Formaldehyde is an organic compound with the chemical formula CH2O that appears as a colourless gas. It is the most common and simplest aldehyde, consisting of two hydrogens, one carbon and one oxygen.
Lewis structure diagrams show how many valence electrons are available within an atom and participate in bond formation. It also enables visualising the behaviour of the valence electrons within the molecule and determining whether or not a lone pair of electrons exist.
The structure is made up of electrons drawn as dots, mostly in pairs, around the atom symbol.
Table of Contents
- How to draw Lewis Structure for CH2O
- Molecular Geometry of CH2O
- Hybridization of CH2O
- Polarity of CH2O
- Frequently Asked Questions – FAQs
How to draw Lewis Structure of CH2O
The below-given steps are to be followed while drawing the lewis structure of CH2O
1. Determine the total number of electrons in the carbon, hydrogen, and oxygen valence shells.
In the periodic table-
Hydrogen is a Group IA element with only one electron in its last shell. Oxygen is a Group VIA element with six electrons in its last shell. Carbon is a Group IVA element with four electrons in its last shell.
- The total number of valence electrons in carbon is four.
- The total number of valence electrons in oxygen is six.
- The total number of valence electrons in hydrogen is one.
Total valence electrons available for drawing the Lewis structure of CH2O = 4 + 1(2) + 6 = 12 valence electrons.
2. Determine the total number of electron pairs that exist as lone pairs and bonds.
Total valence electron pairs = σ bonds + π bonds + lone pairs at valence shells.
Total electron pairs are calculated by dividing the total valence electron count by two. In the valence shells of the HCHO molecule, there are 6 pairs of electrons.
3. Choosing the central atom
Carbon is more electropositive than oxygen. Therefore, it will be the central atom.
4. Mark atoms with lone pairs.
A total of six electron pairs should be present as lone pairs and bonds in valence shells.
- There are already three bonds. As a result, there are three more lone pairs to mark on hydrogen, carbon, and oxygen atoms.
- First, mark any remaining lone pairs on the outside atoms. We can’t mark lone pairs on hydrogen atoms because there are already two electrons in the valence shell. As a result, the remaining three lone pairs on the oxygen atom should be marked. As a result, all three remaining electron pairs are marked, and there are no more valence electron pairs to mark on the carbon atom as lone pairs.
5. If there are charges on atoms, mark them.
The charges on the oxygen atom and the central carbon atom are as follows.
6. To obtain the best Lewis structure minimise charges on atoms by converting lone pairs to bonds.
There are charges on the carbon and oxygen atoms in the centre. We will convert a single covalent bond from a single lone pair of oxygen atoms.
7. Check the stability of each atom
It can be checked by using the formula-
Formal charge = Valence Electrons – Unbonded Electrons – ½ Bonded Electrons
| Elements | Carbon | Oxygen | Hydrogen |
|---|---|---|---|
| Formula Applied | Valence electrons= 4
Lone pair electrons= 0 Shared pair electrons (two single bond and one double bond) = 8 |
Valence electrons = 6
Lone pair electrons = 4 Shared pair electrons (1 double bond) = 4 |
Valence electrons = 1
Lone pair electrons = 0 Shared pair electrons (1 single bond) = 2 |
| Formal Charge | (4 – 0 – 8/2) = 0 | (6 – 4 – 4/2) = 0 | (1 – 0 – 2/2) = 0 |
Since the overall formal charge is zero, the above Lewis structure of CH2O is most appropriate, reliable, and stable in nature.
Molecular Geometry of CH2O
The molecular geometry of CH2O is trigonal planar because the central carbon atom has no lone pair and is attached to the two hydrogen atoms and one oxygen atom through two single bonds and one double bond.
Hybridization of CH2O
Total hybrid orbitals of CH2O = (the number of bonded atoms attached to carbon + the number of lone pairs on carbon atoms).
The carbon central atom is bonded with two hydrogen atoms and one oxygen atom in the Lewis structure of CH2O, and there are no lone pairs.
∴ Total hybrid orbitals = (3 + 0) = 3 which are only formed in the case of sp2 hybridization.
Polarity of CH2O
There is a difference in electronegativity values between carbon and oxygen, which causes charge imbalance and generates some dipole moment in the molecule, making CH2O a polar molecule.
Frequently Asked Questions on Lewis Structure of CH2O
Explain the formation of double bond In the CH2O Lewis structure.
Carbon requires 8 electrons in its outer shell to complete the octet and achieve stability, therefore we converted one lone pair of oxygen atoms to a single covalent bond. As a result, in nature, the bond formed between carbon and oxygen in the CH2O Lewis structure is a double covalent bond.
How many shared pair or lone pair electrons are present in the CH2O lewis structure?
The Lewis structure CH2O contains two lone pairs and four bonded pairs (two single bonds and one double bond).
What is the total number of valence electrons available for drawing the lewis structure of formaldehyde?
The total number of valence electrons available for drawing the lewis structure of formaldehyde is 12.
What is the molecular geometry of CH2O?
According to the VSEPR theory, the molecular geometry of CH2O is trigonal planar.
Why cannot Hydrogen be kept as the central metal atom in the lewis structure of CH2O?
Hydrogen atoms can only form one bond, therefore, they cannot be the central atom.
Comments