12.Group 7 (Halogens) & Group 0 (Noble Gases)

1. Group 7: The Halogens

The halogens are a group of reactive, poisonous non-metals:

• Fluorine: A poisonous yellow gas (highly reactive).

• Chlorine: A poisonous green gas.

• Bromine: A poisonous, volatile red-brown liquid.

• Iodine: A dark grey solid that forms poisonous purple vapors (also used as an antiseptic).

Key Features:

• Diatomic Molecules: Halogens exist as pairs of atoms (e.g., F2, Cl2) held together by a covalent bond (sharing electrons).

• Covalent Compounds: They can form covalent bonds with other non-metals (e.g., hydrogen fluoride, carbon tetrachloride).

• Ionic Bonds: When they react with metals, they gain one electron to form 1- ions, known as halides (fluoride, chloride, bromide, and iodide).

Trends Down Group 7:

• Reactivity Decreases: As you go down, the outer shell is further from the nucleus, weakening the attraction needed to pull in an extra electron.

• Melting/Boiling Points Increase: The atoms get larger, increasing the intermolecular forces.

Displacement Reactions:

• A more reactive halogen will displace a less reactive one from its compound.

• Example: Chlorine + Potassium Bromide → Potassium Chloride + Bromine. (Chlorine is higher in the group, so it takes the place of bromine).

2. Group 0: The Noble Gases

Noble gases include elements like Helium, Neon, and Argon.

• Inert: They are extremely unreactive because they already have full outer shells.

• Single Atoms: Unlike halogens, they exist as individual atoms (monatomic).

• Physical State: They are all colorless gases at room temperature.

• Non-flammable: They do not catch fire.

Trends Down Group 0:

• Boiling Points Increase: Similar to the halogens, boiling points increase as you move down the group because the atoms become larger.