Their melting and boiling points are low and increases down the Group. In a nutshell, halogens are non-metals and exist as diatomic covalent molecules. Chlorine is the oxidising agent while iodide is the reducing agent. Hence, Cl 2 has been reduced and I – has been oxidised. Here, you can see that the oxidation state of chlorine decreases from 0 in Cl 2 to -1 in Cl –, while oxidation state of iodine increases from -1 in I – to 0 in I 2. If we convert this chemical equation to ionic equation, we realised that this is a redox reaction.Ĭancel away the spectator ions, we will have Cl 2 + 2I – → 2Cl – + I 2. A brown solution is formed due to the formation of iodine. Interesting observation can be made in this reaction – pale greenish yellow chlorine is bubbled into colourless solution of potassium iodide. Put it in chemistry terms, the more reactive chlorine displaces less reactive iodine from aqueous potassium iodide, forming potassium chloride and iodine. When chlorine is added to potassium iodide, the more reactive chlorine will take the place of iodine, forming potassium chloride, leaving iodine back as an element. A more reactive halogen can displace a less reactive halogen from its halide solution.įor example, we have potassium iodide. The interesting reaction halogens can undergo is displacement reaction. Chlorine is more reactive than bromine, and bromine is more reactive than iodine. Fluorine is the most reactive non-metal in the Periodic Table. The halogens become less reactive down the Group. The compounds that halogens formed with metals are all ionic. Ion of fluorine is fluoride, ion of chlorine is chloride, ion of bromine is bromide and that of iodine is iodide. One electron is taken in to achieve stable noble gas octet electronic configuration. Each halogen atom has seven electrons in the valence shell. Halogens form an ion with a charge of -1. A bright flame is observed in this reaction. For example, sodium burns in chlorine to form sodium chloride. Halogens are very reactive non-metals, they react with metals to form ionic salts. Chemical Properties Formation of ionic compound Fluorine is pale yellow, chlorine is pale yellow-green, bromine is reddish brown, while iodine is purplish black.Īll halogens are poisonous and must be handled carefully in the Chemistry lab. The colour intensity increases down the Group. Bromine exists as liquid, while iodine exists as solid.Īll the halogens are coloured. At room conditions, fluorine and chlorine exist as gases. Their boiling points increase down the Group. Hence, the melting point and boiling point of halogens are low. The forces between the molecules are weak, little amount of energy is required to overcome this weak intermolecular forces of attraction. Each molecule is made of two atoms covalently bonded together, hence we call them diatomic molecules. Halogens are non-metals that exist as molecules. The elements in this Group are fluorine, chlorine, bromine, iodine and astatine. Group VII elements are called the halogens.
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