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Methanol as an example

The following example shows how to write the Lewis Dot Structure and the structural formula of methanol. The example also shows the molecular model assembled from a model kit and points out molecular shape, electron pair geometry and unshared electron pairs.

ch4o
This is the molecular formula for methanol. It shows that the methanol molecule consists of one carbon atom, 4 hydrogen atoms and one oxygen atom.
hydrogen
Hydrogen is found with the Group IA elements in the Periodic Table. Group IA elements have only one valence electron. In writing the Lewis Dot Structure for the hydrogen atom a single dot placed next to the symbol for hydrogen represents the one valence electron. Note that hydrogen may form only one covalent bond.
carbon
Carbon belongs to Group IVA. The four valence electrons are represented by 4 dots in the Lewis Dot Structure. By envisioning a box around the atomic symbol a single dot is placed on each side of the carbon symbol. Note that the four single electrons indicate that carbon may form 4 covalent bonds.
oxygen
Oxygen is found in Group VIA and has six electrons in its outer shell. The first four electrons are placed around the oxygen symbol singly, but the two additional electrons which are added result in two unshared pairs of electrons. The two single electrons indicate that oxygen may form 2 covalent bonds.
carbon-oxygen bond
Single electrons around the atomic symbol indicate the number of covalent bonds that that atom may form. Starting with the atoms that form the greatest number of bonds, carbon (4 bonds) and oxygen (2 bonds), create a single covalent bond between the two atoms represented by the pair of dots between the two atomic symbols. Note that there are 4 single electrons in this structure.
carbon-oxygen-hydrogen bond
Using one of the four hydrogen atoms, a single covalent bond between the carbon atom and a hydrogen atom may be created as shown by the pair of dots between the two symbols.
Lewis structure of Methanol
Three more single covalent bonds may be created with the three remaining hydrogen atoms. These bonds are formed between the single electrons in the Lewis Dot Structure.
structural formula of methanol
The Lewis Dot Structure for methanol may also be written as a structural formula by substituting dashes for the shared pairs of electrons. Each dash represents one pair of electrons (2 electrons total). Note that the unshared electron pairs are still shown in the structural formula.
molecular model of methanol
This is a photograph of methanol assembled from a model kit.
tetrahedral geometry around carbon
The black arrow is pointing out the black carbon atom. Note that there are four atoms bound to this carbon atom. The molecular shape around this carbon atom is tetrahedral. Because there are four groups of electrons around this carbon atom the electron pair geometry is also tetrahedral.
non-bonding pair of electrons
The yellow arrows are pointing out the unshared electron pairs associated with the oxygen atom. Each pair of unshared electrons is counted when determining the number of groups of electrons around the oxygen atom.
oxygen
The red arrow is pointing out the red oxygen atom. The oxygen atom is bound to two other atoms and has a bent molecular shape. Because there are four groups of electrons around the oxygen atom it has a tetrahedral electron pair geometry.
Use this animated model of methanol to better understand the tridimentional structure of this molecule.






Created and maintained by: Dr. Anna Cavinato anna.cavinato@eou.edu and Dr. David Camp
.
All Material Copyright Eastern ChemWeb, Eastern Oregon University, 2003.