# Why, in terms of atoms, are CH_3CH_2OH and CH_3CHO not isomers of each other?

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."

$C {H}_{3} C {H}_{2} O H$ has one more $O$ and $H$ than $C {H}_{3} C H O$

An example of an isomer is ${C}_{4} {H}_{8}$, as shown in this picture

It has the same amount of C and H atoms, but they're just arranged differently.