons more easily than less reactive ones.
General Rule: Reactivity of halogens decreases down the group: chlorine > bromine > iodine.
Examples of Displacement Reactions:
- Chlorine reacts with potassium bromide solution: \( \text{Cl}_2 + 2\text{KBr} \rightarrow 2\text{KCl} + \text{Br}_2 \) (bromine displaced, solution turns orange)
- Chlorine reacts with potassium iodide solution: \( \text{Cl}_2 + 2\text{KI} \rightarrow 2\text{KCl} + \text{I}_2 \) (iodine displaced, solution turns brown)
- Bromine reacts with potassium iodide solution: \( \text{Br}_2 + 2\text{KI} \rightarrow 2\text{KBr} + \text{I}_2 \) (iodine displaced)
- Bromine does not displace chlorine from potassium chloride solution and iodine does not displace bromine or chlorine, showing decreasing reactivity down the group.
Example
Predict the product when chlorine gas is bubbled into a solution of potassium iodide.
▶️Answer/Explanation
Chlorine is more reactive than iodine, so it displaces iodine from potassium iodide:
\( \text{Cl}_2 + 2\text{KI} \rightarrow 2\text{KCl} + \text{I}_2 \)
The solution turns brown due to iodine.
Example
Explain why bromine cannot displace chlorine from potassium chloride solution.
▶️Answer/Explanation
Bromine is less reactive than chlorine. Since displacement requires the halogen to be more reactive than the halide in solution, bromine cannot displace chlorine from potassium chloride, so no reaction occurs.
Prediction of Properties of Other Group VII Halogens
Based on the trends observed in chlorine, bromine, and iodine, the properties of other halogens (e.g., astatine) can be predicted:
- Physical state: Heavier halogens are expected to be solids at room temperature due to increasing molecular mass.
- Density: Increases further down the group. Astatine is denser than iodine.
- Reactivity: Decreases down the group. Astatine is expected to be less reactive than iodine, following the trend of decreasing ability to gain an electron.
- Appearance: Likely dark in colour, similar to iodine but darker due to higher atomic mass.
Example
Predict the reactivity of astatine compared to iodine.
▶️Answer/Explanation
Astatine is below iodine in Group VII, so it is larger and its nucleus has less attraction for an extra electron. Therefore, astatine is less reactive than iodine.
Example
Predict the physical state of astatine at room temperature.
▶️Answer/Explanation
Following the trend down Group VII, heavier halogens are solids. Therefore, astatine is predicted to be a solid at room temperature and pressure.