So you have seen the above image by now, right?
Let me explain the above image in short.
CH4 lewis structure has a Carbon atom (C) at the center which is surrounded by four Hydrogen atoms (H). There are 4 single bonds between the Carbon atom (C) and each Hydrogen atom (H).
If you haven’t understood anything from the above image of CH4 lewis structure, then just stick with me and you will get the detailed step by step explanation on drawing a lewis structure of CH4.
So let’s move to the steps of drawing the lewis structure of CH4.
Steps of drawing CH4 lewis structure
Step 1: Find the total valence electrons in CH4 molecule
In order to find the total valence electrons in CH4 molecule, first of all you should know the valence electrons present in carbon atom as well as hydrogen atom.
(Valence electrons are the electrons that are present in the outermost orbit of any atom.)
Here, I’ll tell you how you can easily find the valence electrons of carbon as well as hydrogen using a periodic table.
Total valence electrons in CH4 molecule
→ Valence electrons given by carbon atom:
Carbon is group 14 element on the periodic table.  Hence the valence electrons present in carbon is 4.
You can see the 4 valence electrons present in the carbon atom as shown in the above image.
→ Valence electrons given by hydrogen atom:
Hydrogen is group 1 element on the periodic table.  Hence the valence electron present in hydrogen is 1.
You can see that only 1 valence electron is present in the hydrogen atom as shown in the above image.
Total valence electrons in CH4 molecule = valence electrons given by 1 carbon atom + valence electrons given by 4 hydrogen atoms = 4 + 1(4) = 8.
Step 2: Select the central atom
For selecting the center atom, you have to remember that the atom which is less electronegative remains at the center.
(Remember: If hydrogen is present in the given molecule, then always put hydrogen outside.)
Now here the given molecule is CH4 (methane) and it contains carbon atom (C) and hydrogen atoms (H).
You can see the electronegativity values of carbon atom (C) and hydrogen atom (H) in the above periodic table.
If we compare the electronegativity values of carbon (C) and hydrogen (H) then the hydrogen atom is less electronegative. But as per the rule we have to keep hydrogen outside.
So here the carbon atom (C) is the center atom and the hydrogen atoms (H) are the outside atoms.
Step 3: Connect each atoms by putting an electron pair between them
Now in the CH4 molecule, you have to put the electron pairs between the carbon atom (C) and hydrogen atoms (H).
This indicates that the carbon (C) and hydrogen (H) are chemically bonded with each other in a CH4 molecule.
Step 4: Make the outer atoms stable
Now in this step, you have to check the stability of the outer atoms.
Here in the sketch of CH4 molecule, you can see that the outer atoms are hydrogen atoms.
These outer hydrogen atoms are forming a duplet and hence they are stable.
Also, in step 1 we have calculated the total number of valence electrons present in the CH4 molecule.
The CH4 molecule has a total 8 valence electrons and all these valence electrons are used in the above sketch of CH4.
Hence there are no remaining electron pairs to be kept on the central atom.
So now let’s proceed to the next step.
Step 5: Check the octet on the central atom
In this step, you have to check whether the central carbon atom (C) is stable or not.
In order to check the stability of the central carbon (C) atom, we have to check whether it is forming an octet or not.
You can see from the above picture that the carbon atom is forming an octet. That means it has 8 electrons.
And hence the central carbon atom is stable.
Now let’s proceed to the final step to check whether the lewis structure of CH4 is stable or not.
Step 6: Check the stability of lewis structure
Now you have come to the final step in which you have to check the stability of lewis structure of CH4.
The stability of lewis structure can be checked by using a concept of formal charge.
In short, now you have to find the formal charge on carbon (C) atom as well as hydrogen (H) atoms present in the CH4 molecule.
For calculating the formal charge, you have to use the following formula;
Formal charge = Valence electrons – (Bonding electrons)/2 – Nonbonding electrons
You can see the number of bonding electrons and nonbonding electrons for each atom of CH4 molecule in the image given below.
For Carbon (C) atom:
Valence electrons = 4 (because carbon is in group 14)
Bonding electrons = 8
Nonbonding electrons = 0
For Hydrogen (H) atom:
Valence electron = 1 (because hydrogen is in group 1)
Bonding electrons = 2
Nonbonding electrons = 0
|Formal charge||=||Valence electrons||–||(Bonding electrons)/2||–||Nonbonding electrons|
From the above calculations of formal charge, you can see that the carbon (C) atom as well as hydrogen (H) atom has a “zero” formal charge.
This indicates that the above lewis structure of CH4 is stable and there is no further change in the above structure of CH4.
In the above lewis dot structure of CH4, you can also represent each bonding electron pair (:) as a single bond (|). By doing so, you will get the following lewis structure of CH4.
I hope you have completely understood all the above steps.
For more practice and better understanding, you can try other lewis structures listed below.
Try (or at least See) these lewis structures for better understanding: