1. Filling Order:
* Follow the Aufbau principle and Hund's rule to fill the orbitals in order of increasing energy levels.
* The order is: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p...
2. Number of Electrons:
* The atomic number (42) tells us there are 42 electrons to distribute.
3. Electronic Configuration:
* 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹ 4d⁵
Explanation:
* The first three shells (1s, 2s, 2p, 3s, 3p) are filled completely.
* The 4s subshell is filled with 2 electrons.
* The 3d subshell is filled with 10 electrons.
* The 4p subshell is filled with 6 electrons.
* The 5s subshell has 1 electron.
* The 4d subshell has 5 electrons (this is a special case where the 4d subshell is half-filled, contributing to the stability of the atom).
Important Note: This is the ground state electronic configuration. In some cases, elements may have excited state configurations where electrons occupy higher energy levels.
