Both CH3 and C2H5 are chemical fragments called alkyl groups. They are not complete molecules on their own, but rather parts of larger molecules. Here's a breakdown:

CH3:

* Name: Methyl group

* Structure: One carbon atom bonded to three hydrogen atoms.

* Commonly found in: Methane (CH4), Methanol (CH3OH), and many organic compounds.

C2H5:

* Name: Ethyl group

* Structure: Two carbon atoms bonded to each other, with each carbon atom having three hydrogen atoms attached.

* Commonly found in: Ethane (C2H6), Ethanol (C2H5OH), and many organic compounds.

Key Points:

* These are not molecules themselves, but functional groups within larger molecules.

* The "R" in organic chemistry often represents an alkyl group like methyl or ethyl.

Let me know if you'd like to know more about specific compounds containing these groups!