Question

What word or two-word phrase describes the shape of the formaldehyde ($C{{H}_{2}}O$) molecule?

Answer 1

Formaldehyde is a compound having a carbonyl group ($>C=O$) as a functional group. The carbon atom is a tetravalent atom, so it can form four covalent bonds, so the atoms attached in the formaldehyde will decide the shape.

Complete answer:
The shape of any molecule depends on the number and type of atoms attached to the central carbon atom.
Mostly if there are only two atoms in the molecule then it will be a linear structure, if three atoms are present on the central atom then it will be trigonal planar, if four atoms are present on the central atom then the structure will be tetrahedral or square planar, etc.
The given compound in the question is formaldehyde whose formula is $C{{H}_{2}}O$. The carbon atom will be the central atom in the molecule. The carbon atom is a tetravalent atom so, it can form four covalent bonds, so the atoms attached in the formaldehyde will decide the shape.
So, there is one oxygen atom and two hydrogen atoms attached to it. We know that an oxygen atom needs only two electrons to complete its octet, so it will form a double bond with the carbon atom. Each hydrogen atom will form a single bond with the carbon atom. So, the shape of the formaldehyde molecule will be trigonal planar. The structure is given below:

Note:
Don't get confused that all the bonds are present around the carbon atom so, its shape should be tetrahedral because a double bond is formed by oxygen which will decrease one position of the substituent.