Chapter 7, Problem 7.91QP

Interpretation Introduction

Interpretation:

The ground-state electron configuration of selenium ($\text{Se}$) has to be written using Aufbau principle.

Concept introduction:

By using Aufbau principle, electrons starts to occupy from orbitals of lower energy level.  Thus, the obtained lower energy configuration is known as ground-state electron configuration.

Aufbau principle:

• Electrons first occupy orbitals with lower energy than higher energy.
• An orbital can be occupied only by two electrons having opposite spins.
• Greater the number of parallel spins of electrons more stable the orbital.  Each electron fills each orbital till it is half filled.  This is known as Hund’s rule.
• The order of electrons filling in an atom is given as

Figure 1

Pauli Exclusion Principle:

It states that in an atom no two electrons have same quantum numbers.  That is two electrons in an atom can have same three quantum number ($\text{n,}\text{l,}{\text{m}}_{\text{l}}$) but the spin quantum number differs because of electrons in same orbital spins in opposite direction.