When building an atom, pay close attention to the particles' electrical charges. Protons have a charge of +1. Electrons have a charge of -1. Neutrons are neutral, as its name implies. A stable ...

Elements in the same horizontal row are in the same period. The periods are numbered from top to bottom. The period number is the same as the number of occupied electron shells.

called electron shells, around the nucleus. New evidence The discovery of electrons. Changes to the atomic model Atoms can be broken down into smaller parts. An atom is made of tiny negatively ...

This close to the atom, in order to not fall into it ... gaining effective relativistic mass, the two outermost electron shells (also drawn in towards the heavy nucleus) are slightly closer ...