Each element is made up of one kind of atom. We can define an atom as the smallest part of an element that can enter into combination with other elements. Because of its single proton, the atom of hydrogen is assigned an atomic number of 1 . The charge of the electron is the same magnitude as that of the proton, so the atom as a whole is electrically neutral. Its proton accounts for almost all the weight of the atom.
Neutrons have the same weight as protons but no electrical charge.
The helium atom has two electrons so that, once again, the atom as a whole is neutral. The structure of each of the other kinds of atoms follows the same plan. There are no gaps in the list. Each element has a unique atomic number and its atoms have one more proton and one more electron than the atoms of the element that precedes it in the list. Electrons Electrons are confined to relatively discrete regions around the nucleus.