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Learn the octet rule and how it applies to electron energy levels. Identify valence electrons and learn how to determine them by looking at the periodic table. Also, discover how they pertain to the octet rule.

Learn how to draw the Lewis diagram of an atom, and understand how it provides clues to chemical bonding.

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Octet Rule

Before we start this lesson on Lewis dot structures and the octet rule, let’s review a bit. Atoms are composed of protons and neutrons that live in the nucleus and electrons that orbit the nucleus in energy levels. The periodic table is an organized way of categorizing all the elements. Remember that the letter in each square of the periodic table is an abbreviation of the element.

The number up above the letter is the atomic number and also the number of electrons. The number under the letter is the atomic mass.

Atoms bond to fill their outer electron shells.
Helium in group VIIIA is the only exception.

It has only two valence electrons.Once you know how many valence electrons there are, that’s how many dots you put around the symbol. The dots go on all four sides of the letter symbol. Put a single dot on each side (up to four electrons), then pair them up if you have more.For example, fluorine (F) is in group VIIA; therefore, it has seven valence electrons.

It is written with a capital F with seven dots around it. How about oxygen in group VIA? What do you think it looks like as a Lewis dot structure? That’s right:

Examples of Lewis dot structures for elements
Lewis Dot Structure Examples

Chemical Bonding

A Lewis dot structure makes it easy to see when an element would want to bond with another element. By quickly looking at the dots around the symbol, you can see if the outer shell of that element is full. If it isn’t full, you know it is going to want to chemically bond with another element.

A Lewis dot structure illustrating the chemical bond between two elements
Lewis Dot Bonding

Look at fluorine again. You know that it isn’t full because of that lone dot.

Fluorine is going to want to bond, possibly with another fluorine, so it can fill that empty spot. Two elements that are bonded with shared electrons can be shown like this: F:F. Or, with a line between them to show that they have a chemical bond: F-F. Elements can form more than one bond between them, but that’s a lesson for another time.

Lesson Summary

So, to review: A valence electron is an electron in the highest energy shell of an atom, and the octet rule says that atoms like to have full valence shells of eight electrons. A Lewis dot diagram shows the valence electrons in an atom by representing them as dots arranged in pairs around the letter abbreviation for the element.

Learning Outcomes

Following this video, you will be able to:

  • Define Lewis dot structures and the octet rule
  • Understand the relationship between the octet rule and valence electrons
  • Identify and determine valence electrons
  • Draw Lewis dot structures
  • Explain why Lewis dot diagrams are important in understanding chemical bonding

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