What Is Electricity? (2013)

This force is part of the “glue” that holds atoms together, but it’s also the tool we need to make electrons (and charges) flow! Using enough electrostatic force on the valence electron–either pushing it with another negative charge or attracting it with a positive charge–we can eject the electron from orbit around the atom creating a free electron. In this chaos the free electron eventually finds a new atom to latch on to; in doing so, the negative charge of that electron ejects another valence electron from the atom.

Source: learn.sparkfun.com