Free-radical halogenation distribution". For propane and higher alkanes, the hydrogen atoms which form part of CH (or CH) groups are preferentially replaced. The reactivity of the different halogens varies considerably. The relative rates are: fluorine (108) > chlorine (1) > bromine (7 × 10) > iodine (2 × 10). Hence, the reaction of alkanes with fluorine is difficult to control, that with chlorine is moderate to fast, that with bromine is slow and requires high levels of UV irradiation while the reaction with iodine is practically nonexistent and thermodynamically unfavorable. A common method in organic synthesis employing is the Wohl–Ziegler reaction, which
Chemistry: A Volatile History all the elements in their order: Notice carbon and silicon are in Group IV and the volatile gases fluorine, chlorine and bromine are in Group VII. Mendeleev was sufficiently confident in the layout of his table that he was willing to leave gaps for unknown elements to make the pattern fit – believing other elements would later be discovered that filled the gaps. So, for Mendeleev to be vindicated, the gaps needed to be filled, and luckily, in 1859, new instrumentation had been developed for discovering elements. Robert Bunsen knew that when certain elements burned in the flames of his