1. Inside the Atom

Everything is made of atoms — and atoms are made of three smaller particles. Knowing their charges and locations unlocks most chemistry questions.

The three subatomic particles are:

• Protons — positive (+) charge, found in the nucleus (center).
• Neutrons — no charge (0), also in the nucleus.
• Electrons — negative (−) charge, moving around the nucleus in shells (energy levels).

The nucleus holds nearly all of the atom's mass (protons and neutrons are heavy; electrons are almost massless). In a neutral atom, the number of protons equals the number of electrons, so the positive and negative charges balance.

⚠️ Common misconception: an atom is mostly empty space — the tiny nucleus is surrounded by a relatively huge region where the light electrons move. (The neat circular orbits are a useful simplification, not a literal path.)

💡 Tip: protons +, neutrons 0, electrons −. Protons and neutrons are in the nucleus; electrons are outside it.