AS Chemistry
14/03/2024
Electronic Configuration
The Aufbau Principle and Hunds Rule (‘bus rule’) will be tested in principal as explained
below.
Electrons are filled up using the:
1s 2s etc notation
and/or
electron in a box notation
N.B: arrows represent the filling order for EACH subshell (Aufbau Principle)
Complete the following table using the 1s2s notation:
Atom/ion
No. of electrons
FULL electronic configuration
Oxygen
Chlorine
Magnesium ion
Oxide Ion
Nitride Ion
Neon
Carbon
Sodium
Hydrogen Ion
Some of Atoms and Ions have the SAME electronic configurations. SUGGEST a term used
to explain this? ………………………………………………………………………………………………………………….
3rd Principal Quantum Number i.e 3rd Shell
Electronic configuration of the elements that fill electrons in the 3rd shell, THREE principles
must be considered.
1) The Energy levels for the 4s and 3d subshells (when using the 1s 2s notation)
2) When writing the electronic configuration for IONS - AWLAYS remove the 4s
electrons FIRST (applies to the first row of the transition elements)
3) ‘Stable’ configurations when looking at Electron (when using the electron in the box
notation – ONLY exceptions tested in the exam are for Cr & Cu ATOMS, this is not in
accordance with the Aufbau principle)
Now complete the FULL electronic configurations of the following, using the 1s 2s
notation. DO NOT DO Chromium and Copper
Atom/ion
Scandium
Bromine
Copper
Copper ion
Bromide ion
Iron
Iron (II)
Iron (III)
Chromium
Chromium (III)
No. of electrons
FULL electronic configuration