Question

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Answer 1

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$\textbf{What is the Aufbau Principle?}$

The Aufbau principle dictates the manner in which electrons are filled in the atomic orbitals of an atom in its ground state. It states that electrons are filled into atomic orbitals in the increasing order of orbital energy level. According to the Aufbau principle, the available atomic orbitals with the lowest energy levels are occupied before those with higher energy levels.

EXCEPTIONS-:

Like most rules, there are exceptions. Half-filled and completely filled d and f subshells add stability to atoms, so the d and f block elements don't always follow the principle. For example, the predicted Aufbau configuration for Cr is 4s23d4, but the observed configuration is actually 4s(power1)3d(power5). This actually reduces electron-electron repulsion in the atom, since each electron has its own seat in the subshell.

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