Why is the electron the part of the atom that moves when an electric current flows?

Question

Why is the electron the part of the atom that moves when an electric current flows?

Answer 1

The electron is the part of the atom that forms bonds with other atoms.  The protons and neutrons stay in place, and the electrons from one atom join with the electrons in another atom in forming bonds.  The protons and neutrons are the stationary part of the atomic matrix because they are much much heavier than the electrons.  They're like bowling balls and electrons are like flies buzzing around them.  

In certain materials, such as metals, electrons bond in the substance so that they form one giant fuzzy orbital throughout the entire substance almost like one gigantic molecule.  When a charge is applied, the electrons are free to move across the entire orbital.  In other substances, the electrons are just shared within one molecule, but they can't move to the next molecule.  In this case, they can't move when a charge is applied--these are nonmetals and other insulators, such as glass, rubber, etc.

Answer 2

The electron is the outer part of an atom and it has a negative charge. Although the protons in the nucleus has a positive charge, there's also neutrons which have no charge. This makes it difficult to carry an electric current.

Therefore only the Electrons can cause and electric current to flow.