The electronic configuration of an atom describes the arrangement of its electrons in atomic orbitals, following principles such as the Aufbau principle, Pauli exclusion principle, and Hund's rule. Electrons fill orbitals starting from the lowest energy level to higher ones. For example:
- Hydrogen (atomic number 1) has the configuration 1s¹, meaning one electron in the 1s orbital.
- Neon (atomic number 10) has the configuration 1s² 2s² 2p⁶, filling the first and second shells completely
- Sodium (atomic number 11) has the configuration 1s² 2s² 2p⁶ 3s¹, with one electron in the 3s orbital beyond the neon core
For the first 20 elements, a simplified shell model is often used where:
- The first shell can hold 2 electrons,
- The second shell can hold 8 electrons,
- The third shell can hold 8 electrons (though it can hold more in reality, but this simplified model is common for early elements)
For example, magnesium (atomic number 12) has 12 electrons arranged as 2 in the first shell, 8 in the second, and 2 in the third, written as 2,8,2
. In summary, the electronic configuration is written by listing the number of electrons in each orbital or shell, starting from the lowest energy level, and it explains the chemical properties and placement of elements in the periodic table
