An atom is neutral when it has an equal number of protons and electrons, so the total positive charge and total negative charge cancel out to give a net charge of zero.

What “neutral” means

  • Protons carry a positive electric charge and sit in the nucleus.
  • Electrons carry an equal-magnitude negative charge and move around the nucleus.
  • When the number of protons = number of electrons, the charges balance and the atom is neutral (overall charge 0).

Role of neutrons

  • Neutrons have no electric charge, so they do not affect whether the atom is neutral or charged.
  • Their main job is to add mass and help keep the nucleus stable , especially in heavier elements.

When atoms are not neutral

  • If an atom gains extra electrons, it has more negative than positive charge and becomes a negatively charged ion (anion).
  • If it loses electrons, it has more protons than electrons and becomes a positively charged ion (cation).

Simple way to picture it

  • Think of each proton as +1 and each electron as −1.
  • Neutral atom: +1 and −1 paired for every proton–electron pair, so the sum is 0.

TL;DR: What makes an atom neutral is having the same number of protons (positive) and electrons (negative), so their charges exactly cancel out and the net charge is zero.

Information gathered from public forums or data available on the internet and portrayed here.