Lecture Notes: Halogens and Noble Gases

Overview

In today's session, we explored the characteristics and trends of Group 7 elements (halogens) and Group 0 elements (noble gases).

Properties of Halogens:
- Fluorine: Poisonous yellow gas; extremely reactive.
- Chlorine: Poisonous green gas; less reactive than fluorine.
- Bromine: Red-brown volatile liquid; poisonous.
- Iodine: Dark grey solid; forms poisonous purple vapors; used as an antiseptic.
- Astatine & Tenocine: Not significant for the course content.
Diatomic Molecules:
- Halogens form diatomic molecules by sharing electrons and creating covalent bonds.
- Example: Chlorine (Cl<sub>2</sub>); similar bonding for other halogens.
Covalent Bonds with Non-Metals:
- Combine with hydrogen or carbon to form compounds like hydrogen fluoride or carbon tetrachloride.
- Known as simple molecular structures.
Trends in Group 7:
- Melting and Boiling Points: Increase down the group.
- Reactivity: Decreases as you go down the group.
- Larger atoms are less reactive due to increased distance from the nucleus.
Ionic Bonds with Metals:
- Halogens can gain an electron to form one-minus ions (halides): Fluoride, chloride, bromide, iodide.
- Common with Group 1 alkali metals (e.g., sodium chloride).
Displacement Reactions:
- More reactive halogen can displace a less reactive one.
- Example: Chlorine displacing bromine in potassium bromide to form potassium chloride.
- Fluorine, chlorine, and bromine can displace iodine due to higher reactivity.

Properties:
- Exist as colorless gases.
- Inert due to full outer electron shells (non-reactive, non-flammable).
- Exist as single atoms.
Trends in Group 0:
- Boiling points increase down the group (similar to halogens).

Key takeaway: Understand the properties, reactivity, and trends of halogens and noble gases.
Halogens are more reactive at the top of the group, while noble gases remain largely inert.

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