Chapter 10 - Group 7(17), The Halogens

Group 7 - The Halogens

The halogens: FluorineChlorineBromineIodine

Properties:-darker and denser going down the group(fluorine has atypical properties)size of atoms: -bigger going down the group (an extra shell on each one)electronegativity:the ability of an atom to attract electrons towards itself within a covalent bond-decreases down a group-shared electrons of H-X bond get further away from nucleus as atoms get larger, with increased shielding, so e.n. decsmelting and boiling points:-increase: -more electrons (stronger vdWs) ->more energy req to melt them and break the vdWs -lower the boiling point, more volatile the element

chemical reaction of halogens:oxidising ability-usually react by gaining an electron (to become -1)Halogens are oxidising agents and they become reduced.-increases up the groupdisplacement reactions the more reactive halides displace the less reactive onese.g. Cl2+2NaBr->Br2+2NaCl (chlorine is higher up and more reactive than bromine, so displaces it)this is a redox reaction bc chlorine oxidises bromine (removing 2 e-) and bromine reduces chlorine (adding 2e-)oxidationislossreductionisgain

reactions of halide ions:halide ions as reducing agents:-give away e- to become halogen molecules-larger the ion, the more easily it loses an e- (the e- that is lost from the outer shell is further away from the nucleus as the ion get larger, so less attraction)reactions with conc sulphuric acid:chlorine: 1. drops of sulphuric acid added2. no redox reaction bc chlorine is too weak of a reducing agenthowever, the reaction produces HCl, so is used for that reason ( same happens with fluorine but is a much more dangerous gas - an even weaker reducing agent)bromine:1) HBr produced as above2) BUT bromine is a strong enough reducing agent to reduce sulphuric acid to SO2.exothermic reactionsiodine:further reduces the sulphur, so SO", S and H2S are produced+6 -> -2 passing thru oxidation state 0, some solid yellow sulphur may be seen

uses of chlorineCl2+H2O <-> HClO+HClchlorine goes from 0 to -1 and 0 to +1, the whole reox reaction is happening to one atom, so it is a disproportionation reaction-used to purify water, killing bacteria thru oxidationother halogens act asimilarly, but are much more slowly going down the group