What is the electronic configuration of Copper?

The electrons in an atom are organized into shells. Valence electrons are the number of electrons that make up an atom's outermost shell.
The atomic number of copper is 29.
2, 8, 18, 1 make up its electronic configuration.
The s, p, d, and f shells can also be used to express this setup.
 

It will be as follows: 1s²2s²2p⁶3s²3p⁶3d¹⁰4s¹4p⁰
 

Since d⁹ electronic configuration is less stable comparing to the d¹⁰ fully filled electronic configuration. Copper has an electronic configuration of 1s²2s²2p⁶3s²3p⁶3d¹⁰4s¹4p⁰.