Modeling Atoms with Lewis Dot Structures

Contributor: Hannah Brooks. Lesson ID: 12901

You have seen drawings of atoms with circles and little balls indicating electrons in their orbits. It would be hard to draw atomic bonds that way, but we will introduce you to a much easier method!

categories

Chemistry

subject
Science
learning style
Visual
personality style
Lion
Grade Level
High School (9-12)
Lesson Type
Quick Query

Lesson Plan - Get It!

Audio:

How are cities designed? Does it really matter what is located where? Does that affect how the city functions? What do atoms know about all this?

City designers consider the easiest ways to move people from one point to another.

Planners also consider where industries and services should be located in order to best serve the population. The location of these services is important to the ability of a city to function effectively.

Elements have electrons located in different layers, or shells, that are responsible for stability and chemical bonding. These electrons determine how easily an atom bonds with another element, much like accessing a public service in a city.

Remember, in an atom, electrons are found surrounding a dense nucleus. The number of electrons corresponds with the number of protons found in each nucleus. An element with 15 protons will have 15 electrons. These electrons are organized into levels, or layers, based on the size and shape of orbitals — either s, p, d, or f. Each shaped orbital holds a different number of electrons, but all atoms are trying to achieve a perfect octet of electrons. An octet is eight electrons in the outer level. However, elements have different numbers of valence electrons in the outer layer of the atom before bonding.

potassium atom

Potassium has one valence electron, a single electron located in the layer farthest from the nucleus.


Electron configurations are a helpful way to easily organize information about electron location, but they are difficult to use when trying to communicate how an atom bonds with another element. Scientists use Lewis dot structures to easily model the elemental state of electrons.

potassium lewis dot symbol

By Adrignola [CC0], from Wikimedia Commons

The single dot represents the single electron found in the outer level of the potassium atom. The chemical symbol for potassium is used to make reading the dot structure more efficient.

You can use electron configurations to determine how many valence electrons are found in atoms, or you can use a shortcut.

Download and print the Periodic Table from Downloadable Resources in the right-hand sidebar for reference as you continue.

Notice the values at the top — there is an A group and a B group. Use the numerical values associated with the A group to determine valence electrons. Group 1A has one valence electron, Group 2A has two. NOTE: This chart uses Roman numerals: IA, IIB, IIIA, etc.

  • How many valence electrons do you think 3A has?

Three, and so on. Group 8A has eight valence electrons.

  • What special rule does Group 8A satisfy?

The octet rule!

Group 8A is known as the noble gases. They are inert, meaning that they do not bond with other elements. They don't have to, because they already have eight electrons in the outer shell.

noble gases

The Lewis dot structure for a noble gas would have eight electrons, but you won't see a Lewis dot structure for a noble gas often!

Elements in groups 1A-7A will bond frequently, and are represented using the Lewis dot structure method. See if you can create a Lewis dot structure for boron (B) using your periodic table.

Boron is found in group 3A, so it will have three valence electrons. You should write the chemical symbol for boron in the middle, and place three dots around it. Try to place the dots in pairs when writing a dot structure. Check your work using this image:

Boron lewis dot symbol

By Adrignola [CC0], from Wikimedia Commons

Try a harder one, maybe sulfur (S).

Sulfur has six valence electrons, organized around the chemical symbol as shown below:

Sulfur lewis dot symbol

By Adrignola [CC0], from Wikimedia Commons

The number of valence electrons in the outer layer increases as you move across the periodic table. This will be an important concept to remember as you learn more about chemical bonding. Valence electrons are the part of the atom responsible for bonding, because they link together with the valence electrons from another element. These special electrons can be mapped using Lewis dot structures so you are able to visualize how the electrons are organized. Make a list of the steps to create a Lewis dot structure to review what you have learned.

In the Got It? section, you will make a prediction about how valence electrons and reactivity are related.

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