Project 8: Building Molecules: Dot Structure Expert 10 points
Objective: To Build the dot structures (or stick/dot structures) of 40 Molecules
Assignment: The student is to draw the dot or stick molecular structures of 37 compounds and three elements. This packet is to be submitted hard copy by last class meeting or electronically by last day of the term.
The Seven page dot structure data packet may be access at:
WORD .doc file dot structure packet:
Dot Structure Stick Structure
CHM 1020 Text
Suchocki 5th : Chapter 6 Section 6.5 Pages 173-177
CHM 1020 Video Reference:
Section 6.5 Covalent Bonds Result from a Sharing of Electrons (Four Videos)
a. Sharing Electrons Video #CO605Na (3:42 Minutes) http://bcove.me/neinvkxu
b. Covalent Bond Formation Video #CO605Nb (3:38 Minutes) http://bcove.me/93x3tys9
c. Water, Ammonia, and Methane Video #CO605Nc (5:10 Minutes) http://bcove.me/zmosl2wy
d. Multiple Covalent Bonds Video #CO605Nd (4:21 Minutes) http://bcove.me/5jh8hmus
In Section 6.5 our author does not list a process for drawing dot structures of molecules as in most text. He discusses what a single, double, and triple covalent bond is.
He states that a covalent bond consist of the sharing of one electron from each atom to make the bond. There is also what is called a coordinate covalent bond, where one atom provides both electrons to a shared pair.
He also discusses what a lone pair of electron is (or an unshared pair of electrons). He says that they do not have to be shown. For this project you have show the all the lone pairs.
He also favors the stick/dot method for drawing the structures. The following is an excellent table which shows you the variations on many nonmetals showing bonding via the octet rule. (Rule of 8).
A nonmetal, when bonding with another
have eight total electrons including the atoms original outer surface (valence)
electrons plus the electrons provided by the bonded atom. There are few exceptions:
1. Hydrogen follows the rule of two. (see table below)
2. Beryllium follows the rule of four.
3. Boron follows the rule of six (see table below)
The table leaves out some of the nitrogen (phosphorus, arsenic) variations in the rule of 8. Nitrogen has three bonds and a lone pair. There could be a double, single, and lone pair as a second variation. Nitrogen could also have a triple covalent bond and a lone pair as a third variation.
Most organic molecules follow the octet rule as carbon always has four bonds, never a lone pair (except carbon monoxide). We can us the octet rule for over 99% of the of the molecular structures.
However, most published books use the Mathematical method to determine the covalent bonding structures and sometimes even though the octet rule can be used to explain the structure. Sometimes structures of 10, 12, 14 or 16 electrons are around a single atom. For this course we will use the octet rule, the duet rule for hydrogen and the rule of six for Boron to keep it simple.
The mathematical process is shown at the end of this document, we will use your instructor’s rule of 8 method as follows:
Your instructor has paper atoms that which you may cutout and use to make your molecules for the assignment:
6: Paper Atoms
Dot/Stick Structures of Atoms (paper atoms):
Your Instructor’s Method for Drawing Dot Structures
The following is a modification of the mathematical approach**, where the octet rule is mainly used via seven steps: (** mathematical Approach is shown after the instructor’s method)
Never hook oxygen to oxygen except in peroxides, O2, O3(ozone).
a. Never have an unshared pair or lone pair of electrons on a carbon atom (except carbon monoxide, CO).
b. These are two dimensional structures, so there are many variations of the answer shown on the web site.
Never have more than two bonds to any oxygen
(except CO). If you place hydrogen to an oxygen, then
oxygen HAS to attach to another element by a single bond, never a double bond.
d. If you look carefully at the Dot Structure Data Page Packet you will find links to the answers.
e. Most of the
molecules that you will draw on the Dot Structure Data pages may be practiced
with the drag and drop molecule building web site. Access the menu at the
f. St. Olaf’s College has an interactive construct Lewis Dot Structure web site:
the Flash Player/plug in Lincoln-Sudbury Regional High School in Sudbury, Ma
the following Interactive Web Site to draw molecules:
high School teacher on Long Island, Mr. Kent, has Interactive chemistry web
The following will allow you to construct dot structures of some of the molecules in this
Drawing Dot Structures of Molecules via the Mathematical Method (Kotz 5th ):
Decide on the central atom
(usually not oxygen or hydrogen). The central atom is
usually the one with the lowest electron affinity. In formaldehyde, CH2O,
the central atom is carbon.
Determine the total number
of valence electrons in the molecules or the ion. In a neutral molecule this number will be the sum of the valence
electrons of each atom. For a negative ion add the charge to this total number.
For a positive ion subtract the positive charge from this total number. For CH2O:
C=4, H=1(x2) , O=6 this would be 4+2+6 = 12 total valence electrons.
Take this total number of
electrons and divide by two to determine the number of electron pairs. For CH2O: 12/2 = 6 electron
Place one pair of electrons
between each pair of bonded atoms to form a single bond. You can either show a pair of dots, or draw a single stick
between the two atoms to represent the single covalent bond
Use any remaining pairs as
lone pairs around each atom (except hydrogen) so that each atom is surrounded
by eight electrons. (There is never a lone
pair on a carbon except in Carbon monoxide)
6. If the central atom has fewer than eight electrons at this point, move one or more of the lone pairs on the terminal atoms in a position intermediate between the center and the terminal atom to form multiple bonds. (As a general rule double or triple bonds are formed when both atoms are from the following nonmetals: C, N, O, S. That is, bonds such as C=C, C=N, C=O, S=O will be encountered frequently.
Table 9.5 from Kotz displays common oxoacids and their anions:
Summary of Bishop’s Seven Steps to Draw Lewis Dot Structures:
Another Table from Hill 12th
From McMurray 5th Stick Benzene’s Structure: