Formaldehyde (CH2O) is a colourless gas,it is the most common and basic aldehyde, composed of two hydrogens, one carbon and one oxygen.

Structure

Carbon has four valence electrons, three of which are sp2 hybridised, resulting in two C – H and one C – O bond. The fourth carbon electron remains unhybridized, forming a “bond (Pi bond)” with an oxygen electron. This arrangement results in H2C=O. Carbon and oxygen have a double bond, which consists of one pi-bond and one sigma-bond. The sigma bond is stronger than the pi bond.

Formaldehyde (methanal) has a “trigonal planar” structure and a bond angle of 120° according to Valence Shell Electron Repulsion Theory (VSEPR).

Is Formaldehyde Polar or Nonpolar?

The difference in electronegativity and electron sharing between two atoms in a covalent bond determines whether the molecule is polar or non-polar.

When the sharing of electrons between two atoms is unequal, the molecule is said to be polar, and when the sharing of electrons between the atoms is equal, the molecule is said to be non-polar.

Formaldehyde (CH2O) is a polar compound. This is because of the unbalanced electron density. The electronegativity difference between hydrogen and carbon is negligible, whereas the electronegativity difference between carbon and oxygen is large enough to cause polarity.

This means that electrons in the double bond are more attracted to oxygen, causing charges to shift, resulting in a partial positive charge on the carbon and a partial negative charge on the oxygen.

The difference in electronegativity allows polarity to make a molecule non-symmetrical (asymmetrical), allowing the -ve charge to be centralised on one side of the molecule by the oxygen.