Lewis dot structure gives an idea about outer most orbit electrons of an atom. This article is discussing about the Acetone lewis structure and explanations.
Acetone Lewis structure is written with the atomic symbol of atoms in the molecule. The outer orbit electrons of a particular atom are shown by dot symbols around that particular atom.
These electrons may forms bond with the outer shell electrons of the atom next to it. Or some of these electrons don’t take part in bond formation, remains as nonbonding electrons.
Structural formula of Acetone molecule
Acetone is a molecule in Carbonyl family. It is a smallest ketone molecule with molecular formula C3H6O or (CH3)2CO. So an acetone molecule contains three Carbon atoms, six hydrogen atoms and one oxygen atom.
Acetone lewis structure drawing
To draw the lewis structure of Acetone, all the outer orbit electrons of these atoms are first calculated. Carbon is an element of ‘group 14’, Oxygen is an element of ‘group 16’ and Hydrogen is a ‘group 1’ element in Periodic table.
Outer orbit electron calculation
Electronic configuration of a Carbon atom: 1s2 2s2 2p2. Electronic configuration of an Oxygen atom: 1s2 2s2 2p4. Electronic configuration of a Hydrogen atom: 1s1.
Hence the number of outer most shell electron in a Carbon atom is four. That of an Oxygen atom is six and for a Hydrogen atom is one.
In the Acetone molecule the total outer shell electrons for three Carbon atoms are (4×3) = 12. For six Hydrogen atoms these electron number will be (1×6) = 6. For that one Oxygen atom the total outer most shell electron number will be (6×1) = 6.
Thus in a Acetone molecule the number of total electrons in the outer orbit of the atoms are 24.
Number of electron pair calculation
In a bond forming between two atoms next to each other, there two electrons (a pair of electron) are involved.
We can find how many pairs of electrons participate in the bonding in Acetone molecule by dividing the number 24 by 2 and the number will be 12. As there are 24 outer orbit electrons in an Acetone molecule.
Total electron pairs which participate in molecule formation= total outer shell electrons in the molecule ÷ 2.
Arrangement of atoms in Acetone lewis structure
In Acetone lewis structure, the arrangement of atoms occurs in a way that generally the atom with less electronegative character will be the central atom in a molecule.
Here Hydrogen is the less electronegative atom. To be the central atom, at least it has to connect with two other atoms. Hydrogen has only one electron, so it can’t be the central atom.
Carbon becomes the central atom in the Acetone molecule. Hydrogen and Oxygen atoms are placed around the Carbon atoms. The bonding pair electrons are shown with straight lines between two atoms.
For now in the lewis structure, total eighteen electrons (nine pairs of electrons) are involved in bond formation.
As Hydrogen is a ‘group 1’ element it has no vacant orbital for the nonbonding electrons. Three unshared pairs of electrons are written over the Oxygen atom of the molecule.
Formal charge calculation
Now the formal charges of the atoms of Acetone have to calculate to properly distribute the electrons among the atoms.
Formal charge of a atom in a molecule = (outer shell electrons – nonbonding electrons – (1/2×bonding electrons))
The formal charge of the Carbon atom, attached with Hydrogen atoms = (4 – 0 – (1/2×8)) = 0.
The formal charge for the Carbon atom, attached with the Oxygen atom = (4 – 0 – (1/2×6)) = +1.
The formal charge of the Hydrogen atom = (1- 0 – (1/2×2)) = 0.
The formal charge of the Oxygen atom = (6 – 6 – (1/2×2)) = -1.
Stability consideration with formal charge
The structure is not a stable one as both the Oxygen and the central Carbon atom has formal charges.
To obtain a stable Acetone molecule structure the charges have to neutralize. This can be made by converting the unshared electrons into bond formation between the Oxygen atom and the central Carbon atom.
Final Acetone lewis structure
In the Acetone lewis structure there forms a pi bond (double bond) between the central Carbon atom and the Oxygen atom. Beside this the molecule has nine sigma bonds ( single bond).
The Oxygen atom of Acetone molecule has four unshared electrons. These electrons are written as pair of dot sign over the Oxygen atom.
Now if we count the outer shell electrons of each atom in the Acetone lewis structure, we found that every outer orbit of the atoms is full filled with electrons. This is the main condition for a stable configuration according to the Octet rule.