Lecture on Group 7 and Group 0 Elements: Halogens and Noble Gases

Introduction

Elements in Group 7
- Fluorine: Poisonous yellow gas, very reactive
- Chlorine: Less reactive than fluorine, poisonous green gas
- Bromine: Reddish-brown volatile liquid, poisonous
- Iodine: Dark gray solid, can form poisonous purple vapors, used as an antiseptic
- Astatine and Tennessine: Not commonly discussed in the course
Diatomic Molecules
- Halogens exist as diatomic molecules: two atoms sharing electrons to form a covalent bond
- Example: Chlorine molecule
Covalent Bonds with Non-Metals
- Halogens form covalent bonds with non-metals (e.g., hydrogen, carbon)
- Compounds formed are simple molecular structures (e.g., hydrogen fluoride, carbon tetrachloride)
Trends in Group 7
- Melting and Boiling Points: Increase down the group
- Reactivity: Decreases down the group
  - Outer shell gets further from the nucleus, weakening the attractive force needed to gain an extra electron
  - Larger atoms (e.g., iodine) are less reactive
Ionic Bonds with Metals
- Halogens gain electrons to form 1- ions, called halides (e.g., fluoride, chloride)
- Commonly form ionic compounds with alkali metals (e.g., sodium chloride)
- Can form ionic bonds with other metals
Displacement Reactions
- More reactive halogens displace less reactive ones
- Example: Chlorine displaces bromine in potassium bromide to form potassium chloride
- Fluorine, chlorine, and bromine can all displace iodine

Characteristics
- Colorless gases with full outer shells, making them inert (non-reactive)
- Exist as single atoms
- Non-flammable
Boiling Point Trend
- Increases down the group

For further study, focus on displacement reactions and bonding properties of halogens