Give reasons: 1) atoms wid half filled or completed filled orbitals r xtra stable. 2) the energy of an electron is -ve. 3)Be and Mg do not show photoelectric effect.

Asked by prernamehta | 2nd Oct, 2010, 02:57: PM

Expert Answer:

Dear student

The filled and half-filled orbitals have extra stability due to the following reasons.

  1. Symmetrical distribution of electrons
    It is well-known that symmetry leads to stability. Thus if the addition or removal of an electron results in symmetrical distribution of the electrons in the orbitals, the electronic configuration becomes more stable. In such case there will be half-filled or completely filled orbitals. Electrons in the same subshell (here 3d) have equal energy but different spatial distribution. Consequently, their shielding of one another is relatively small and the electrons are strongly attracted by the nucleus.
  2. Exchange Energy
    The stabilizing effect arises whenever two or more electrons with the same spin are present in the degenerate orbitals of a subshell. These electrons tend to exchange their positions and the energy released due to this exchange is called exchange energy 
The number of exchanges that can take place is maximum when the subshell is either half-filled or completely filled (Fig).

Possible exchange for a d 5configuration

As a result the exchange energy is maximum and so is the stability

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Answered by  | 2nd Oct, 2010, 03:52: PM

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