Type: Process Essays
Sample donated: Donald Turner
Last updated: September 22, 2019
Solid halides such as fluoride and chloride are hard to oxidise, and concentratedsulphuric acid isn’t strong enough of a reducing agent to pull the electronsaway from the ions.
The atomic radius of the first and second group 7 halides issmall; with a low amount of electromagnetic shielding meaning that the positiveattraction of the nucleus isn’t blocked by the layers of electrons. The smallnumber of electrons compared to the rest of group 7 means that there isn’t alarge amount of electron repel, resulting in there ions being small andcompact. Due to how close the outer electrons are to the nucleus along with theincreased pull, it’s hard to pull the outer electrons away from these ions. Asa result, you end up with either hydrogen fluoride or hydrogen chloride, due tothe hydrogen atom being attracted to the strong nuclear pull of the two halideions and creating a hydrogen halide. A bromide ion has a larger atomic radius,with more electromagnetic shielding and a greater amount of electrons. This resultsin the pull of the outer electrons being weaker than that of fluoride andchloride and therefore making bromide a stronger reducing agent.
Bromide is astrong enough reducing agent to be able to reduce the concentrated sulphuricacid, and giving the concentrated sulphuric acid enough electrons to turn intosulphur dioxide. It also ends up oxidising itself because it loses electronsand changes into bromine. Iodide ions are an even stronger reducing agent.
Theyhave a large atomic radius and their number of electrons also increases, alongwith the electromagnetic shielding, meaning the nucleus’ attraction to theouter electrons is even weaker than bromide. Because of how strong a reducingagent iodide it, it not only reduces the concentrated sulphuric acid to sulphurdioxide, the same process as the bromide, but goes on to further reduce the nowsulphur dioxide to just sulphur, completely splitting it from the oxygenmolecules by filling up sulphurs outer shell with electrons.