A stable subatomic particle occurring in the atomic nucleus.  

An electron is - outside the nucleus and it has no mass . 

The act of changing something living or nonliving 

A subatomic particle of the same mass as a proton but without the electric charge . 

A system or standard of measurements  

consists of proton , electrons and neutrons 

no charge , 1AMU , inside the neucles 

Different mass and number on neutrons 

Where all the elements are located