Summary
Group 17 elements, also known as halogens, have distinct physical properties that change as you move down the group in the periodic table.
- Chlorine — a greenish-yellow gas at room temperature and pressure. Example: Chlorine is highly reactive and has a strong, unpleasant odour.
- Bromine — a reddish-brown liquid at room temperature and pressure. Example: Bromine is less reactive than chlorine but still has a strong odour.
- Iodine — a dark grey, crystalline solid at room temperature and pressure. Example: Iodine has a weak odour and is the least reactive of the three.
- Volatility — decreases down the group due to stronger van der Waals forces. Example: Iodine is the least volatile due to its larger electron cloud.
- Bond Strength — decreases down the group due to increased atomic size and electron-electron repulsion. Example: Fluorine and chlorine have stronger bonds than iodine.
Exam Tips
Key Definitions to Remember
- Volatility: The tendency of a substance to vaporize.
- Instantaneous dipole-induced dipole forces: Weak intermolecular forces arising from temporary dipoles.
Common Confusions
- Confusing volatility with reactivity.
- Misunderstanding the relationship between atomic size and bond strength.
Typical Exam Questions
- What is the trend in volatility down Group 17? Volatility decreases down the group.
- How does bond strength change in Group 17 elements? Bond strength decreases down the group.
- Why is iodine less volatile than chlorine? Iodine has stronger van der Waals forces due to larger electron clouds.
What Examiners Usually Test
- Understanding of trends in physical properties down the group.
- Ability to explain changes in volatility and bond strength in terms of molecular interactions.