Explain your understanding of functional group in organic chemistry

A functional group in organic chemistry is an atom or group of atoms that is responsible for the specific properties of an organic compound. Some examples of functional groups include alcohols, alkyl halides, ethers, aldehydes, ketones, amines, carboxylic acids, and esters.

Functional groups also play an important part in organic compound nomenclature; combining the names of the functional groups with the names of the parent organic compounds provides a way to distinguish compounds.

The atoms of a functional group are linked together and to the rest of the compound by covalent bonds. The first carbon atom that attaches to the functional group is referred to as the alpha carbon; the second, the beta carbon; the third, the gamma carbon, etc. Similarly, a functional group can be referred to as primary, secondary, or tertiary, depending on if it is attached to one, two, or three carbon atoms.  

let that person have a turn to speak : )

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)