COH2 Lewis Structure, Characteristics: 13 Facts You Should Know


In this article, we shall learn about COH2 lewis structure, its solubility, polarity, uses and many other detailed explanations of COH2 which is known as formaldehyde.

COH2 is an organic compound known widely as formaldehyde, with its IUPAC nomenclature standing as Methanal. This pungent smelling gas is highly toxic that causes irritation to lungs when inhaled, eyes and skin.

However, COH2 lewis structure still is widely used for various reactions for preserving tissues, anti-infective agents, adhesives etc.

How to draw COH2 lewis structure ?

COH2 lewis structure is an electronic skeletal representation of a molecule that tells about the number of bonds, types of bonds, lone pairs, its resonance structure etc. This provides the skeletal structure adopted  by the respective molecular formula.

Molecular representation of COH2 from wikipedia

Methods to draw COH2 lewis structure :

  • Count the total number of valence electrons available from all the constituent atoms.
  • C has electronic configuration:  [He]2s22p2 , O electronic configuration : [He]2s22p4 and H electronic configuration : 1s1 . So a total of 12 valence electrons are available to construct the lewis dot structure.
  • Central atom with least electronegativity is chosen as the central atom. Electronegativity of C = 2.55, H = 2.2 and O = 3.44 . However, in this case and most organic compounds with carbon in it, C is chosen as the central atom as it can form four bonds due to its catenation property, while H can form only one bond pair, and oxygen can form only 2 bond pairs.
  • Each constituent atom will accommodate 8 electrons to fill their octet provided they are  not expanded valence shell atoms or electron deficient atoms with covalency less than 4.
  • A single bond is drawn from each atom with the valence electrons to the nearby atoms.
  • As there are only 3 atoms around the central atom, the octet of C and O can be completed only when a double bond is created between C and O . In doing so, 4 electrons are left which do not take part in bond formation and so they exist as lone pairs of electrons on O atoms.

Note: Electron deficient elements i.e., with covalency less than 3 or elements with covalency greater than 4 will violate octet rule as they have either less subshell or expanded subshell to accommodate electrons. Eg. H2 , SF6

Step by step construction of COH2  lewis structure :

coh2 lewis structure
COH2 Lewis dot structure formation.

COH2 lewis structure formal charge :

Formal charge tells about the electronic charge acquired by each constituent atom in  lewis dot structure.

Knowing formal charge of every atom, gives a clear and complete representation of the  molecule.

Generally, formal charge can be calculated mathematically by the formula :

Formal charge = (Number of valence electrons in a free atom of the element) – (Number of unshared electrons on the atom) – (Number of bonds to the atom)

In addition, Charge on the molecule= sum of all the formal charges.

Formal Charge of Ha ,Hb  = 1 – 0 – 1 = 0

Formal Charge of C = 4 – 0 – 4 = 0

Formal Charge of O = 6 – 4 – 2 = 0

Formal charge assigned to the constituent atoms.

COH2 lewis structure resonance :

COH2 lewis structure has 3 distinct resonance structures shown below.

The pi electrons can delocalize as they are less strongly held by atoms as compared to a sigma bonded electrons. More the number of resonance structures, greater is the resonance energy and more is its stability.

The first 3 resonance structures show how pi electrons delocalize over the C and O atoms making the double bond a partially double bond with single bond character as well.

Resonance structure showing electron delocalisation.

COH2 lewis structure octet rule :

COH2 lewis structure C and O follow the octet rule.

Each constituent atom has a complete octet, with H containing only 2 valence electrons in their outermost shell which being an exception for not having room/shells to accommodate electrons. Also its covalency is 2.

COH2 valence electrons :

Electronic configuration of C: [He]2s22p2

Electronic configuration of O: [He]2s22p4

Electronic configuration of H: 1s1

Carbon has 4 valence electrons, Oxygen has 6 valence electrons and Hydrogen has 1 valence electron. There are 2 H atoms so a total of 2 valence electrons contribution from H.

So, we have a total of 4+6+2 = 12 valence electrons. These 12 valence electrons constitute the complete octet of the COH2 lewis structure.

COH2 lewis structure has a total of 12 valence electrons.

COH2 lewis structure lone pairs :

There is 2 lone pairs of electrons residing on O atom. C has only bond pairs and H also has only bond pair of electrons.

COH2 lewis structure has 2 lone pairs of electrons residing on O atoms.

Lone pairs of electrons represented by 4 dots on O atom.

COH2 lewis structure hybridization :

Ground state electronic configuration of C: [He]2s22px12p1y2pz

Ground state electronic configuration of O: [He]2s22p2x2p1y2p1z

Ground state electronic configuration of H: 1s1

Excited state electronic configuration of C: [He]2s12px12p1y2p1z

C undergoes sp2 hybridization where its s, and 2 p hybrid orbitals containing one electron each pairs with 2 H and 1 O hybrid orbitals, the remaining one electron of 2pz hybrid orbital makes pi bond formation with one of the singly occupied p hybrid orbital of O. H undergoes sigma bond formation .

From the electronic configuration of O, it is clear that one of the singly occupied 2p orbitals forms sigma bond by overlapping with the sigma orbital of c along their internuclear axis.

The other singly occupied 2p orbital of O undergoes sidewise overlapping to form a pi bond as shown in the lewis structure diagram. The two non-hybridized s and one of the 2p prbitals containing paired electrons exist as lone pairs of electrons on O.

Overall, O has p2 hybridization, C has sp2 hybridisation.

COH2 lewis structure hybridisation along with the acquired shape- Trigonal planar

COH2 lewis structure shape :

From the above discussion of its hybridization, it adopts a trigonal planar structure with all the atoms being on plane and its shape is almost similar to that of an equilateral triangle.

The central atom is surrounded by 3 atoms in the periphery like that of an equilateral triangle. The atoms other that central atom is also called as peripheral atoms.

COH2 lewis structure angle :

COH2 adopts a trigonal planar shape with 1200 bond angle which is well justified as it is a sp2 hybridized molecule.

Is COH2 lewis structure polar or nonpolar ?

COH2 lewis structure is a polar molecule. It can be explained on the basis of their electronegativity difference which in this case has O atom the highest electronegativity. O, with X = 3.44, highest pulls the electron density of C towards itself which in turn pulls the electron density of H towards C making H partially positive.

This makes C slightly positively charged and O gaining partial negative charge which creates charge separation between the two ends of the molecule. This results in dipole formation which is responsible for the polar nature of the formaldehyde molecule.

X= Stands for electronegativity magnitude

Arrow indicates dipole moment vector.

Is COH2 lewis structure ionic ?

COH2 lewis structure is ionic in nature.

As O has greater electronegativity O = 3.44 , it pulls the electron density of C which has electronegativity of C = 2.55 towards itself which in turn pulls the electron density of H [H = 2.22]  towards C making H partially positive.

This makes C slightly positively charged and O gaining partial negative charge which creates charge separation between the two ends of the molecule making the molecule ionic.

COH2 lewis structure solubility :

Due to its polar nature, it is completely soluble in water and slightly soluble in polar solvents like acetone, ether, ethanol.

  • Water – completely soluble
  • Acetone – soluble
  • Ether – Partially soluble
  • Chloroform – Immiscible

Is COH2 lewis structure symmetrical or asymmetrical ?

COH2 lewis structure is a symmetrical molecule. When a mirror plane is passed through C=O bond, it produces identical mirror image where both the H when observed cannot be distinguished from one another.

Its point group is C2v similar to that of a H2O molecule.

Is COH2 lewis structure acidic or basic ?

COH2 lewis structure is a very weak acid. It acts more acidic when present in solid polymer forms. In gaseous state, it is quite basic in nature.

Conclusion :

COH2 lewis structure is a symmetrical trigonal molecule which has been widely used as formalin in biological systems and medical fields.

Nandita Biswas

Hello. I am doing my Masters in Chemistry with a specialization in organic and physical chemistry. Also, I have done two projects in chemistry- One dealing with colorimetric estimation and determination of ions in solutions. Others in Solvatochromism study of fluorophores and their uses in the field of chemistry alongside their stacking properties on emission. I have also specialized in Resin chemicals. Let's connect through LinkedIn-https://www.linkedin.com/in/nandita-biswas-244b4b179

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