Halogens are in group 7 of the periodic table: Fluorine, Chlorine, Bromine, Iodine, and Astatine.
As we descend the group, the atomic radius increases due to more electron shells, which corresponds to a decrease in reactivity amongst the halogens.
Fluorine is the most reactive, being a small atom with a strong ability to attract electrons, making it an effective oxidizing agent.
Astatine is the least reactive, being at the bottom of the group.
Boiling Points
Boiling points increase down the group due to larger atomic size and stronger London dispersion forces (Van der Waals forces).
Physical Appearance and States at Room Temperature
Fluorine: Yellow gas.
Chlorine: Green gas.
Bromine: Reddish-brown liquid (the only liquid non-metal in the periodic table).
Iodine: Solid with a gray appearance, dissolves in water to form a reddish-brown solution, and in organic solvents like hexane, it appears purple.
Astatine: Black solid.
Hydrogen Halides
The bond strength between hydrogen and the halogens weakens down the group, affecting the thermal stability and acidity of hydrogen halides (HF, HCl, HBr, HI).
HF has the highest boiling point due to hydrogen bonding, unlike other hydrogen halides.
Reactions with Aqueous Silver Nitrate
Used to test for halides: Chloride (white precipitate), Bromide (cream precipitate), and Iodide (yellow precipitate).
Ammoniacal silver nitrate can distinguish between these halides based on the solubility of their precipitates.
Reactions with Concentrated Sulfuric Acid
Chloride: Produces HCl gas with no further reaction.
Bromide: Reacts further to produce SO2, bromine, and possibly bromide fumes.
Iodide: Leads to a variety of products including sulfur dioxide, iodine, sulfur, and hydrogen sulfide (H2S), indicating strong reducing properties.
Disproportionation Reactions
Chlorine reacts with aqueous solutions (e.g., water, potassium hydroxide) to form compounds through disproportionation, changing oxidation states in the process.