The model further reveals information about the arrangement of electrons within the energy levels. Within the first energy level closest to the nucleus, two electrons can be located. In the second energy level, up to eight electrons can be found. The third level can hold up to eighteen electrons, and the fourth can hold up to thirty-two. The atomic orbitals are more complicated than this description implies, but this offers a glimpse at their arrangement.
All atoms follow the basic arrangement, yet atoms of different substances are different.
Scientists currently know of approximately 118 different atoms. Each is unique chemically and physically. Elements are identified by the number of protons in the nucleus, which is given as the atomic number on the periodic table. Neutral atoms contain an equal number of electrons around the nucleus as protons in the nucleus. The electrons are arranged in energy levels as described in the quantum model.