Electron Configuration and Chemical Periodicity

Three atomic properties—atomic size, ionization energy (energy involved in removing an electron from an atom), and electron affinity (energy involved in adding an electron to an atom)—exhibit recurring trends throughout the periodic table. 

These atomic properties have a profound effect on many macroscopic properties, including metallic behavior, acid-base behavior of oxides, ionic behavior, and magnetic behavior of the elements and their compounds. 

The Electron-Spin Quantum Number The Exclusion Principle Electrostatic Effects and Energy-Level Splitting 

General Principles of Electron Configurations Unusual Configurations Transition and Inner Transition Elements 

Trends in Atomic Size Trends in Ionization Energy Trends in Electron Affinity 

3 The Quantum-Mechanical Model and the Periodic Table Bulding Up Periods 1 and 2 Buiding Up Period 3 Section Configurations Within Groups Building Up Period 4 

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Nevertheless, Bohr achieved two things with his theory. One was that he introduced the important idea that the differentiating electron should, in most cases, occupy an outer shell and not an inner one, as Thomson had thought was the case. Second, in spite of some arbitrary aspects, Bohr s scheme provided at least some correlation between electronic configurations and chemical periodicity. For example, the configuration of lithium is 2,1, while that of sodium, which lies in the same group chemically, is 8, 2,1. Similarly, beryllium and magnesium. 

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