8/30/2023 0 Comments Group 7 reactivity trend![]() It starts by producing yellow/green chlorine gas and then condensing this to a yellow/green liquid. This next short video shows chlorine, bromine and iodine. We can, however, predict what its properties might be by exploring the trends in the group. FĪstatine is very radioactive and short-lived. Group 7 is also known by its more modern name of Group 17. ![]() For a liquid like bromine or a solid like iodine, it also includes the energy that is needed to convert them into gases.This page introduces the Halogens in Group 7 of the Periodic Table. For a gas like chlorine, this is simply half of the bond enthalpy (because breaking a Cl-Cl bond produces 2 chlorine atoms, not 1).This is the energy needed to produce 1 mole of isolated gaseous atoms starting from an element in its standard state (gas for chlorine, and liquid for bromine, for example, both of the form X 2).The faulty explanation is incorrect even if restricted to chlorine, bromine and iodine: Although the ease with which an atom attracts an electron matters, it is not as important as the hydration enthalpy of the negative ion formed. Down the group, the ions become less attractive to water molecules as they get larger. Using the figures from the previous table:īoth of these effects contribute, but the more important factor-the one that changes the most-is the change in the hydration enthalpy. It is helpful to look at the changes in electron affinity and hydration enthalpy down the group. The decrease in atomization energy between these three elements is relatively small, and would tend to make the overall change more negative down the group. Why does oxidizing ability decrease from chlorine to bromine to iodine? The fifth column measures the energy released when 1 mole of gaseous ions dissolves in water to produce hydrated ions, as in the following equation, which is not equivalent to that above: The first electron affinity is defined as the energy released when 1 mole of gaseous atoms each acquire an electron to form 1 mole of gaseous 1- ions, as in the following equation: In symbol terms: Fluorine generates a large amount of heat when it forms its hydrated ion, chlorine a lesser amount, and so on down the group. The amount of heat evolved decreases quite dramatically from the top to the bottom of the group, with the biggest decrease between fluorine and chlorine. The table below shows the energy involved in each of these changes for atomization energy, electron affinity, and hydration enthalpy (hydration energy):Ĭonsider first the fifth column, which shows the overall heat evolved, the sum of the energies in the previous three columns. The isolated ions are surrounded by water molecules hydrated ions are formed (hydration).Each atom gains an electron (electron affinity this is the element of the process of interest in the faulty explanation.).The diatomic molecule must split into individual atoms (atomization).This may be a gas, liquid or solid at room temperature, depending on the halogen. The halogen starts as a diatomic molecule, X 2.The argument about atoms accepting electrons applies only to isolated atoms in the gas state picking up electrons to form isolated ions, also in the gas state. This problem stems from examining a single part of a very complicated process. However, fluorine's electron affinity is less than that of chlorine. ![]() Fluorine's tendency to form a hydrated ion is much higher than that of chlorine. The problem with this argument is that it does not include fluorine. Electron affinity is described in detail on another page. This is equivalent to saying electron affinity decreases down the group. The larger atoms are therefore less effective at attracting new electrons and forming ions. As the atoms get larger, the new electrons are further from the nucleus and increasingly shielded by the inner electrons (offsetting the effect of the greater nuclear charge). The ease of ionization depends on how strongly the new electrons are attracted. The following explanation is normally given for the trend in oxidizing ability of chlorine, bromine and iodine.
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