1: Basic Structure of the Atom

In the atomic models that are in use today, an atom consists of a positively charged nucleus, with negatively charged electrons moving around it. The nucleus consists of positively charged protons, and neutrons without charge. The role of the neutrons is to keep the positively charged protons together.

Since the charge of one electron is the same as that of one proton, the number of electrons and protons in an electrically neutral atom will be the same.

The masses of protons and neutrons are virtually the same, viz. 1.7 x 10-24 g; the mass of an electron can be neglected. However, the atoms volume is determined by the electrons, whereas the nucleus contributes very little to the volume.

The different elements are characterised by their number of protons (or electrons); thus the simplest element, hydrogen (H), has one proton, whereas the element Lawrencium (Lr) has 103.

Following hydrogen, the atoms of the element helium (He) are composed of two protons and two neutrons; lithium (Li) has three protons and 4 neutrons (see fig. 1).

Figure 1:  Schematic presentation of the atomic structure of the three simplest elements; typical size: 0.03 nm. The red spheres represent protons, the blue spheres represent neutrons, and the black dots represent electrons. [I. Heiming]

The following video shows an animation of the basic structure of an atom:

Basic Atomic Structure (by mtchemers, 1:56 min)



  • S. Hoenig, 2001. Basic training in chemistry, pp. 1. Kluwer Academic/Plenum Publishers, New York.
  • CK-12 Foundation (S. Bewick et al.), 2016. Map: Introductory Chemistry (CK-12), ch. 4.16: Atomic Nucleus. Libre Texts/UC Davis. http://chem.libretexts.org/Textbook_Maps/Introductory_Chemistry_Textbook_Maps/Map%3A_Introductory_Chemistry_(CK-12)/04%3A_Atomic_Structure/4.14%3A_Atomic_Nucleus
Last modified: Tuesday, 15 November 2016, 12:18 PM