![]() Because of their low ionization energies, they easily shed their outermost electrons, generating positive ions. Alkali metals such as potassium, sodium, and calcium are all highly reactive elements. Because it gets easier to form the ions, the reactions will happen more quickly. Understanding Reactivity Trends Alkali Metals and Alkaline Earth Metals. Notice that the ionization energies dominate this - particularly the second ionization energies. The graph shows the effect of these important energy-absorbing stages as you go down Group 2. These are necessary to convert the metal atoms into ions with a 2+ charge.Īfter this, there will be a number of steps which give out heat again - leading to the formation of the products, and overall exothermic reactions. the first + second ionization energies.Barium forms barium peroxide (BaO 2 ) because the larger O 2 2 ion is better able to separate the large Ba 2 + ions in the crystal lattice. All group 2 elements except barium react directly with oxygen to form the simple oxide MO. This is the energy needed to break the bonds holding the atoms together in the metallic lattice. The reactions of the alkaline earth metals with oxygen are less complex than those of the alkali metals. The formation of the ions from the original metal involves various stages all of which require the input of energy - contributing to the activation energy of the reaction. When Group 2 metals react to form oxides or hydroxides, metal ions are formed. It does not matter how exothermic the reaction would be once it got started - if there is a high activation energy barrier, the reaction will take place very slowly, if at all. The activation energy for a reaction is the minimum amount of energy which is needed in order for the reaction to take place. The reason for the increase in reactivity must again lie elsewhere. ![]() Similarly, calculating the enthalpy changes for the reactions between calcium, strontium or barium and cold water reveals that the amount of heat evolved in each case is almost exactly the same-about -430 kJ mol -1. The explanation for the different reactivities must lie somewhere else. However, only the magnesium reaction actually happens. Notice that both possible reactions are strongly exothermic, giving out almost identical amounts of heat. These elements are abundant in the earth and thus acquire this name. The elements occurring in group 2 of the periodic table are alkaline earth metals. \ \ \ \Delta H = -360\ kJ/mol \nonumber \] Reactivity of alkaline earth metals is such that they react with halogens to form halides, hydrogen to form hydrides, and acids to release dihydrogen.
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