The tendency to attain either a half filled or fully filled set of d orbitals at the expense of the outer s orbital
is shown by both chromium and copper and should be noted. This apparent irregularity will be discussed in more
detail in Chapter 13.
Note. The electronic configuration of any element can easily be obtained from the periodic table by adding up
the numbers of electrons in the various quantum levels. We can express these in several ways, for example electronic
configuration of nickel can be written as Is22s22p63s63