A Lewis structure shows only VALENCE electrons. The first step to drawing a Lewis structure is to figure out how many valence electrons each element in the compound has. Once you have figured out valence electrons for each element, add the numbers together to get the total valence electrons for the compound. The correct structure will have the exact same number of electrons as the total number of valence electrons.
Once you know how many electrons you need, you can start arranging the atoms. The central atom is the element with the lowest electronegativity. If carbon is present it is the central atom. Hydrogen and halogen atoms are usually at the end(s) of the molecule.
Now that you have the skeleton, position electrons around the atoms so that they satisfy the octet rule. Most atoms will have 8 electrons and hydrogen will have 2. A dot represents a single electron and a dash represents two electrons. A single dash is a single bond, two dashes is a double bond, and three dashes is a triple bond. Always start with single bond and if you have used too many electrons, go back and change single bonds to double/triple bonds where necessary.
Double check your structure. Make sure that the total number of electrons you added equals the total number of valence electrons you are supposed to have.
In a Lewis structure, the three basic elements are:
- the symbol of the atom;
- the chemical bonds, which are represented by lines;
- dots around the symbol of the element, which represent the unbonded electrons.
The first step in drawing a Lewis structure is to establish which is the element whose symbol will be drawn central. The decision will be made based on the lowest electronegativity of elements, this characteristic being established with the help of periodic table. After selecting the atom,it's symbol will be wtitten and after that it will be drawn the chemical bond with the other atoms. It's is important that the central atom it will have a single chemical bond, namely a single line.
Also you have to take into consideration the octet rule that claims that an atom is stable if it has on the outer shell, 8 electrons.
It's important to establish how many electrons has an atom around it, after that, drawing of these electrons as dots, being an easy task.
Also, do not forget that a bond means a pair of electrons.
After Lewis structure has been completed, finish the drawing operation by placing it between brackets.
It is very simple. Just draw the chemical symbol of the element that is represented in the periodic table and draw the valence electrons on the top, bottom, left and right of the letter to show the amount of it it consists of.