Question

What is the electronic configuration of an element with atomic number 13?

Answer 1

Hint: Electronic configuration of elements represent the distribution of electrons in different orbitals of atoms. A standard notation is followed to write electronic configuration in which all electron-containing atomic subshells, with the number of electrons they hold written in superscript, are placed in a sequence.

Complete answer:
The electron configuration of an element shows the number of electrons present in each atomic orbital in its ground state. The electrons are filled by using the Aufbau principle. It says that electrons will occupy the orbitals having lower energies before occupying higher energy orbitals. The order in which electrons are filled is illustrated in the diagram below. Read along the diagonal lines in the direction of the arrow.
The aluminium has atomic number 13. Thus, it contains 13 electrons in its atom. According to the Aufbau principle, 12 electrons will completely fill the 1s, 2s, 2p and 3s orbitals. The thirteenth electron is added to a 3p orbital, the sublevel next higher in energy. Then electron configuration of aluminium can be written as:
\[\text{1}{{\text{s}}^{\text{2}}}\text{2}{{\text{s}}^{\text{2}}}\text{2}{{\text{p}}^{\text{6}}}\text{3}{{\text{s}}^{\text{2}}}\text{3}{{\text{p}}^{\text{1}}}\]
Hence, the electronic configuration of an element with atomic number 13 is:
\[\text{1}{{\text{s}}^{\text{2}}}\text{2}{{\text{s}}^{\text{2}}}\text{2}{{\text{p}}^{\text{6}}}\text{3}{{\text{s}}^{\text{2}}}\text{3}{{\text{p}}^{\text{1}}}\]

Note:
There are many exceptions to the Aufbau principle such as the copper. The electronic configuration of copper is $\left[ \text{Ar} \right]\text{3}{{\text{d}}^{10}}\text{4}{{\text{s}}^{1}}$. This configuration disobeys the Aufbau principle due to two reasons:
1 – The relatively small energy gap between the 3d and the 4s orbitals.
2 – The completely filled d-orbital offers more stability than the partially filled configuration.