From Wikipedia,
the free encyclopedia.
In
physics and
chemistry, the inert pair
effect occurs when
electrons are pulled closer to
the
nucleus, making them stabler
and more difficult to ionise. This
is a
relativistic effect.
An electron around the nucleus
requires sufficient
kinetic energy in order not to
be pulled towards the nucleus.
This results in it having higher
speeds, with a higher force acting
on it by the nucleus. The effects
for the heavier elements are
appreciable, as electrons travel
closer to the speed of light,
c. The s-orbital
electrons are more affected in
this way since they have a greater
penetrating power.
The mass of the electron
depends on its speed, given by its
rest mass multiplied by the Lorenz
factor. Electrons in heavier
elements thus have greater
increases in their relativistic
masses.
The consequence of this is that
the
Bohr radius is decreased, as
seen by:
which can be obtained through
Planck's relationship,
Einstein's equation for
energy, and the concept that
electrons in a
Bohr atom would be a standing
wave in a stationary state.
As the electrons are pulled
closer to the nucleus by this
effect, they are stabilised and
harder to ionise. This is called
the inert pair effect. The
contraction of p-orbitals and
particularly d and f-orbitals is
somewhat less as the time spent
near the nucleus decreases as the
orbital
angular momentum increases.
The inert pair effect is
apparent from the chemistry of the
Group III and Group IV elements
and beyond. The lighter elements
in Group IV tend to have a valency
of +4, whereas the heavier
elements form 2+ ions that are
more stable than 4+ ions. For
instance, PbO is much more stable
than PbO2 which decomposes readily
to PbO.
