Halogens Study Guide

Halogens

• Halogens are group 7 elements.
• They are dangerous in their elemental forms.
• Fluorine: Poisonous yellow gas, highly reactive.
• Chlorine: Less reactive than fluorine; poisonous green gas.
• Bromine: Poisonous reddish-brown volatile liquid.
• Iodine: Dark gray solid forming poisonous purple vapors; antiseptic.
• Astatine and Tennessine: Not typically studied in detail.
• Halogens exist as diatomic molecules (two-atom molecules).
• They share electrons to form covalent bonds.
• Example: Chlorine (Cl₂).
• Outer shell arrangements are similar for all halogens.
• Halogens form covalent bonds with other non-metals (e.g., hydrogen, carbon).
• Creating simple molecular structures (e.g., HF, CCl₄).

Trends in Halogens

• Melting and boiling points increase as you move down the group.
• Reactivity decreases as you move down the group.
• This is because the outermost electron shell gets further from the nucleus, decreasing attraction for additional electrons.
• Larger atoms are less reactive.

Halide Ions

• A halogen that gains an electron becomes a halide ion with a 1- charge.
• Fluorine: Fluoride (F⁻)
• Chlorine: Chloride (Cl⁻)
• Bromine: Bromide (Br⁻)
• Iodine: Iodide (I⁻)
• Halides commonly form ionic compounds with alkali metals.
• Example: Sodium chloride (NaCl)

Displacement Reactions

• More reactive halogens displace less reactive halogens.
• Example: Chlorine displaces bromine from potassium bromide.
• Reaction: Cl₂ + KBr → KCl + Br₂
• Reactivity order: Fluorine > Chlorine > Bromine > Iodine.

Noble Gases

• Noble gases are group 0 elements.
• They are colorless gases.
• They have full outer electron shells.
• They are inert (don't react).
• They are monatomic (exist as single atoms).
• They are non-flammable.
• Boiling points increase going down the group.