What is the Lewis Structure?
This method of drawing diagrams was named after Gilbert N. Lewis, an American physical chemist. It is used for displaying how atoms connect, creating chemical elements. It helps present a molecule visually. The atoms are shown in the form of the signs of chemical elements. Their electrons are presented in the form of dots around the signs. The pairs of dots help represent bonded atoms. However, to make the diagram easy to understand, the pairs of shared electrons, also known as covalent bonds, are replaced with lines. It's allowed to add two and three lines if atoms share several pairs of electrons.
Exercise 1: Lewis Structures and Molecular Modeling
Data Table 1. Lewis Structure and Molecular Model
Molecule or Ionic Compound | # of Valence Electrons | Lewis Structure INSERT HAND DRAWN STRUCTURE PICTURE HERE | VSEPR Model INSERT ACTUAL MOLECULAR MODEL PICTURE HERE |
CCl4 | 32 | | |
MgCl2 | 16 | | |
AlCl3 | 24 | | |
PbI4 | 32 | | |
CH4 | 8 | | |
ICl5 | 42 | | |
CH3OH | 14 | | |
CH3NH2 | 14 | | |
CH2CH2 | 12 | | |
CH2O | 12 | | |
NF3 | 26 | | |
H2O | 8 | | |
O2 | 12 | | |
CO2 | 16 | | |
H2O2 | 14 | | |
[NO2]- | 18 | | |
[NH4]+ | 8 | | |
SO2 | 18 | | |
NH3 | 8 | | |
H2S | 8 | | |
SF6 | 48 | | |
SbCl5 | 40 | | |
Valence Shell Electron Pair Repulsion Theory, or VSEPR Theory in More Detail
The VSEPR hypothesis helps understand how molecules look in the three-dimensional environment, which refers to actual life. Lone electrons and molecule bonds want to reduce repulsion. Accordingly, they always push away from each other because they have negative charges. The theory helps understand how different molecules arrange atoms when all connections and lone electrons repel. The theory helps understand the patterns of molecules in real life. Depending on the number of atoms and sets of lone electrons circling the central atom, a molecule gets a particular shape.
Data Table 2. VSEPR Names and Atoms
Molecule | Number of atoms or sets of lone pairs surrounding central atom | Structure Geometry (Name) |
CCl4 | 4,0 | tetrahedral |
MgCl2 | 2,0 | linear |
AlCl3 | 3,0 | Trigonal planar |
PbI4 | 4,0 | tetrahedral |
CH4 | 4,0 | tetrahedral |
ICl5 | 5,1 | Square pyramidal |
CH3OH | 4,0 | Tetrahedral |
CH3NH2 | 4,0 | tetrahedral |
CH2CH2 | 3,0 | Trigonal planar |
CH2O | 3,0 | Trigonal planar |
NF3 | 3,1 | Trigonal pyramidal |
H2O | 2,2 | bent |
O2 | 1,2 | linear |
CO2 | 2,0 | linear |
H2O2 | 2,2 | bent |
[NO2]- | 2,1 | bent |
[NH4]+ | 4,0 | tetrahedral |
SO2 | 2,2 | bent |
NH3 | 3,1 | Trigonal pyramid |
H2S | 2,2 | bent |
SF6 | 6,0 | Octahedral |
SbCl5 | 5,0 | Trigonal bypyramidal |
Questions:
A) Which, if any, of the molecules in Data Table 1 had resonance structures? How many resonance structures did the molecule(s) have?
SO2 AND [NO2]-which both have two resonance structures
B) The sulfur molecule was denoted by a yellow colored molecular modeling piece. Why is the color yellow a great visual example of the sulfur molecule? Note: You may need to research properties of sulfur to answer this question.
This is because sulfur as an element is bright yellow solid in crystalline form at room temperature hence representing it in yellow as a model gives visual impression characteristic to the element.
C) Ozone (O3) is a chemical that is considered a pollutant and is toxic when it appears in the air that we breathe. It is produced as a by-product of the exhaust of combustion engines reacting with the oxygen in air, in the presence of sunlight. However, in the upper layers of the atmosphere, ozone is beneficial as it blocks damaging ultraviolet radiation from reaching the Earth’s surface. Draw the Lewis structure of O3, including any resonance forms.
D) Lewis structures are drawn for molecules and not typically for ionic compounds. Explain why Lewis structures are not typically drawn for ionic compounds.
Ionic compounds do not involve sharing of electrons between bonding pairs unlike molecules. One atom completely loses an electron(s) and the other gains completely for the ionic compounds.
Summary Paragraph:
Lewis structures illustrate arrangements of electrons in an atom, compound or molecule. Valence shell electron pair repulsion model shows the structure of a molecule in three dimensions. It illustrates how the atoms are arranged attached and oriented to the given direction.
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