![]() The expected observations from adding halogen solutions to solutions of halide salts are summarised below The observations made during displacement reactions between solutions of halogens and halide ions can be used as evidence for the trend in reactivity down group 7. ![]() A displacement reaction is one in which a more reactive metal displaces a less reactive metal from its compound. One of the typical types of reactions which halogens are involved in are displacement reactions. For example, very low concentrations of chlorine compounds can be added to swimming pools to eliminate bacteria, and iodine can be used to sterilise wounds. ![]() Halogens are toxic and can be used to kill bacteria. Halogens are used as bleaching agents, for example chlorine is used to bleach wood to make white paper. Fluorine is a pale yellow gas and astatine is a dark black solid. Fluorine is above chlorine so would be paler in colour and astatine is below iodine so would be darker in colour. We can use this trend to predict the colours of fluorine and astatine. More energy is required to overcome the forces of attraction and the higher the melting and boiling points will be.Īs you descend group 7 the colour of the halogens becomes darker. The stronger the intermolecular forces of attraction between the halogen molecules, the harder it is to separate them. The larger the molecule, the stronger the intermolecular forces become. This means that the diatomic molecules made up of two of the atoms will also become larger. This trend occurs because the melting and boiling points are determined by the strength of intermolecular forces of attraction acting between the halogen molecules.Īs you descend the group, the atoms become larger. When a halogen is heated up, it is the diatomic molecules which are separated from each other. ![]() Astatine is below iodine so has the highest melting and boiling points and must be a solid at room temperature.Įach of the halogens exist naturally as a pair of atoms covalently bonded together as diatomic molecules. Fluorine is above chlorine so would have the lowest melting and boiling points and must be a gas at room temperature. You can use this trend to predict the state of fluorine and astatine at room temperature. This is evidenced by the change in state at room temperature as you descend the group. You must also know the trends in physical properties of the halogens, focusing on chlorine, bromine and iodine.Īs you descend the group, the melting points and boiling points increase.
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