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Bonding and Bond Formation

by Richard Paselk

Ratings

Overall Rating:
Content Quality:
Effectiveness:
Ease of Use:

Reviewed:	Jul 18, 2007 by Chemistry Editorial Board
Overview:	A simple discussion of the nature of ionic and covalent bonding is presented for the general chemistry audience. However, what makes this site so very different is the inclusion of quicktime movies showing the before and after bonding quantum mechanical views of the distribution of electron density. This gives a powerful understanding to the students of the nature of the electron redistribution during bonding.
Learning Goals:	This site will give students a detailed pictorial understanding of the change in electron distribution during ionic and covalent bonding.
Target Student Population:	Student of general chemistry studying the different kinds of bonding.
Prerequisite Knowledge or Skills:	Students should have a basic knowledge of atomic electron configurations. A modest grasp of what happens when two atoms bond would also be useful.
Type of Material:	Text material is supplemented with single images, which are links for QuickTime animations of the elctron density and quantum mechanical elctron probability distribution graphs for the formation of ionic and covalent bonds.
Recommended Uses:	This site will be useful as a supplement to a textual or verbal description of bonding when discussing the rearrangement of electron distribution that accompanies the formation of ionic and covalent bonds.
Technical Requirements:	The application requires the availability of quicktime as a movie player. Because small movie clips are being downloaded, a high speed internet connection is preferable.

Evaluation and Observation

Content Quality

Rating:

Strengths:

1. The incorporation of quantum mechanical calculations into the visualization of bonding is very powerful. This site is a 'must use' for teachers when discussing bonding. The example of covalent bond formation for the H₂ molecule is particularly compelling.

The simulations differentiate between core and valence electrons. The text highlights information that should be gleaned from the simulations.

Concerns:

1. The descriptive text is a little brief. There could be some improvement in word-smithing to better address the student needs i.e. better introduction, better transition between thoughts etc.

2. A grid system would help the viewer identify what is happening to the image. The first images are translational but some of the later images are rotational motion and it is difficult to identify what is happening on the simulation.

3. Also, some discussion should be included to indicate that unless energy is removed from the system, bonding will not occur. From the student standpoint, they expect to see bonding occur, so they need to know how energy conservation plays into this. The excess energy will appear as vibrational or rotational components and this should be more clearly described and presented to the student.

Potential Effectiveness as a Teaching Tool

Rating:

Strengths:	The teacher can do no better than to use these animations when discussing the different kinds of bonding. The change in electron density about the sodium atom in the formation of NaCl is very clearly evident and provides perspectives that teachers simply cannot do apart from the high quality calculations presented by these movies.
Concerns:	1. The motions of the atoms are fairly rapid and it is sometimes difficult and subtle to see the bonding effects described in the text. 2. The use of the Morse potential curve really requires more detailed explanation as to where the energy released upon bond formation 'goes'.

Ease of Use for Both Students and Faculty

Rating:

Strengths:	The simulations that open do so easily and quickly. The web page is very easy to use. Some of the quick time movies are quite large.
Concerns:	The layout of the page is a scrolled page with no attention being paid to general layout.

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Peer Review

Bonding and Bond Formation

Ratings

Overall Rating:

Evaluation and Observation

Content Quality

Potential Effectiveness as a Teaching Tool

Ease of Use for Both Students and Faculty