Write electron configurations for the following atoms using the noble gas notation. (a) Ni chemPad Help [Ar]4s2 3d8 Correct. (b) Ga chemPad Help [Ar]4s2 3d10 4p1 Correct. (c) Cu
The correct answer and explanation is:
Sure! Here’s the electron configuration for Copper (Cu) using noble gas notation, followed by a detailed explanation:
(c) Copper (Cu) electron configuration:
Cu: [Ar] 4s¹ 3d¹⁰
Explanation (about 300 words):
Copper has an atomic number of 29, meaning it has 29 electrons. When writing electron configurations, we fill orbitals following the Aufbau principle, which suggests electrons fill the lowest energy orbitals first. For copper, the expected configuration by strict Aufbau order would be:
- [Ar] 4s² 3d⁹
This means after filling Argon’s electron configuration ([Ar] = 1s² 2s² 2p⁶ 3s² 3p⁶), the next electrons should go into the 4s orbital first (2 electrons) and then start filling 3d orbitals (9 electrons).
However, copper is a well-known exception to this rule. Instead of having 4s² 3d⁹, copper’s actual electron configuration is [Ar] 4s¹ 3d¹⁰. This happens because a fully filled d-subshell (3d¹⁰) is more stable than a partially filled one (3d⁹), and the atom gains extra stability by having a single electron in the 4s orbital and a completely filled 3d subshell.
Why is a full d subshell more stable? The full d subshell minimizes electron-electron repulsions and achieves a symmetrical electron distribution, which lowers the energy of the atom. The energy difference between 4s and 3d orbitals is very small and can be influenced by electron-electron interactions and exchange energy. Exchange energy is particularly significant in d orbitals due to their shape and overlap, making the completely filled 3d subshell energetically favorable.
Thus, copper “promotes” one electron from 4s to 3d to achieve this stable configuration. This phenomenon is also observed in other transition metals like chromium (Cr).
In summary, the noble gas notation for copper is:
Cu: [Ar] 4s¹ 3d¹⁰
This configuration reflects the subtle balance of electron energies and the special stability provided by completely filled d subshells in transition metals.