Chapter 7, Problem 7.87QP

Interpretation Introduction

Interpretation:

The role of Aufbau principle which plays in classifying the elements in the periodic table should be explained.

Concept Introduction:

An orbital is a region of space in which electrons are filled.  It can hold up to two electrons.

An atomic orbital is the region of space in which the probability of finding the electrons is highest.  It is subdivided into 4 orbitals such as s, p, d and f-orbitals which depend upon the number of electrons present in the nucleus of a particular atom.

The orders in which orbitals are filled by the electrons are governed by three basic principles.

1. 1. Aufbau principle: In the ground state of an atom, an electron enters the orbital with lowest energy first and subsequent electrons are fed in the order of increasing energies. The word 'aufbau' in German means 'building up'. Here, it refers to the filling up of orbitals with electrons.  Aufbau principle explains the theoretical, sequential building up of the stepwise addition of protons and electrons for the elements in the periodic table.
2. 2.

Figure 1

1. 3. Pauli Exclusion Principle: As an orbital can contain a maximum of only two electrons, the two electrons must have opposing spins.
2. 4. Hund’s rule: Every orbital in a subshell is singly occupied with one electron before any one orbital is paired and all electrons in singly occupied orbitals have the same spin.

The electron configuration is the distribution of electrons of an atom or a molecule in various atomic orbitals.  By following these three principles, electronic configuration of a particular atom is written.

Aufbau principle “build” the periodic table of the elements and decide their electron configurations by steps.  Each step involves the addition of one proton to the nucleus and one electron to the appropriate atomic orbital.  The roles of Aufbau principle in classifying the elements in the periodic table are explained by taking the particular elements as examples.