Essay Sample on Molecular Modeling and Lewis Dot Structures

VSEPR Theory and Molecular Geometry
VSEPR Theory and Molecular Geometry

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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