The halogens are good oxidising agents, and more reactive halogens can oxidise halide ions further down the group.Spectator ions don’t take part in the reaction – this is just an oxidation of the halide (Cl -, Br - or I -) ions by a halogen molecule (see the point just below). If this reaction happens in water (‘aqueous solution’), it’s more accurate to write this reaction ignoring the metal ions because they are just spectator ions. This reaction works as long as the ‘X 2’ halogen is higher up the group than the halogen in the ‘MY’ halide salt, where M is the metal and Y is the halide ion. This is known as a displacement reaction. A more reactive halogen can displace a less reactive halogen in a salt.These are vigorous, exothermic reactions. The metals react by losing electrons the halogens react by gaining them. The halogens react well with group 1 and 2 metals because these have electron configurations that complement the halogens.As one of the more reactive groups of elements, there are a variety of reactions the halogens take part in:.Iodine is the least electronegative (except astatine), so it is the least reactive. Electronegativity measures this how easily does an atom attract bonding electrons into its outer shell and hold onto them?įluorine is the most electronegative halogen, so it is the most reactive halogen. Electronegativity decreasing down the group is the reason why reactivity decreases down the group! Halogens react by ‘pulling in’ electrons to their outer shell to complete it.This is why fluorine (with only one inner shell shielding the nucleus) is the single most electronegative element in the periodic table, and electronegativity drops from there. The reason that electronegativity decreases down the group is because each halogen further down the group has an extra inner electron shell shielding the nucleus from the outer electron shell.Īs explained in Periodic Trends: Electronegativity more inner shells make it more difficult to attract electrons into (and keep them held in) the outer shell, which is increasingly further away from the nucleus.This is why fluorine and chlorine are gases at room temperature, bromine is a liquid and iodine a solid. The increasingly large halogen atoms with more electrons produce stronger van der Waals forces between the molecules, so more heat energy is needed to overcome them. F 2, Cl 2, Br 2) get stronger down the group. The reason that melting and boiling points increase down the group is because the intermolecular forces between the halogen molecules (e.g.As with group 1 and 2, the trends in properties and GENERAL reactivity in group 7 can be explained by their electronic configuration:.Iodine is the least reactive halogen (besides astatine which is often ignored because it is extremely rare). The halogens get less reactive – fluorine, top of the group, is the most reactive element known.The smallest halogen, fluorine, is the most electronegative element in the periodic table. Electronegativity decreases down the group.The color of the halogens gets darker – fluorine is pale yellow, followed by green chlorine, brown/purple bromine and purple iodine.The melting and boiling point gets higher – starting as gases, bromine is a liquid while iodine is a solid.As you go down the group, the properties of the elements change in the following ways:.
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