Electron configurations aufbau process

Recall from Chapter 8 that ionization energy refers to the removal of an electron from an atom, or, in this case, from a molecule. We must count the valence electrons, choose the correct MO diagram, follow the aufbau process in placing the electrons, and then use the configurations to explain the ionization energy data. 

Here we will extend the rules used in writing electron configurations for the first ten elements to the rest of the elements. This process is based on the Aufbau principle. (The German word Aufbau means building up. ) The principle dictates that... 

This is just like the Aufbau process we used in Chapter 4 to develop the electron configurations of isolated atoms. There we put electrons into the atomic orbitals of isolated atoms here we put them into the molecular orbitals of a collection of atoms. 

It is important to realize that the orbital ordering (5-58) used in the aufbau process is not fixed, but depends on the atomic number Z. The ordering in (5-58) caimot be blindly followed in all cases. For instance, the ordering shows that 5s fills before 4d. It is tme that element 38, strontium, has a 4p 5s 4d° configuration. But a later element, palladium, number 46, has 4p 4d °5s° as its ground state configuration. The effect of adding more protons and electrons has been to depress the 4d level more than the 5s level. 

Use the aufbau process to predict ground-state electron configurations of atoms. 

To write electron configurations we will use the aufbau process. Aufbau is a German word that means "building up," and what we do is assign electron configurations to the elements in order of increasing atomic number. To proceed from one atom to the next, we add a proton and some neutrons to the nucleus and then describe the orbital into which the added electron goes. 

By considering the position of an atom in the periodic table, we can quickly determine the electron configuration, the number of valence electrons, the number of electrons in a particular subshell, or the number of unpaired electrons. Part (d) of this problem serves as a reminder that, for the lower d- and/-block elements, the actual electron configurations may be different from those predicted by using the aufbau process. 

The aufbau process is a method of writing electron configurations. Each element is described as differing from the preceding one in terms of the orbital to which the one additional electron is assigned. 

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