Topic 11 - Halogens

They are all diatomic

Halogen - molecule (eg. Cl) Halide - ion (eg. Cl-)

• Gas • Pale yellow in pure form • Cannot exist in aqueous solutions • colourless in organic solutions

• gas • pale green in pure form • cannot exist in aqueous solution • pale green in organic solution • poisonous • fairly reactive • BP -34°C

• liquid • red-brown in pure form • yellow-orange in an aqueous solution • red in an organic solution • gives off an orange vapour at room temperature • BP = 59°C

• crystalline solid • dark grey in pure form • brown in aqueous solution • purple in organic solution • gives off a purple vapour when heated • BP = 185°C

• solid • black in pure form • there is not enough to dissolve it • MP = 300°C

They get less reactive as the group descends Because there is a greater distance between protons and the electrons it’s trying to gain in elements such as iodine and astatine compared to fluorine and chlorine- therefore the attraction is weaker and it’s harder to get the extra electron to fill the outer-shell

Colourless gas

They dissociate , therefore it can conduct electricity Does not dissociate in methylbenzene , therefore it cannot conduct