Question

1. write the unabbreviated (full) electron configuration for the sulfide ion (s²⁻). which noble gas has this same configuration?
2. write the unabbreviated (full) electron configuration for a neutral atom of copper (cu). explain why this configuration is an exception to the aufbau principle.

Explanation:

Step1: Determine electrons in sulfide ion

Sulfur has atomic number 16. The sulfide ion ($S^{2 -}$) has 16+2 = 18 electrons.

Step2: Write electron - configuration

Using the Aufbau principle, the electron - configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}$.

Step3: Identify noble gas

The noble gas with 18 electrons is argon (Ar).

Step4: Determine electrons in neutral copper atom

Copper has atomic number 29, so a neutral Cu atom has 29 electrons.

Step5: Write electron - configuration of copper

The expected electron - configuration according to the Aufbau principle is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{9}$, but the actual configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{1}3d^{10}$.

Step6: Explain exception

Half - filled and fully - filled subshells have extra stability. In the case of copper, moving one electron from the 4s orbital to the 3d orbital gives a fully - filled 3d subshell ($d^{10}$) and a half - filled 4s subshell ($s^{1}$), which is more stable than the expected configuration.

Answer:

1. Electron configuration of $S^{2 -}$: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}$, Noble gas: Ar
2. Electron configuration of Cu: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{1}3d^{10}$. It is an exception because a fully - filled 3d subshell and a half - filled 4s subshell are more stable than the configuration predicted by the Aufbau principle.