![]() ![]() Because it gets easier to form the ions, the reactions will happen more quickly. 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.This is the energy needed to break the bonds holding the atoms together in the metallic lattice. 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 alkali metals (group 1) have ns1 valence electron configurations and form M + ions, while the alkaline earth metals (group 2) have ns2 valence electron configurations and form M 2+ ions. The activation energy for a reaction is the minimum amount of energy which is needed in order for the reaction to take place. The chemical families consist of elements that have the same valence electron configuration and tend to have similar chemistry. 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. 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. However, only the magnesium reaction actually happens. Understanding Reactivity Trends Alkali Metals and Alkaline Earth Metals. Notice that both possible reactions are strongly exothermic, giving out almost identical amounts of heat. \ \ \ \Delta H = -360\ kJ/mol \nonumber \] In sub-groups, non-metals, alkali metals, alkaline earth metals, halogens & noble gases show the trends that the ionic size in period moving top to bottom.
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