CHEMISTRYHALOGEBSLECTURES

CHEMISTRY LECTURE – HALOGENS

1. Introduction to Halogens

Halogens are elements found in Group 17 (Group VIIA) of the periodic table.

Element	Symbol	Atomic Number
Fluorine	F	9
Chlorine	Cl	17
Bromine	Br	35
Iodine	I	53
Astatine	At	85

2. Electronic Configuration of Halogens

Halogens have 7 electrons in their outermost shell.

Element	Electronic Configuration
Fluorine	2,7
Chlorine	2,8,7
Bromine	2,8,18,7
Iodine	2,8,18,18,7

Diagram of Outer Shell (Example: Chlorine)

The outermost shell contains 7 valence electrons.

3. Physical Properties of Halogens

• They exist as diatomic molecules (F₂, Cl₂, Br₂, I₂)
• Colored substances
• Low melting and boiling points (increase down the group)
• Non-metals
• Density increases down the group

Element	Color	State at Room Temp
Fluorine	Pale Yellow	Gas
Chlorine	Greenish Yellow	Gas
Bromine	Reddish Brown	Liquid
Iodine	Violet-Black	Solid

4. Chemical Properties of Halogens

(A) Reaction with Metals

Halogens react with metals to form salts (halides).

Example:

2Na + Cl₂ → 2NaCl

(B) Reaction with Hydrogen

They react with hydrogen to form hydrogen halides.

H₂ + Cl₂ → 2HCl

(C) Displacement Reaction

A more reactive halogen displaces a less reactive one.

Cl₂ + 2KBr → 2KCl + Br₂

Reactivity Order

F₂ > Cl₂ > Br₂ > I₂

5. Compounds of Halogens

(A) Hydrogen Halides

• HF (Hydrogen fluoride)
• HCl (Hydrochloric acid)
• HBr
• HI

(B) Metal Halides

NaCl, KBr, CaCl₂

(C) Bleaching Powder

CaOCl₂

(D) Silver Halides

AgCl, AgBr (used in photography)

6. Preparation of Chlorine (Laboratory Method)

Using Manganese (IV) oxide and Concentrated HCl

Equation:

MnO₂ + 4HCl → MnCl₂ + Cl₂ + 2H₂O

Apparatus Diagram

Chlorine gas is collected by downward delivery because it is denser than air.