Electrons in Atoms and Ions

Unit 2: Atomic Theory                                                                                                              Reading: Chapter 5

Working Mode: Pairs                                                                                       Guided Instructional Activity 2-2

Learning Objective:  To practice the distribution of electrons according in an electron configuration notation and the orbital diagram.  To recognize the situations when energy considerations, Pauli’s principle and Hund’s Rule apply to the organization of electrons in atoms.

Background: For electron configurations essentially only the Aufbau Principle is employed.

Task 1: Write the Aufbau Principle in your own words in the space below.  You may also write the orbital filling order as well.

            Aufbau Principle:

            Filling order:

Task 2:  First indicate the number of electrons in the atom/ion, then write the electron configurations of the following elements or ions:

F:

Ca:

P:

Ti:

Mg²⁺:

O^2-:

Cu:

Fe³⁺: 

Br:

**Bi:

**Ra:

Orbital Diagrams

Background: An electron is a charged particle but also it is a magnetic particle.  Its magnetic “pole” is represented by its “spin.”  Electrons are negatively charged and always repel each other but are attracted to a positive charge.  The magnetic force (“spin”) is not as strong as the electronic force but electrons can correlate their magnetic forces so they are attracted (opposite magnetic forces) or further repelled (similar magnetic forces). Two electrons with an attractive arrangement of magnetic forces repel each other less and can reside in combination nearer to one another.  We call electrons in this situation electron pairs.  Both electrons in a pair can be equally attracted by the nucleus and it is their favorable attraction to the nucleus that allows them to occupy the same orbital even though they repel each other electrically.  Use the half arrow symbol to represent electrons.  The half arrow up and the half arrow down represent the different magnetic properties of the electron.  When the arrows are opposite the magnetic forces are attractive and when the arrows are the same (up or down) the magnetic forces are repulsive and the electrons cannot remain as pairs.

In this activity you will be writing orbital diagrams.  The Pauli Exclusion Principle  and Hund’s Rule are employed in writing these diagrams.

Task 3: In the space below write the Pauli Exclusion Principle  and Hund’s Rule in your own words. 

            Pauli Exclusion Principle:

            Hund’s Rule:

Task 4: Representing the electrons by half arrows, place the electrons these species have in the energy level diagram.  Base your organization on the comments above and that electrons prefer to occupy the lowest energy level that they can.

C                                      P                                  Mn                                           Cr (careful!)

___  ___  ___                   ___  ___  ___              ___  ___  ___  ___  ___          ___  ___  ___  ___ ___

___                                   ___                              ___                                          ___                             

___                                   [Ne]                             [Ar]                                          [Ar]     

Task 5: Explain why you arranged the electrons in the manner that you did.

C

P

Mn

Cr