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Introduction to Chemistry: 7.2 Lewis Dot Structures

Introduction to Chemistry
7.2 Lewis Dot Structures
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table of contents
  1. Cover
  2. Title Page
  3. Copyright
  4. Table Of Contents
  5. Introduction
  6. Preface
  7. Acknowledgements
  8. About the Authors
  9. Chapter 1. Chemistry: An Experimental Science
    1. 1.0 Introduction
    2. 1.1 Chemistry in Context
    3. 1.2 Phases and Classification of Matter
    4. 1.3 Physical and Chemical Properties
  10. Chapter 2. Atoms, Molecules, and Ions
    1. 2.0 Introduction
    2. 2.1 Atomic Theory
    3. 2.2 Beyond Dalton’s Atomic Theory
    4. 2.3 Atomic Structure and Symbols
    5. 2.4 Chemical Formulas
    6. 2.5 The Periodic Table
  11. Chapter 3. Ions, Bonding and Compound Formation
    1. 3.0 Introduction
    2. 3.1 Ionic and Molecular Compounds
    3. 3.2 Nomenclature of Simple Ionic and Molecular Compounds
  12. Chapter 4. Chemical Reactions and Equations
    1. 4.0 Introduction
    2. 4.1 Writing and Balancing Chemical Equations
    3. 4.2 Precipitation Reactions
    4. 4.3 Acid-Base Reactions
    5. 4.4 Oxidation-Reduction Reactions
  13. Chapter 5. Bridging the Macroscopic and Microscopic Realms
    1. 5.0 Introduction
    2. 5.1 Formula Mass
    3. 5.2 The Mole
    4. 5.3 Reaction Stoichiometry
    5. 5.4 Limiting Reactant and Reaction Yields
  14. Chapter 6. Solutions
    1. 6.0 Introduction
    2. 6.1 Solution Concentration and Molarity
    3. 6.2 Other Concentration Units
  15. Chapter 7. Chemical Bonding and Lewis Structures
    1. 7.0 Introduction
    2. 7.1 Covalent Bonding
    3. 7.2 Lewis Dot Structures
    4. 7.3 Lewis Structures and Covalent Compounds
  16. Additional Reading: Electronic Structure of Atoms
    1. 8.0 Introduction
    2. 8.1 Electromagnetic Energy
    3. 8.2 Quantization of the Energy of Electrons
    4. 8.3 Development of Quantum Theory
    5. 8.4 Electronic Structure of Atoms
    6. 8.5 Periodic Trends
  17. Chapter LAB1. Making Measurements
    1. Introduction
    2. LAB1.1 Expressing Numbers
    3. LAB1.2 Measurements and Units
    4. LAB1.3 Measurement Uncertainty, Accuracy, and Precision
    5. LAB1.4 Mathematical Treatment of Measurement Results – Unit Conversions
    6. LAB1.5 Density – A Derived Unit and Conversion Factor
  18. Appendix
  19. Appendix A: The Periodic Table
  20. Appendix B: Essential Mathematics
  21. Appendix C: Units and Conversion Factors
  22. Appendix D: Fundamental Physical Constants

29

7.2 Lewis Dot Structures

Learning Objective

By the end of this section, you will be able to:

  • Draw a Lewis electron dot diagram for any atom or a monatomic ion with an atomic number of less than 20.

In almost all cases, chemical bonds are formed by interactions of valence electrons in atoms. To facilitate our understanding of how valence electrons interact, a simple way of representing those valence electrons would be useful.

A Lewis dot structure is a representation of the valence electrons of an atom that uses dots around the symbol of the element. The number of dots equals the number of valence electrons in the atom. These dots are arranged to the right and left and above and below the symbol, with no more than two dots on a side. (It does not matter what order the positions are used.) For example, the Lewis electron dot diagram for hydrogen is simply

Hydrogen

Because the side is not important, the Lewis electron dot diagram could also be drawn as follows:

Hydrogen-Sides

The electron dot diagram for helium, with two valence electrons, is as follows:

Helium

By putting the two electrons together on the same side, we emphasize the fact that these two electrons are both in the first shell. The next atom, lithium, has three electrons total but only one electron in its valence shell. Its electron dot diagram resembles that of hydrogen, except the symbol for lithium is used:

Lithium

Carbon has four valence electrons. We draw the dots for the electrons on different sides. As such, the electron dot diagram for carbon is as follows:

With nitrogen, we distribute the five valence electrons around the atom, using four positions and not pairing up any electrons until necessary:

Nitrogen

Oxygen, with a total of six valence electrons, ends up with two unpaired electrons and two sets of paired electrons.

Oxygen

Fluorine and neon have seven and eight dots, respectively:

Fluoride-Neon

With the next element, sodium, the process starts over with a single electron because sodium has a single electron in its highest-numbered shell, the n = 3 shell.

Example 1

What is the Lewis electron dot diagram for each element?      a) phosphorous         b) argon

Solution

a) Phosphorous has five valence electrons, and argon has eight.  Phosphorus-Argon

Elements in the same column of the periodic table have similar Lewis electron dot diagrams because they have the same valence shell electron configuration. Thus the electron dot diagrams for the first column of elements are as follows:

First-Column

Lewis dot structures are particularly useful for describing covalent bonding in compounds. They are somewhat but less helpful for describing ions. As a reminder, covalent bonding occurs when nonmetal elements form bonds, so drawing covalent compounds with Lewis structures only requires drawing atoms of these nonmetal elements. Unless you want to delve deeper, there is no need to learn about drawing Lewis structures for metals and ions.

Key Concepts and Summary

Lewis dot structures represent atoms with their atomic symbol surrounded by valence electrons, which are represented as dots.  This type of symbolic representation can help describe compound formation, especially for covalent compounds.

Review-Reflect, Extend

Review-Reflect

1. What column of the periodic table has Lewis electron dot diagrams with two electrons?

2. Draw the Lewis electron dot diagram for silicon.

Extend

We know that water can be broken down into elemental hydrogen and elemental oxygen, and that the ratio of these gases that form is 2:1. Since both of these gases are diatomic (H2 and O2), water is made of H and O atoms in a 2:1 ratio as well. The observable properties of water indicate that these atoms are bonded together by covalent, rather than ionic bonds.

Draw Lewis dot structures for two hydrogen atoms and one oxygen atom. Attempt to arrange these three atoms so that they are sharing electrons. A finished “correct” structure should have every atom in the structure, once the sharing arrangements are made, with an electron arrangement that could be seen as “complete” or a “full shell.”

Answers to Review-Reflect

1. the second column of the periodic table

2.

Silicone

Annotate

Next Chapter
7.3 Lewis Structures and Covalent Compounds
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Chemistry
Copyright © 2020 by Carol Higginbotham. Introduction to Chemistry by Carol Higginbotham is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.
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