Methane has a chemical formula of CH4. The Lewis structure is shown below.

First, determine which atom is the central atom.

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Second, determine the number of electron-dense areas that are attached to the central atom.

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Correct! There are four electron-dense areas around the central carbon atom. To help you count these electron-dense areas, draw balloon-shaped structures around each electron-dense area.

Incorrect. There are four electron-dense areas around the central carbon atom. To help you count these electron-dense areas, draw balloon-shaped structures around each electron-dense areas.

Let's look at another example.

The chemical formula for formaldehyde is CH2O. The Lewis structure is shown below.

First, determine which atom is the central atom.

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Second, determine the number of electron-dense areas that are attached to the central atom.

Enter number here:

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Correct! There are three electron-dense areas around the central carbon atom. To help you count these electron-dense areas, draw balloon-shaped structures around each electron-dense area.

Incorrect. There are three electron-dense areas around the central atom. Remember, double or triple bonds count as only one area. Also, only count the electron-dense areas attached to the central atom. In this example, the lone pairs on the oxygen atom are not counted because it is not the central atom. To help you count these electron-dense areas, draw balloon-shaped structures around each electron-dense area.

Let's look at one last example.

The chemical formula for ammonia is NH3. The Lewis structure is shown below.

First, determine which atom is the central atom.

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Second, determine the number of electron-dense areas that are attached to the central atom.

Enter number here:

Submit

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Correct! There are four electron-dense areas around the central carbon atom. The lone pair counts as an electron-dense area since the pair is attached to the central atom. To help you count these electron-dense areas, draw balloon-shaped structures around each electron-dense area.

Incorrect. There are four electron-dense areas around the central atom. The lone pair counts as an electron-dense area since the pair is attached to the central atom. To help you count these electron-dense areas, draw balloon-shaped structures around each electron-dense area.