Formaldehyde (IUPAC name: methanol) is the simplest among the aldehydes. Its chemical formula is CH2O, its number CAS is 50-00-0. In  a water solution of 37% is marketable known as formalin. The molecule is composed by a carbon atom (hybridization sp2) in the middle of a triangle almost equilateral with two hydrogen atoms and an oxigen one at the vertex. Formaldehyde is at a gaseous state at room temperature, but you can find it usually in other states: as water solution at 37% or as paraformaldehyde (IUPAC name: 1,3,5-trioxan), cyclic molecule formed by the union of three molecules of Formaldehyde.