The process of successive addition of protons to the nucleus followed by an addition of the same num — Atomic Structure Chemistry Question

💡 Solution & Explanation

### Step 1 - Core Principle of Building Up Electronic Configurations The process of constructing the electronic configuration of a multi-electron atom in its ground state is based on conceptually adding protons one by one to the nucleus, while simultaneously adding an equal number of electrons to the available atomic orbitals in increasing energy order. This is named after the German word *Aufbauen* meaning "to build up" — the **Aufbau principle**. ### Step 2 - The $(n+l)$ Rule for Orbital Energy Order Under the Aufbau principle, orbital filling order follows the $(n+l)$ rule: * Lower $(n+l)$ value → filled first * Equal $(n+l)$ → lower $n$ filled first $$\ce{1s} \rightarrow \ce{2s} \rightarrow \ce{2p} \rightarrow \ce{3s} \rightarrow \ce{3p} \rightarrow \ce{4s} \rightarrow \ce{3d} \rightarrow \dots$$ ### Step 3 - Analysis of Options * **Option (A) Pauli exclusion principle:** Limits each orbital to max 2 electrons with opposite spins — constrains capacity within an orbital, does not define the cross-subshell filling order. Incorrect. * **Option (B) Hund rule:** Governs filling within degenerate orbitals of the same subshell — not the overall sequential order across energy levels. Incorrect. * **Option (C) Heisenberg uncertainty principle:** $\Delta x \cdot \Delta p \ge \frac{h}{4\pi}$ — relates to position-momentum measurement, not electronic configuration construction. Incorrect. * **Option (D) Aufbau principle:** Directly defines the sequential proton+electron addition process in increasing energy order to obtain ground-state configuration. Correct. $$\text{Correct Option: } \boxed{\text{D}}$$