Molecular geometry, hybridization and the MO diagram for H2CO

It is an aldehyde because of its molecular formula, which is H2CO. The functional group -HCO- is found in the molecules of aldehydes, the lowest of which being formaldehyde, which has a single carbon atom.

Because of its molecular structure and bonding, it exhibits unusual physical and chemical properties. This colourless, poisonous gas has an unpleasant and pungent scent that makes it difficult to breathe. Trimer (1,3,5-trioxane) or polymeric form is known as Paraformaldehyde in its solid state.

formalin is the most common form of formaldehyde storage. Because of its strong reactivity, this substance is a key component in synthetic chemistry.

The nature and structure of formaldehyde’s chemical bonds is one of the most important indications to its diversity in physical state and reactivity. The Lewis structure is an excellent place to start when trying to decipher their meaning.

the Lewis H2CO skeleton

The simplest way to depict a compound’s chemical formula is to use a Lewis structure representation, which shows the compound’s valence and bonding electrons along with the formal charge.

This diagram shows the dots that represent the lone pairs of electrons that make up each individual atom, while the lines connecting the two atoms that share the electron pair are depicted between them.

In a Lewis structure, the official charge must be included. If you want to know the formal charge of every atom in a molecule, you need to know the overall charge on it, which is written outside square brackets in the most complete structures.

Drawing the Lewis structure of Formaldehyde is easy if you know how

Calculate the total number of valence (or positive) atoms in the molecule by adding or subtracting the group number of each atom plus the total charge.

There are no negative or positive charges attached to formaldehyde.

AtomValence electrons
2 H2

Choosing the centre atom is step two. Single-bonding ability and/or ability to extend octet are usually the atom’s most important properties.

Carbon, in this instance, has the ability to make four bonds. Single bonds to the core atom are now used to connect the remaining terminal atoms.

When all of the terminal atoms’ octets have been filled with lone pairs, the remaining electrons are added as lone pairs to the remaining bonds to complete the octets.

The most negative components should be added first, followed by the lone pair of electrons.

Formaldehyde has six electrons, thus we have made three bonds with it. So there are just six electrons left, and all of them will be spent on Oxygen.”

The octet on the centre atom must now be completed. A terminal atom’s lone pair of electrons can be used to build another bond if no other electrons are available.

To complete the octet around carbon, we pull a lone pair from oxygen.

Step 5: The formal charge of each atom is now calculated.

Number of valence electrons minus 12 times the number of bonding electrons plus the number of lone pairs is the formula for calculating the formal charge.

Carbon has a formal charge of 0

O2’s formal charge is 0: 6 – 12*4 = 14

Hydrogen: Formal charge = 1 – ½*2 – 0 = 0

As a result, the final Lewis structure is as follows:

Hybridization of H2CO

Lewis structure of H2CO provides a fundamental image of bonding, but we still don’t know the molecule’s shape. Covalent bonds have a definite spatial layout and are hence referred to as directional bonds.

The atomic orbitals of the central atom can be used to study the nature of these covalent bonds through the use of hybridization.

Let’s look at carbon as an example of formaldehyde. The electrical ground state structure of carbon is 1s2 2s2 2p2.

A carbon atom that is unhybridized can only form two single bonds along the internuclear axis (commonly referred to as the z-axis). Formaldehyde, on the other hand, has three single bonds, thus hybridization is critical.

With an angle of 1200, the sp2 hybrid orbitals are planar Carbon’s 2p orbital is perpendicular to the molecular plane. In order to make a bond with oxygen’s 2p orbital, it is used for sideways overlap.

While oxygen is in the same orbital as the other lone pair electrons in this molecule, it forms just one sp2 hybrid bond since the other two orbitals have been filled. In the next section, we’ll look at why the bond angles aren’t exactly 1200 degrees.

The formula can also be used to figure out how much a molecule will hybridise.

12 * (H+V+A+C), where X = (H+V+A) – C.

Valence electrons in the core atom are referred to as “V.”

Number of atoms at the monovalent end of the ring

The cationic charge is denoted by the letter C.

Anionic charge is denoted by the symbol A.

If X is more than 1, then the number of hybrid orbitals is

3 is the formula for formaldehyde X = 12 * (2+4+1+4+1+0+0) One s and two p orbitals can be combined to generate sp2 hybrids, which are three hybrid orbitals.

Chemistry of H2CO’s Molecular Structure

The Valence Shell Electron Repulsion Theory aims to predict the shape of individual molecules using the principle of minimal energy and maximum stability as a guideline.

For the most stable geometries, minimization of repulsion between electron pairs surrounding the centre atom is required to attain the lowest possible energy level according to VSEPR.

Our focus in formaldehyde is on the electron pairs surrounding Carbon. We require the steric number of Carbon, which is the number of atoms linked to the centre atom, as well as the number of lone pair electrons on the central atom in order to apply VSEPR to the system.. Carbon has a count of three.

The molecular shape is trigonal planar if the total number of domains (steric no.) is 3 and the lone pair is 0.

Repulsion’s amplitude increases in the following order:

Lone pair- Lone pair

To compensate for this distortion, the carbon-oxygen double bond has a higher repulsion than the carbon-hydrogen single bond. The O-C-H and H-C-H bond angles are near to or above 1200 degrees.

Anatomy of the H2CO Molecular Orbital

Hybrid orbitals and VSEPR theory have already explored a large number of structural characteristics of the formaldehyde molecule. The molecular orbital theory (MOT) is the most in-depth description of chemical bonding based on quantum mechanical features.

Similar to atomic orbitals, molecular orbital theory (MOT) describes electron density and dispersion in molecules. Molecular orbitals are filled up in the same way as they are in atomic orbitals, and the total number of molecular orbitals generated is equal to the total number of atomic orbitals that have been combined.

With bonded molecular orbitals having lower energies, the Y axis of the molecular orbital diagram depicts energy. The electron density between the two nuclei, when attraction triumphs over repulsion, is represented by a bonding molecular orbital.

Repulsion is greater than attraction in an anti-bonding orbital, therefore no bond is established between the two nuclei. Atomic orbitals known as non-bonding orbitals are those that remain confined to a single atom and do not participate in the creation of bonds.

Formaldehyde is an example of a compound in which a linear combination of atomic orbitals (LCAO) approximation method is applied.

By using molecular orbital theory, we may predict molecular spectra, electrostatic potential maps, excited state features, and molecular reactivity.


For the H2CO molecule, in this post, we have studied how to sketch the lewis structure of the molecule and how VSEPR theory and molecular orbital theory may be used to create molecular geometry.

Feel free to leave any questions or comments below if you have any. I eagerly await your thoughts.

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Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.


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