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Group 7A Elements Section 20.7

Group 7A Elements Section 20.7. By: Hiromi Sarah Fukuzaki. background info. Also known as the “ Halogens ” Valence electron configuration s 2 p 5 . Consists of Fluorine, Chlorine, Bromine, Iodine and Astatine.

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Group 7A Elements Section 20.7

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  1. Group 7A ElementsSection 20.7 By: Hiromi Sarah Fukuzaki

  2. background info • Also known as the “Halogens” • Valence electron configuration s2p5. • Consists of Fluorine, Chlorine, Bromine, Iodine and Astatine. • High electronegativity values, tends to form covalent bonds with other nonmetals & ionic with metals (lower oxidation state; if higher, polar covalent bonds).

  3. More Background Info • Not considered free elements, instead they are found as halide ions due to their reactivity. Negligible due to its radioactivity(isotopes) and short life (half-life 8.3 hours)

  4. HYDROGEN HALIDES • Can be prepared through this kind of reaction: • H2(g) + X2(g)  2HX(g) • Violent reaction occurs when fluorine and hydrogen are mixed. • Hydrogen and chlorine can coexist in the dark, exposing these to ultra-violet light causes an explosively fast reaction. (hydrogen-chlorine cannon.) • Bromine and iodine react slower with hydrogen • Hydrogen Halides can also be created by treating a halide salts with acid. • CaF2(s) + H2SO4(aq)  CaSO4(s) + 2HF(g) • 2NaCl(s) + H2SO4(aq)  Na2SO4(s) + 2HCl(g) • Oxidizing agents cannot be used to create hydrogen halides. • Ex: sulfuric acid. Phosphoric can be used to form hydrogen halides

  5. Properties of hydrogen halides • High boiling point for hydrogen fluoride. (Hydrogen bonding) • When dissolved in water, hydrogen halides behave as acids. • Dissolve completely except for hydrogen fluoride. • Water is a stronger base for all except fluorine.

  6. Acid strength • Cannot be determined in water, but can in pure acetic acid. • H–I > H–Br > H–Cl > H–F Strongest acid --- weakest acid • Why is HF the only weak acid in group 7A? • Must look at the dissociation equilibrium equation • Acid strength depends on Ka • Small Ka = weak acid • K depends on △G∘ • △G∘ depends on △H∘ & △S∘ • To explain acid dissociation must know the factors determining △H∘ & △S∘. (mostly entropy since -△S∘ is unfavorable.)

  7. Hydrochloric acid • Most important of the hydrohalic acids (aqueous solutions of hydrogen halides). • Hydrofluoric acid used to cut glass • Done by reacting hydrofluoric acid with silica to form SiF4 • SiO2(s) + 4HF(aq)  SiF4(g) + 2H2O(l)

  8. Oxyacids • All halogens, except fluorine, combine with oxygen atoms to form a series of oxyacids. • Strength of the acids vary depending on the number of oxygens attached to the halogen.

  9. oxychloro anion structures

  10. Hypochlorous acid • Formed when chlorine gas is dissolved in cold water. Cl2(aq) + H2O(l) ⇌ HOCl(aq) + H+(aq) + Cl-(aq) • Reaction is called a disproportional reaction, due to the reduction and oxidation taking place.

  11. OF2

  12. Other halogen compounds • Halogens react with each other to form interhalogen compounds. • Abn n = 1,3,5 or 7 and A is the larger halogen. • Compound structures can be predicted by the VSEPR model. • Interhalogens are volatile, highly reactive that act as a strong oxidizing agent.

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