How are electrons
A designation of the most probable distribution is called
electron configuration. It refers to the distribution of
electrons in the different sublevels or orbitals as well as
in the main energy levels. There are 3 principles that you
have to consider.
1. As the electrons get farther from the
nucleus, their energy becomes greater.
2. The same principle holds true for the
sub-levels or orbitals. Therefore,
3. The maximum number of electrons per
orientation is 2. Therefore, only 2
electrons can occupy the s orbital, 6
electrons for p orbitals, 10 electrons for d
orbitals, and 14 electrons for f orbital.
that will help us
properly:1.Pauli’s Exclusion Principle
1. States that no two electrons in
an atom should have the same
four quantum numbers.
2. Electrons will go into available
orbitals singly before beginning to
3. Two electrons can only be in the
same orbital if they have opposite
When placing electrons into
the orbitals of polyelectronic
atoms, we use the Aufbau
AUFBAU (German: BUILD UP)
• Electrons will successively occupy the
available orbitals in order of increasing
• States that an electron tends to occupy the
level with a lower energy first.
• This principle states that in addition to
adding protons and neutrons to the
nucleus, one simply adds electrons to the
hydrogen-like atomic orbitals.
• States that the most stable
arrangement of electrons is that
which allows the maximum number of
• Applies to electrons that need to
occupy the same sub-level.
• This arrangement minimizes electron-
• Electrons occupy an orbital having
equal energy one by one first before
• Electrons go into hydrogen-like orbitals to
construct polyelectronic atoms.
• Elements in the same column have the same
number of valence electrons.
• Elements in the same column will have
similar chemical properties.
• Remember the “trick” for the order of the
energies of the orbitals.