What is shorthand notation?
Shorthand electron configuration of an element starts with the symbol of the noble gas in the previous period, followed by the rest of the electron configuration for the element in question.
In shorthand electron configuration, the electron configuration starts with the symbol of the noble gas in the previous period, followed by the additional configuration of the electrons for the given element.
For example, aluminum has the atomic number 13, which is the number of protons in the nuclei of its atoms. In a neutral atom, the numbers of protons and electrons are equal, so a neutral aluminum atom has 13 electrons. The electron configuration of aluminum can be written two ways.
Its full electron configuration is
Aluminum is in period 3, and the noble gas at the end of the previous period (period 2) is neon.
Its shorthand electron configuration is
Notice that the symbol of the noble gas is in brackets, followed by the configuration of the additional electrons in the element aluminum.
This works because the electron configuration of each element builds on the electron configuration of the noble gas from the previous period.