Atoms and isotopes

The idea

Atoms are very small, with a radius of about 1 × 10⁻¹⁰ m. The nucleus contains protons and neutrons and is less than 1/10 000 of the atom's radius; most of the mass is in the nucleus. Electrons are arranged at different distances from the nucleus and can move to higher levels by absorbing electromagnetic radiation, or lower levels by emitting it. Isotopes of an element have the same number of protons but different numbers of neutrons. Atoms that lose or gain outer electrons become ions.

1. Protons = atomic number.
2. Neutrons = mass number − atomic number.
3. Isotopes: same protons, different neutrons.

Watch out Isotopes have the same chemical properties because they have the same number of electrons.