The electron configuration for a chlorine atom is: 1s2 2s2 2p6 3s2 3p5. What electron configuration represents the electrons that make up only the core electrons for a chlorine atom? A. 1s2 2s2 2p6 3s2 B. 1s2 2s2 2p6 3s2 3p5 C. 1s2 D. 1s2 2s2 2p6
The correct answer and explanation is:
The correct answer is A. 1s² 2s² 2p⁶ 3s².
To understand why, it is important to first define the difference between core electrons and valence electrons. Core electrons are those that are in the inner energy levels of the atom, typically occupying the orbitals closest to the nucleus. Valence electrons, on the other hand, are found in the outermost energy level (shell) and are involved in chemical reactions and bonding.
In the case of chlorine (Cl), the electron configuration is:
1s² 2s² 2p⁶ 3s² 3p⁵.
- The 1s² 2s² 2p⁶ portion represents the core electrons, as these are all in the first and second energy levels, which are considered inner orbitals.
- The 3s² 3p⁵ portion represents the valence electrons, as they are in the third energy level, which is the outermost shell for chlorine.
To find the core electron configuration for chlorine, we remove the outermost electrons (those in the third shell) and are left with the configuration for the inner shells: 1s² 2s² 2p⁶ 3s².
Thus, the electron configuration that represents only the core electrons of chlorine is 1s² 2s² 2p⁶ 3s², which corresponds to option A. These electrons are not involved in bonding but instead serve to stabilize the atom’s structure by filling the inner orbitals.