Ions

Naturally, atoms are electrically neutral because negatively charged electrons neutralizes the positively charged protons as they both present in equal numbers. However, an atom can become positively or negatively charged if it gains or loses electrons.

        When an atom gives up an electron, it becomes positively charged and is called a positive ion. When it gains an electron it becomes negatively charged and is called a negative ion.

        Electrons in the outermost shell of an atom are loosely tied to nucleus and are free to move from one atom to another. This movement happens randomly, but by applying external force (a battery or DC generator), they can be made to move in one direction. This flow of electrons from one atom to another in one direction is called electrical current.