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General Chemistry Collection
Writing Electron Dot Structures
Mac OS– and Windows-compatible computers
User’s Guide
Introduction
Hardware and Software Requirements
Installation
Getting Started
User Directions
Steps for Electron Dot Structures
Troubleshooting
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Writing Electron Dot Structures
Writing Electron Dot Structures
Kenneth R. Magnell
Department of Chemistry, Central Michigan University, Mt. Pleasant MI 48859
Introduction
Writing Electron Dot Structures is a computer program for Mac OS and Windows that provides drill with feedback for students learning to write electron
dot structures. While designed for students in the first year of college general
chemistry it may also be used by high school chemistry students.
A systematic method similar to that found in many general chemistry texts is
employed.
1.
Determine the number of valence shell electrons.
2.
Select the central atom.
3.
Construct a skeleton.
4.
Add electrons to complete octets.
5.
Examine the structure for resonance forms.
During the construction of a structure, students have the option of quitting,
selecting another formula, or returning to a previous step. If the “select another
formula” option is chosen, the user will be informed of the status of available
formulae for the session (structures attempted but not completed, structures
completed and structures not attempted).
If an incorrect number of electrons is entered, students may not proceed until
the correct number is entered. The symbol entered for the central atom must
follow accepted upper- and lowercase practice, and entry of the correct symbol
must be accomplished before proceeding to the next step. A periodic table is
accessible and feedback provides assistance for these steps.
Construction of the skeleton begins with the placement of the central atom.
Atoms can be added, moved, or removed. Prompts and feedback keep students
informed of progress and problems. A correct skeleton is required before proceeding to the next step.
Completion of the structure begins with the addition of electron pairs to form
the required bonds. Remaining electrons are added to complete the formation
of multiple bonds, assure compliance with the octet rule, and form expanded
octets. Resonance forms are made by moving or removing and replacing electron pairs in the existing skeleton. Prompts and feedback guide students through
this process. A running tally of bond pairs, unshared pairs, octets, electrons
used, and electrons remaining is provided during this step.
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Writing Electron Dot Structures
Writing Electron Dot Structures requires the following software, which is available for free download from the Internet: Netscape Navigator, version 4.75 or
higher, or Microsoft Internet Explorer, version 5.0 or higher, and Shockwave
Player (available from Macromedia).
Hardware and Software Requirements
Hardware and software requirements for Writing Electron Dot Structures are
shown in Table 1.
Table 1. Hardware and software requirements for Writing Electron Dot Structures.
Computer
CPU
RAM
Drives
Graphics
Operating
System
Other Software
Mac OS
Compatible
Power
Mac
≥ 64 MB
CD-ROM;
Hard Drive
≥ 256 colors;
≥ 800 × 600
System 8.6 or
higher
Internet Browser such as Netscape Navigator
or Internet Explorer; Shockwave Player
Windows
Compatible
Pentium
≥ 64 MB
CD-ROM;
Hard Drive
SVGA;
≥ 256 colors;
≥ 800 × 600
Windows XP,
2000, ME, 98
Internet Browser such as Netscape Navigator
or Internet Explorer; Shockwave Player
Installation
Installation instructions for the General Chemistry Collection CD-ROM are
found in the ReadMe.wri file (Windows) or Read Me First! file (Mac OS) located
at the root level of the General Chemistry Collection CD-ROM and in the General Chemistry Collection User’s Guide, User_Dir.pdf, located in the Documentation folder. Writing Electron Dot Structures is run directly from the CD. For
Windows users, shortcuts to start Writing Electron Dot Structures are included
in the Typical installation for the CD or may be installed separately using a
Custom installation.
Writing Electron Dot Structures requires the following software, which is available for free download from the Internet:
•
Netscape Navigator; version 4.75 or higher;
URL: http://channels.netscape.com/ns/browsers/default.jsp (accessed May
2003).
OR
•
Microsoft Internet Explorer; version 5.0 or higher;
URL: http://www.microsoft.com/windows/ie/default.asp (accessed May 2003).
AND
•
Shockwave Player; version compatible with your OS and browser;
URL: http://sdc.shockwave.com/shockwave/download/. (accessed May 2003).
After downloading these installers, follow the directions provided to install the
new software.
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Writing Electron Dot Structures
Getting Started
Windows
To start Writing Electron Dot Structures, click the Start button, then select JCE
Software from the Programs menu. From the JCE Software menu select General Chemistry Collection, then Writing Electron Dot Structures. From the Writing Electron Dot Structures submenu, select Writing Electron Dot Structures.
Alternatively, locate and double-click the EDSpc.htm icon inside the Writing Electron Dot Structures folder.
Mac OS
Double-click the icon for EDSpc.htm, or open the file in your Internet browser.
All Users
Your WWW browser will open, Shockwave player will be loaded. On the opening
title screen, shown in Figure 1, click the Start button in the lower right corner.
A Welcome screen, shown in Figure 2 appears. Read the information about
Writing Electron Dot Structures, then click the Continue button in the lower
right corner.
Figure 1. The title screen of Writing Electron Dot
Structures.
User Reproducible
Figure 2. The Welcome screen describes the program.
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Writing Electron Dot Structures
After the Welcome screen, a screen containing General Instructions for using
the program appears, as shown in Figure 3. If you are unfamiliar with Writing
Electron Dot Structures, you should read these instructions carefully. When
you are finished click the Continue button in the lower right corner. The Main
Menu for Writing Electron Dot Structures, shown in Figure 4, appears. Click
any labelled button to begin working on the electron dot structure (EDS) for
that molecule or ion.
Figure 3. General Instructions for Writing Electron Dot Structures.
Figure 4. The Main Menu allows you to select the
molecule or ion for which you will determine the
electron dot structure.
On-screen help is available on many screens by clicking the Program Help button at the bottom of the screen, as shown in Figures 8–10 and 12–14.
You can quit the program at any time, by quitting the browser by selecting Quit
(Mac OS ) or Exit (Windows) from the browser’s File menu. Or, you can simply
close the browser window that contains Writing Electron Dot Structures, and
open a new window to continue using the browser.
User Directions
After selecting a molecule to work with from the Main Menu (see Fig. 4) follow
the directions on the screen to complete the electron dot structure for the compound. If you make an error, you will be informed, and assistance will be provided. Figures 5–11 illustrate the process for beryllium difluoride.
The RECYCLING BIN shown in Figures 8–15 can be used to remove atoms (Figs.
9–12) or pairs of electrons (Figs. 12–15) from the structure. Hold down the shift
key while you click the item you wish to remove from the structure and drag it
to the RECYCLING BIN. The program will prompt you to select a new location if
an atom was recycled, or return removed electrons to the tally at the top of the
window.
When you have completed a structure, or at any other time, you can return to
the Main Menu by clicking the Try Another EDS button. You can start over with
the same molecule or ion by clicking the Try this EDS Again button, or try the
same structure with a different arrangement of atoms by clicking the Try Another Skeleton button. Many different equivalent skeletons are possible for
each molecule or ion.
If you return to the Main Menu, you will find the buttons for any molecules or
ions whose structures you have successfully completed are colored green. Any
that you have attempted, but not successfully completed are colored blue.
User Reproducible
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Writing Electron Dot Structures
Figure 5. Enter the number of valence electrons in
the text box, then hit the return or Enter key. Click
the Periodic Table button to display a periodic
table that you can use to determine the number of
valence electrons for each atom.
Figure 6. If the number is correct, you will be asked
to identify the central atom. Type its symbol in the
text box, then hit the return or Enter key.
Figure 7. When you have identified the central
atom, you can click Review This Step to review
your work so far, or click Go To The Next Step to
continue.
Figure 8. Click the box in the center of the array
to place the symbol of the central atom.
Figure 9. Place the remaining atoms around the
central atom by clicking empty boxes. Adjacent
boxes can only be used if more than four atoms
surround the central atom.
User Reproducible
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Writing Electron Dot Structures
User Reproducible
Figure 10. In this example, the F atoms were placed
on either side of the Be atom. To check the skeleton
click the Click here to Check Skeleton button.
Figure 11. When you have an acceptable skeleton,
you can proceed to the steps in which electrons are
added. On-screen instructions are available by clicking the YES button. Click NO or press the return or
Enter key to go directly to the next step.
Figure 12. Add pairs of electrons to the skeleton by
clicking between atoms to form bonds and on atoms to add unshared electrons. If you make an error, help will be provided. A running total of the
electrons used is kept in the upper right corner of
the screen.
Figure 13. You can move electron pairs by clicking
and dragging while holding down the shift key.
When you have added all the electrons and are
satisfied with their positions, click the Click here
to Check Structure button.
Figure 14. If your structure is acceptable, you will
be asked if there are resonance structures for the
molecule. Click YES or NO. If there are resonance
structures, you must move electrons in the present
structure to form them. In this example, BeF2 has no
resonance structures.
Figure 15. When the structure and any resonance
forms are complete, you will be informed.
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Writing Electron Dot Structures
Steps for Electron Dot Structures
Use the following steps to write the electron dot structure of a molecule or a
polyatomic ion.
1.
Write the formula of the molecule or ion.
2.
Count the electrons available: the total number of valence shell electrons. Each atom in the molecule or ion contributes the electrons in the
outermost s and p orbitals. Remember that all of these must appear in
the final structure.
3.
Draw the skeleton. This is the central atom(s) with all of the outer atoms
arranged around it (them).
4.
If not indicated, the central atom is an atom of the element which:
• Is not H or F.
• Is not O, Cl, Br, or I unless the only other atoms are H, O, or halogens.
• Is least numerous in the molecule or ion.
• Is the largest in the molecule or ion (usually furthest toward the lower
left side of the periodic table).
• Has the highest bonding capacity (again, usually furthest toward the
lower left side of the periodic table).
5.
Add enough bonds (pairs of electrons) to hold the molecule or ion together. Limit bonds to one pair of electrons per pair of bonded atoms. A
bond should be between a central atom and an outer atom or between
two central atoms, but not between two outer atoms.
6.
Some atoms now will have complete octets (surrounded by four pairs of
electrons). Use the remaining electrons (you must use all of those counted
in Step 2) to complete octets surrounding the remaining atoms. It is usually best to add unbonded electron pairs to all of the outer atoms before
adding any to the central atom(s).
7.
Carefully check your count of electrons. If all atoms in the structure (with
the exception of H, Li, Be, or B) are surrounded by octets, the structure is
complete. If not, complete it by using one of the following:
a. If some octets are incomplete and all of the electrons have been used,
rearrange the electron pairs so that some pairs of atoms are joined
with more than one pair of electrons—multiple (double or triple) bonds.
This is usually accomplished by moving unshared pairs on the outer
atoms into a bonding position. Do not make multiple bonds with either H or F.
b. If all of the atoms are surrounded by an octet and electrons are left
over, add the remaining electrons to the central atom. This will result
in a central atom with more than eight electrons—a situation called
an “expanded octet”. Note that expanded octets do not occur when the
central atom is C, N, or O.
If it is not possible to satisfy the conditions in Step 7, check your count of valence electrons in Step 2. If your count was correct, consult your instructor.
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Writing Electron Dot Structures
Troubleshooting
If you experience any difficulty in running Writing Electron Dot Structures,
first verify that you have the minimum hardware and software required to run
the program. Hardware and Software requirements for Writing Electron Dot
Structures may be found on Page 3.
Problem Reports
If the problem is not addressed in the User’s Guide and all required hardware
and software are present and in working order, contact the JCE Software office
for technical assistance. For quickest response, call, send a FAX, or an email
message.
Telephone: 800-991-5534 (USA only) or 608-262-5153
FAX: 608-265-8094
Email: [email protected]
Regular office hours are Monday–Friday, 9:00 a.m. to 5:00 p.m. (Central Time).
An answering machine is available at all times. Your message should include
the following information:
• Your name
• How we may contact you (telephone number or email address)
• The best time to reach you by telephone
• Title of the program
• A description of the problem
• A description of your computer system (model, RAM, operating system version, etc.)
If you do not receive a response to a telephone message or email within two
working days, please contact the office again during office hours and request
that your call be transferred (or email message be forwarded) immediately to a
technical editor.
Online Assistance
A technical support section is available on our WWW site at
http://jchemed.chem.wisc.edu/JCESoft/ where you will find a list of technical
questions we have received and answers or solutions for each program we publish. Also, JCE Forums, http://jchemed.chem.wisc.edu/cgi-bin/webx, includes
online discussions of JCE Software publications. If you have WWW access, it
may save you time to check these sites first if you encounter any difficulties.
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