Read your lecture notes, and, if necessary, cross check your notes with the Lecture Notes - a check up. Read each of the Quick Questions below and write down your answer. All atoms are the same. All atoms of the same element are the same. All atoms contain neutrons.
Electrons have less mass than either protons or neutrons.
In a neutral atom there are always equal numbers of protons and electrons. Isotopes are a family of atoms all of which have the same number of electrons. Electrons are found in clouds called orbitals surrounding the atomic centers. Electrons are sometimes exchanged between atoms. Ions are atoms that have gained or lost electrons.