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Group 7: Halogens

Atomic structure and the periodic table • The periodic table

Key concepts

What you'll likely be quizzed about

  • Halogen atoms each have seven electrons in their outermost shell and require one additional electron for a full shell configuration.
  • This electronic structure causes strong attraction for an extra electron, resulting in high electronegativity and oxidising ability.
  • As one moves down the group, atomic radius increases and increased electron shielding weakens this attraction, reducing reactivity.
  • Thus, the larger atomic size and shielding create a weaker attraction for an additional electron, explaining lower reactivity of bromine and iodine compared to chlorine.

Flashcards

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What happens when chlorine reacts with hydrogen?

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Chlorine and hydrogen form hydrogen chloride (HCl) by covalent bonding; HCl dissolves in water to yield hydrochloric acid.

Key notes

Important points to keep in mind

Halogen atoms possess seven outer electrons and form X⁻ ions or covalent bonds to complete their outer shell.

Reactivity decreases down Group 7 because greater atomic radius and shielding diminish nuclear attraction for incoming electrons.

Melting and boiling points increase down the group due to stronger London forces as molecular size and polarizability increase.

Halogen + metal produces ionic halides, often forming white crystalline solids; solubility is influenced by lattice energy and cation type.

Halogen + non-metal produces covalent compounds; hydrogen halides dissolve in water, forming acids.

A more reactive halogen displaces a less reactive halide from solution; the order is F₂ > Cl₂ > Br₂ > I₂.

Ionic/covalent character and physical properties vary with the metal or non-metal partner and oxidation conditions.

Predictive patterns include: larger atomic radius leads to lower electronegativity; heavier halogens form darker, less volatile substances.

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