EONS LEARNING

  • Home
  • About Us
  • Classroom
    • Resources >
      • Study Skills
      • Periodic Table
      • Common Ion Sheet
      • The Scientific Method
      • Doing Background Research
    • Introduction and Course Philosophy
    • Unit 1: Beginning Chemistry >
      • Lesson 1: The Atom >
        • What is an Atom?
        • The Structure of Atoms
        • The Periodic Table
        • Modeling Atoms
      • Lesson 2: Chemical Bonding >
        • Why Do Atoms Form Bonds?
        • Ionic Bonding
        • Covalent Bonding
        • Intermolecular Attraction
      • Lesson 3: Chemical Nomenclature >
        • Octet Rule
        • Ionic Compounds
        • Covalent Molecules
      • Lesson 4: Molecular Molecules >
        • Modeling Ionic Compounds
        • Modeling Covalent Molecules
      • Lesson 5: States of Matter >
        • States of Matter
        • Phase Changes
      • Lesson 6: Density >
        • What is Density?
        • Calculating Density
      • Lesson 7: Thermodynamics >
        • Temperature
        • Heat
        • Gas Laws
      • Lesson 8: Solution Chemistry >
        • Diffusion
        • Solutions and Molarity
        • Semi-Permeable Membranes
      • Lesson 9: Thermal Expansion >
        • Thermal Expansion
    • Unit 2: Earth Science >
      • Lesson 10: Earth at a Glance >
        • Perspective
        • Maps
      • Lesson 11: Layers of the Earth >
        • Layers of the Earth
      • Lesson 12: Plate Tectonics >
        • Plate Tectonics
      • Lesson 13: Rocks and Minerals >
        • Rocks and Minerals
      • Lesson 14: Particle Sorting >
        • Differentiation
        • Deposition of Sediment
      • Lesson 15: The Atmosphere >
        • Composition of the Atmosphere
        • Layers of the Atmosphere
        • Change Over Time
        • Atmospheric Disruption
    • Unit 3: The Cell >
      • Lesson 16: Life >
        • What is Life?
        • Structural Hierarchy of Living Things
      • Lesson 17: Biochemistry >
        • Intro to Biochemistry
        • Water
        • Micromolecules
        • Energy, Carbohydrates, Lipids
        • Protein and Nucleic Acid
      • Lesson 18: Cells >
        • What are Cells?
        • Microscopy
        • Plant and Animal Cells
      • Lesson 19: Membrane Transport >
        • A Special Environment
        • The Structure of Membranes
        • Membrane Transport
      • Lesson 20: Energy and Cell Respiration >
        • Energy in Biology
        • Energy Diagrams
        • Glycolysis and Anaerobic Respiration
        • Aerobic Cellular Respiration
      • Lesson 21: Photosynthesis >
        • Plants Get Energy From The Sun
        • Photosynthesis Process
        • Energy, Ecosystems, and the Environment
    • Unit 4: Anatomy and Physiology >
      • Lesson 22: The Human Body >
        • What Are Bodies Made Of?
        • What Do Bodies Do?
      • Lesson 23: The Nervous System >
        • The Nervous System
        • Neuronal Communication
        • The Central Nervous System
      • Lesson 24: The Endocrine System >
        • The Endocrine System
        • Hormones
        • Hormones, Puberty, and Reproduction
      • Lesson 25: The Integumentary System >
        • The Integumentary System
      • Lesson 26: The Musculoskeletal System >
        • The Skeletal System
        • The Muscular System
        • Anatomy Of The Musculoskeletal System
      • Lesson 27: The Cardiovascular System >
        • Blood and Blood Vessels
        • The Heart
      • Lesson 28: The Respiratory System >
        • The Respiratory System
      • Lesson 29: The Digestive System >
        • The Digestive System
        • Nutrition
      • Lesson 30: The Excretory System >
        • The Excretory System
      • Lesson 31: The Immune System >
        • Disease and Infection
        • Immunity
    • Units 5-6 Coming Soon
  • Workbench
    • Unit 1 >
      • EIS >
        • Lesson 1: Atoms
        • Lesson 2: Chemical Bonding
        • Lesson 3: Chemical Nomenclature
        • Lesson 4: Molecular Models
        • Lesson 5: States of Matter
        • Lesson 6: Density
        • Lesson 7: Thermodynamics
        • Lesson 8: Solution Chemistry
        • Lesson 9: Thermal Expansion
      • Unit 1: Project
      • Unit 1: Exam Review
      • Unit 1: Exam
    • Unit 2 >
      • EIS >
        • Lesson 10: Earth at a Glance
        • Lesson 11: Layers of the Earth
        • Lesson 12: Plate Tectonics
        • Lesson 13: Rocks and Minerals
        • Lesson 14: Particle Sorting
        • Lesson 15: The Atmosphere
      • Unit 2: Project
      • Unit 2: Exam Review
      • Unit 2: Exam
    • Unit 3 >
      • EIS >
        • Lesson 16: Life
        • Lesson 17: Biochemsitry
        • Lesson 18: Cells
        • Lesson 19: Membrane Transport
        • Lesson 20: Energy and Cell Respiration
        • Lesson 21: Photosynthesis
      • Unit 3: Project
      • Unit 3: Exam Review
      • Unit 3: Exam
    • Unit 4 >
      • EIS >
        • 22: The Human Body
        • 23: The Nervous System
        • 24: The Endocrine System
        • 25: The Integumentary System
        • 26: The Musculoskeletal System
        • 27: The Cardiovascular System
        • 28: The Respiratory System
        • 29: The Digestive System
        • 30: The Excretory System
        • 31: The Immune System
      • Unit 4 Project
      • Unit 4 Exam Review
      • Unit 4 Exam
    • Units 5-6 Coming Soon
  • Donate
  • Home
  • About Us
  • Classroom
    • Resources >
      • Study Skills
      • Periodic Table
      • Common Ion Sheet
      • The Scientific Method
      • Doing Background Research
    • Introduction and Course Philosophy
    • Unit 1: Beginning Chemistry >
      • Lesson 1: The Atom >
        • What is an Atom?
        • The Structure of Atoms
        • The Periodic Table
        • Modeling Atoms
      • Lesson 2: Chemical Bonding >
        • Why Do Atoms Form Bonds?
        • Ionic Bonding
        • Covalent Bonding
        • Intermolecular Attraction
      • Lesson 3: Chemical Nomenclature >
        • Octet Rule
        • Ionic Compounds
        • Covalent Molecules
      • Lesson 4: Molecular Molecules >
        • Modeling Ionic Compounds
        • Modeling Covalent Molecules
      • Lesson 5: States of Matter >
        • States of Matter
        • Phase Changes
      • Lesson 6: Density >
        • What is Density?
        • Calculating Density
      • Lesson 7: Thermodynamics >
        • Temperature
        • Heat
        • Gas Laws
      • Lesson 8: Solution Chemistry >
        • Diffusion
        • Solutions and Molarity
        • Semi-Permeable Membranes
      • Lesson 9: Thermal Expansion >
        • Thermal Expansion
    • Unit 2: Earth Science >
      • Lesson 10: Earth at a Glance >
        • Perspective
        • Maps
      • Lesson 11: Layers of the Earth >
        • Layers of the Earth
      • Lesson 12: Plate Tectonics >
        • Plate Tectonics
      • Lesson 13: Rocks and Minerals >
        • Rocks and Minerals
      • Lesson 14: Particle Sorting >
        • Differentiation
        • Deposition of Sediment
      • Lesson 15: The Atmosphere >
        • Composition of the Atmosphere
        • Layers of the Atmosphere
        • Change Over Time
        • Atmospheric Disruption
    • Unit 3: The Cell >
      • Lesson 16: Life >
        • What is Life?
        • Structural Hierarchy of Living Things
      • Lesson 17: Biochemistry >
        • Intro to Biochemistry
        • Water
        • Micromolecules
        • Energy, Carbohydrates, Lipids
        • Protein and Nucleic Acid
      • Lesson 18: Cells >
        • What are Cells?
        • Microscopy
        • Plant and Animal Cells
      • Lesson 19: Membrane Transport >
        • A Special Environment
        • The Structure of Membranes
        • Membrane Transport
      • Lesson 20: Energy and Cell Respiration >
        • Energy in Biology
        • Energy Diagrams
        • Glycolysis and Anaerobic Respiration
        • Aerobic Cellular Respiration
      • Lesson 21: Photosynthesis >
        • Plants Get Energy From The Sun
        • Photosynthesis Process
        • Energy, Ecosystems, and the Environment
    • Unit 4: Anatomy and Physiology >
      • Lesson 22: The Human Body >
        • What Are Bodies Made Of?
        • What Do Bodies Do?
      • Lesson 23: The Nervous System >
        • The Nervous System
        • Neuronal Communication
        • The Central Nervous System
      • Lesson 24: The Endocrine System >
        • The Endocrine System
        • Hormones
        • Hormones, Puberty, and Reproduction
      • Lesson 25: The Integumentary System >
        • The Integumentary System
      • Lesson 26: The Musculoskeletal System >
        • The Skeletal System
        • The Muscular System
        • Anatomy Of The Musculoskeletal System
      • Lesson 27: The Cardiovascular System >
        • Blood and Blood Vessels
        • The Heart
      • Lesson 28: The Respiratory System >
        • The Respiratory System
      • Lesson 29: The Digestive System >
        • The Digestive System
        • Nutrition
      • Lesson 30: The Excretory System >
        • The Excretory System
      • Lesson 31: The Immune System >
        • Disease and Infection
        • Immunity
    • Units 5-6 Coming Soon
  • Workbench
    • Unit 1 >
      • EIS >
        • Lesson 1: Atoms
        • Lesson 2: Chemical Bonding
        • Lesson 3: Chemical Nomenclature
        • Lesson 4: Molecular Models
        • Lesson 5: States of Matter
        • Lesson 6: Density
        • Lesson 7: Thermodynamics
        • Lesson 8: Solution Chemistry
        • Lesson 9: Thermal Expansion
      • Unit 1: Project
      • Unit 1: Exam Review
      • Unit 1: Exam
    • Unit 2 >
      • EIS >
        • Lesson 10: Earth at a Glance
        • Lesson 11: Layers of the Earth
        • Lesson 12: Plate Tectonics
        • Lesson 13: Rocks and Minerals
        • Lesson 14: Particle Sorting
        • Lesson 15: The Atmosphere
      • Unit 2: Project
      • Unit 2: Exam Review
      • Unit 2: Exam
    • Unit 3 >
      • EIS >
        • Lesson 16: Life
        • Lesson 17: Biochemsitry
        • Lesson 18: Cells
        • Lesson 19: Membrane Transport
        • Lesson 20: Energy and Cell Respiration
        • Lesson 21: Photosynthesis
      • Unit 3: Project
      • Unit 3: Exam Review
      • Unit 3: Exam
    • Unit 4 >
      • EIS >
        • 22: The Human Body
        • 23: The Nervous System
        • 24: The Endocrine System
        • 25: The Integumentary System
        • 26: The Musculoskeletal System
        • 27: The Cardiovascular System
        • 28: The Respiratory System
        • 29: The Digestive System
        • 30: The Excretory System
        • 31: The Immune System
      • Unit 4 Project
      • Unit 4 Exam Review
      • Unit 4 Exam
    • Units 5-6 Coming Soon
  • Donate

Modeling Covalent Molecules


In the previous lesson, you learned how to draw Lewis Dot Structures to show how cations give and anions receive an electron to complete their valence shells, and in that love, and the having and giving and sharing and receiving, we too can learn to have, and give, and share, and receive. In this lesson, you’ll learn how to do the same for the less give-and-take and more sharing-is-caring covalent compounds, which share a pair of electrons between two shells.

Lewis dot structures are the picture version of covalent molecules. A covalent bond is shown with a line, and leftover or nonbonded electrons are shown by a pair of dots. For all the molecules we’ll have you draw in this class, you will never ever end up with a single dot (a single nonbonded electron)--they will always come in pairs. There are exceptions to this rule, one of which we saw earlier with the air pollutant NO₂, but we won’t worry about them.
​
To draw lewis dot structures, follow these three simple (possibly, kind of complicated) steps:


  1. Draw the Lewis Dot structures of each atom in the molecule. You should remember these from when we made models for ionic bonding.
 
  1.  “Share Pair” the electrons in each structure (Circle 2 electrons, connecting two atoms) to indicate that two atoms “share” a pair of electrons. The ultimate goal is for each atom to have or share 8 electrons, or 2 electrons for hydrogen, giving them a stable noble gas configuration. Up to 3 pairs can be formed between two atoms; this represents a double bond or triple bond. Only use as many bonds as you need to give every atom an octet!
 
  1. Replace each pair of bonded electrons with a straight line. This represents a covalent bond. For double/triple bonds, use two or three parallel lines. Leave nonbonded pairs as dots. Make sure every dot has a pair! If it doesn't, you did it wrong.

Chlorine is a quick example. Each chlorine in Cl₂ (remember, this is a diatomic gas) has 1 nonbonded electron. They simply share that electron so that they both have an octet.
Picture
Oxygen is a somewhat tougher example. We see that when we move two electrons to the center to make a bond, each oxygen still only has (or thinks it has) 7 electrons, when really it wants eight. We also see that we have two nonbonded electrons that are not part of a lone pair. These are no-nos. So, we have to “share pair” again until we get a full octet on each, and no unpaired nonbonded electrons.
Picture
If we were to “share pair” again and we still didn’t have a full octet on each and/or we still had unpaired nonbonded electrons, we would have to “share pair” yet again to make it work. We see this in nitrogen (N₂, another diatomic gas):
Picture
If you ever end up with more than a full octet, at least for the examples you will see in this class (down farther on the Periodic Table we can sometimes see something called an expanded octet, but don’t worry about this for now), you’ll know you’ve made a mistake. If you can’t find that mistake easily, you’ll have to go back to the drawing board. It’s like solving a puzzle.

A Rule of Thumb for Covalent Bonding

Here's a little shortcut to what you just learned: for the molecules you will see in this class, the number of bonds an atom needs to form to make an octet is the same number of spaces it is from the last column of the periodic table. For example:
​
Group
Elements Included
Bonds Formed
Example With Structure
14
​C (sometimes Si)
4
​CO₂ --> O=C=O
15
​N, P
3
​N₂ --> N≡N
16
​O, S
2
​O₂ --> O=O
17 (aka halogens)
​F, Cl, Br, I
1
​Cl₂ --> Cl-Cl
hydrogen
H
1
​H​₂ --> H-H

​This is kind of like doing a little sneak preview of what the puzzle “should” look like when it’s done—and will hopefully help you to puzzle things together a little more quickly.

Summary

You should know:
  • How to draw Lewis dot structures for covalently bonded molecules, with single bonds, double bonds, and triple bonds.
  • How to tell if an atom has a noble gas configuration (octet) using Lewis structures.

As always, the more you practice with this, the easier it gets.

We will soon be leaving chemical bonding and reactions for a while to study the properties of matter. But, have no fear, your friend the molecule is still going to be with us to explain many of the properties of all ordinary matter.

Learning Activity

LA Modeling Covalent Molecules
File Size: 43 kb
File Type: pdf
Download File

This is another one of those things that you have to do in order to learn. After all, would you ever solve a jigsaw puzzle just by having someone tell you the basic rules of how to put together a jigsaw puzzle? Of course not! And this is just like that—I’ve given you the rules and some basic instructions, but now it’s your turn to actually learn how to draw molecular models.

For the following, you may draw out your answers in any format you like, but it is probably easiest to do them on a piece of paper.

For the following, draw the appropriate molecular structure. Some are standard nomenclature, and some are names that I had previously asked you to be familiar with; you may wish to review the associated nomenclature lesson. Be sure to include all lone pairs in your structures.

  1. Carbon dioxide
  2. Nitrogen (Remember HOFBrINCl!)
  3. Boron trifluoride (Hint: Boron is an exception. It’s “octet” is full with 6 electrons.)
  4. Methane
  5. Ammonia
  6. Water
  7. Sulfur hexafluoride (Hint: Sulfur can have an expanded octet. It will have 12 electrons in its valence shell in this structure.)
    
Challenge problem: Draw ethanol (C₂H₅OH) and briefly state where you might find it. Be sure to follow the drawing conventions we use in this class! (The same ones you have been using all lesson).
Lesson 5: States of matter
Picture
Lesson 4 exploration in science

Content contributors: Eli Levine, Nancy Jiang, Emma Moulton
© COPYRIGHT 2020. ALL RIGHTS RESERVED.