C8H18 (octane) has eight carbon atoms and eighteen hydrogen atoms.
In C8H18 Lewis structure, there are seven single bonds between the eight carbon atoms. The first carbon and last carbon are attached with one carbon and three hydrogen atoms, and the remaining six carbons are attached with two hydrogen atoms. And none of the atoms has a lone pair.
Alternative method: Lewis structure of C8H18
Rough sketch
- First, determine the total number of valence electrons
In the periodic table, carbon lies in group 14, and hydrogen lies in group 1.
Hence, carbon has four valence electrons and hydrogen has one valence electron.
Since C8H18 has eight carbon atoms and eighteen hydrogen atoms, so…
Valence electrons of eight carbon atoms = 4 × 8 = 32
Valence electrons of eighteen hydrogen atoms = 1 × 18 = 18
And the total valence electrons = 32 + 18 = 50
Learn how to find: Carbon valence electrons and Hydrogen valence electrons
- Second, find the total electron pairs
We have a total of 50 valence electrons. And when we divide this value by two, we get the value of total electron pairs.
Total electron pairs = total valence electrons ÷ 2
So the total electron pairs = 50 ÷ 2 = 25
- Third, determine the central atom
Here hydrogen can not be the central atom. Because the central atom is bonded with at least two other atoms, and hydrogen has only one electron in its last shell, so it can not make more than one bond.
Now there are eight atoms remaining and all eight atoms are carbon, so we can assume any one as the central atom.
Let’s assume that the central atom is first carbon.
Therefore, place carbons in the center and hydrogens on either side.
- And finally, draw the rough sketch
Lone pair
Here, we have a total of 25 electron pairs. And twenty-five bonds are already marked. So we do not have to mark any electron pair as a lone pair on the sketch.
Final structure
The final structure of C8H18 consists of a chain of eight carbon atoms linked by single covalent bonds, with hydrogen atoms attached to satisfy the remaining bonding sites. In this arrangement, the six internal carbon atoms are each bonded to two other carbons and two hydrogens, while the two terminal carbon atoms are bonded to one carbon and three hydrogens. Within this configuration, every carbon atom satisfies the octet rule by forming four bonds, and every hydrogen atom reaches its stable duet state through its single shared bond. This setup is the most stable because it results in formal charges of zero for every atom, representing the most energetically favorable state for the molecule. Thus, this specific electronic distribution serves as the definitive and most accurate Lewis representation of octane.
Next: P2H4 Lewis structure
External video
- How to Draw the Lewis Dot Structure for C8H18: Octane – YouTube • Wayne Breslyn
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