How do you build a Lewis Structure (chemistry)?

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udonbutterfly's profile pic

udonbutterfly | Student, College Freshman | (Level 1) Valedictorian

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In order to build a Lewis Structure you must first must identify your central element then count the amount of valence electrons that are present in the compound

For example, CH4 There are a total of 8 valance electrons.

No you have to check whether central atom will need an octet, double bond, or not. Since it's carbon we know it needs an octet/

The image shows C fulfilling an octet as well as the right number of electrons.

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thewanderlust878's profile pic

thewanderlust878 | Student, College Freshman | (Level 3) Salutatorian

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There are four steps that are usually taken in order to build a lewis structure. There is a possible 5th step, but it is usually only used when you need a formal charge for another question, outside of simply building the structure. The steps are as follows:

  1. count the total number of valence electrons (based on the periodic table) for each of the atoms. Then account for the extra charges, add electrons for negative and subtract for positive charges
  2. Build the structure with single bonds. You may need to know how atoms attach together before you begin. Then add extra electrons (dots) around the outer elements/compounds
  3. Then count the electrons you have placed. If there are more electrons than you have placed on the structure already, then add the remaining number to the central atom. 
  4. If the octet rule is not fulfilled by the single bonds, lone pairs around the outer atoms and around the central atom, begin putting double and triple bonds on.
  5. If need be, find the formal charge of the each atom as a double-check or to answer other questions. 

Hope this helps!

ckung's profile pic

ckung | Student, Grade 11 | eNotes Newbie

Posted on

To build a Lewis Structure, 5 crucial steps are needed.

1. Take the molecule and make a "skeleton" structure. What this means is that you want to take the elements involved in the molecule and arrange them appropriately. Tips for arranging are that the central atom is usually the atom with the most valence electrons or is the least electronegative and all other elements are attached to the central atom.

2. Find out the total number of valence electrons by adding the valence electrons of each element together. If there is a charge on the molecule, add an electron if the charge is negative and subtract if its positive.

3. Draw bonds connecting the central element to the other elements, which are essentially the outside elements. Remember that each bond consists of 2 valence electrons.

4. With the remaining valence electrons, place them on the outside elements to make sure each of them has a full octect.

5. If there are valence electrons left, place them on the central element. Note: In some cases, the central element doesn't have enough electrons to make it a complete octet. In this case use the lone electron pairs on the outside elements to form double or triple bonds to connect the central element to the outside elements.

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