Now we can understand why the Periodic Table has the arrangement it has-the arrangement puts elements whose atoms have the same number of valence electrons in the same group. It is important to remember that the Periodic Table was developed on the basis of the chemical behavior of the elements, well before any idea of their atomic structure was available. It is the loss, gain, or sharing of valence electrons that defines how elements react. The similarity in chemical properties among elements of the same group occurs because they have the same number of valence electrons. fluorine and chlorine) each have seven valence electrons. beryllium and magnesium) each have two, and the halogens (e.g. lithium and sodium) each have only one valence electron, the alkaline earth metals (e.g. Valence electrons are also the determining factor in some physical properties of the elements.Įlements in any one group (or column) have the same number of valence electrons the alkali metals (e.g. The valence electrons (outer electrons) have the highest energy of the electrons in an atom and are more easily lost or shared than the core electrons. Because they are in the outer shells of an atom, valence electrons play the most important role in chemical reactions. | Key Concepts and Summary | Glossary | End of Section Exercises | Electron Configurations and Chemical ReactivityĪs described earlier, the Periodic Table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. | Electron Configurations and Chemical Reactivity | Variation in Atomic Radius | Variation in Ionization Energies | Variation in Electron Affinities | Correlate the effective nuclear charge with selected trends in periodic properties.
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