Page 254 - Instant notes

G6
MANY-ELECTRON ATOMS

Key Notes
An electron possesses ½ unit intrinsic spin angular momentum.
The two spin states, representing clockwise or anticlockwise
angular momentum, have quantum numbers, m s =+½ and −½.
Two electrons are termed paired if they have opposite spin.
In the orbital approximation, the wavefunction of a many-
electron atom is approximated as the product of the
wavefunctions of individual hydrogenic atomic orbitals,
ψ=ψ(1)ψ(2)….
Electrons in orbitals between the nucleus and the electron under
consideration repel the electron under consideration and reduce
the net attraction it experiences from the nucleus. The effect is
called shielding and is accounted for by reducing the actual
nuclear charge Ze to an effective nuclear charge Z eff e. Electrons in
s, p, d, f orbitals are successively better shielded by core electrons
(and consequently have higher energy) because the radial
probability functions of these orbitals successively penetrate less
towards the center of the atom.
No more than two electrons can occupy a given atomic (or
molecular) orbital, and when two electrons do occupy one orbital
their spins must be paired.

The electron configuration is the distribution of electrons into
individual atomic orbitals. The electron distribution of lowest
energy is called the ground state configuration.

The Aufbau (building-up) principle is the process of filling
atomic orbitals (sub-shells) with electrons in the order of
increasing sub-shell energy. Each individual atomic orbital (with
a unique set of n, l, m l quantum numbers) can accommodate a
maximum of two electrons with paired spins.
Electrons singly occupy degenerate orbitals of a sub-shell before
pairing into the same orbital, in the ground state configuration.
The ground electron state configuration contains the maximum
number of unpaired electrons.
The atomic term symbol is a short-hand notation that represents
an electron configuration of an atom. For a total spin angular