ELECTRONIC STRUCTURE AND THE PERIODIC TABLE

Not chaos-like crush d and bruis d But, as the world, harmoniously confus d. Where order in variety we see. 

A rainbow, usually seen when the sun comes out after a rainfall, is the result of the dispersion of visible light (from the sun) into its component colors. The water t droplets act as prisms.  

In this chapter, we focus on electron arrangements in atoms, paying particular attention to the relative energies of different electrons (energy levels) and their spatial locations (orbitals). Specifically, we consider the nature of the energy levels and orbitals available to— 

With this background, we show how electron arrangements in multielectron atoms and the monatomic ions derived from them can be described in terms of— 

The electron configuration or orbital diagram of an atom of an element can be deduced from its position in the periodic table. Beyond that, position in the table can be used to predict (Section 6.8) the relative sizes of atoms and ions (atomic radius, ionic radius) and the relative tendencies of atoms to give up or acquire electrons (ionization energy, electronegativity). 

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Fireworks. The different colors are created by the atomic spectra of different elements. 

The noble gases, located at the end of each period, have electronic configurations of the type ns np, where n represents the number of the outermost shell. Also, n is the number of the period in the periodic table in which the element is found. 

The elements may be divided into types (Fig. 4-8), according to the position of the last electron added to those present in the preceding element. In the first type, the last electron added enters the valence shell. These elements are called the main group elements. In the second type, the last electron enters a d subshell in the next-to-last shell. These elements are the transition elements. The third type of elements has the last electron 

Inner transition groups Fig. 4-8. Periodic table as an aid to assigning electronic confignrations 

An effective way to determine the detailed electronic configuration of any element is to use the periodic table to determine which subshell to fill next. Each s subshell holds a maximum of 2 electrons each p subshell holds a maximum of 6 electrons each d subshell holds a maximum of 10 electrons and each / subshell holds a maximum of 14 electrons (Table 4-5). These numbers match the numbers of elements in a given period in the various blocks. To get the electronic configuration, start at hydrogen (atomic number = 1) and continue in order of atomic number, using the periodic table of Fig. 4-8. 

EXAMPLE 4.12. Using the periodic table, determine the detailed electronic configuration of magnesium. 

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The energy-ordering scheme (5-58) coupled with the Pauli or exclusion principle and Hund s rule leads us to a simple prescription for building up the electronic configurations of atoms. This aufbau principle is familiar to chemists and leads naturally to a correlation between electronic structure and the periodic table. The procedure is to place all the electrons of the atom into atomic orbitals, two to an orbital, starting at the... 

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