Find out how to draw the lewis dot structure of a molecule in a simple way with this step by step guide

1. How to write the Lewis structure
of a molecule
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2. Steps to write the Lewis structure of a
molecule
1. Find the number of valence electrons for
each of the atoms in the molecule.
The number of valence electrons is usually the
same as the group number where the element
is located.

3. The number of valence electrons for alkaline metals is 1
(group 1)

4. The number of valence electrons for alkalineearth metals is 2
(group 2)

5. The number of valence electrons for group 3 elements is 3

6. The number of valence electrons for group 4 elements is 4

7. The number of valence electrons for group 5 elements is 5

8. The number of valence electrons for group 6 elements is 6

9. The number of valence electrons for group 7 elements is 7

10. Example: methane
• Methane: CH4
• C is located in group 4, thus possess 4 valence
electrons
• H is located in group 1, thus possess 1 valence
electron

11. 2. Count the total number of valence electrons
in the molecule:
Sum the valence electrons from each atom in
the molecule

12. For methane CH4
• Total valence e. from C: 4
4 e. x 1 C = 4
• Total valence e. from H: 4
1 e. x 4H = 4
Total valence e. in the molecule: 4 + 4 = 8

13. 3. Use the octet rule to figure how many octet
electrons the atoms should have:
Most atoms need 8 electrons to complete their
valence shield
Hydrogen is an exception and needs only 2

14. For methane CH4
• Carbon should have 8 valence electrons
• Each hydrogen should have 2 valence
electrons

15. 4. Draw an initial sketch of the molecule by
placing the symbol of each atom in a diagram
For methane:
H
H C H
H

16. 5. Place the valence electrons of each
atom around them, starting from the
outer atoms

17. For methane CH4
• Hydrogen has 1 valence electron:

18. For methane CH4
• Carbon has 4 valence electrons:

19. 6. Each bond in a molecule is made up from
two electrons.
Each atom in the molecule need to be bonded
together to its nearest atom .

20. For methane CH4
• Form single bonds between the atoms:

21. For methane CH4
• Form single bonds between the atoms:

22. For methane CH4
• Form single bonds between the atoms:

23. For methane CH4
• Form single bonds between the atoms:

24. For methane CH4
Now the structure is complete:

25. 7. At the end, each atom should be surrounded
by eight electrons (following the octet rule)
Remember that H only needs 2 electrons

26. For methane CH4
• Carbon is surrounded by 8 electrons

27. For methane CH4
• Each hydrogen is surrounded by 2 electrons

28. Remember these simple rules when drawing
Lewis structures:
• Hydrogen and the halogens form single bonds
• The oxygen family forms single or double
bonds. They need at least 2 bonds.
• The nitrogen family forms single, double or
triple bonds. They need at least 3 bonds.
• The carbon family needs 4 bonds.

29. Practice writing the Lewis structure of any
molecule!
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