Noble Gas Notation
Another method of simplifying the electron distribution to the orbitals is called
the noble gas notation. In this method you represent all of the lower filled orbitals
up to the closest noble gas. By enclosing its symbol in brackets, it represents all
of the complete noble gas configuration. Then the remaining orbitals are written in
the usual way. An example of this can be shown by using the third period of
elements. By using neon as the noble gas, you write [Ne] to represent its orbital
structure, which is 1s^2 2 s^2 2 p^6. This allows you to write an element like sodium
as [Ne] 3s^1 , which is called sodium’s noble gas notation. The table in the next
section shows the noble gas notations of some of the transition elements in the
fourth period of elements. Notice that the base structure of argon is used and
represented as [Ar].
TRANSITION ELEMENTS
The elements involved with the filling of a d sublevel with electrons after two
electrons are in the s sublevel of the next principal energy level are often referred
to as the transition elements. The first examples of these are the elements
between calcium, atomic number 20, and gallium, atomic number 31. Their
electron configurations are the same in the 1s, 2s, 2p, 3s, and 3p sublevels. It is
the filling of the 3d and changes in the 4s sublevels that are of interest, as shown
in the following table.
Electron Configuration of Some Elements in the Fourth PeriodThe asterisk (*) shows where a 4s electron is promoted into the 3d sublevel.
This is because the 3d and 4s sublevels are very close in energy and that there is