Electronic Configuration

This resource is designed to support the teaching of electronic configuration - illustrating the application of the aufbau rule, Hund’s rule and the First in First out rule. This is the summary provided at the end:
Electrons repel one another but need to share the same space around the nucleus. Electrons are tiny compared with the size of the atom and they move at an enormously high speed (about 2,200 kilometers per second). Apart from Chromium and Copper, the atoms of the first 36 elements obey the aufbau rule and Hund’s rule. Energy levels 3 and 4 overlap and this means that electrons enter the 4s subshell before the 3d subshell. Chromium breaks the aufbau rule in order to half-fill its 3d subshell as this provides greater stability. Copper breaks the aufbau rule in order to fill its 3d subshell as this provides greater stability. When the transition metal atoms lose electrons to form cations the electrons come out of the 4s subshell first.