Why, in terms of atoms, are CH3CH2OH and CH3CHO not isomers of each other?

1 Answer

Because they don't follow the definition of an isomer

Explanation:

Here is the Oxford Dictionary definition of an isomer
"Each of two or more compounds with the same formula but a different arrangement of atoms in the molecule and different properties."

CH3CH2OH has one more O and H than CH3CHO

An example of an isomer is C4H8, as shown in this picture
![www.chemguide.co.uk
It has the same amount of C and H atoms, but they're just arranged differently.