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Explanation of the Chemical Elements - Succeed in Chemistry. Also refer to physics, physical science, atom, proton, neutron, electron, nucleus, atomic number, weight, isotope, nuclear, stable, Ron Kurtus, School for Champions. Copyright © Restrictions Chemical Elementsby Ron Kurtus (revised 24 July 2007) A chemical element (usually just called an element) is a class of atoms with a specific number of protons in their nuclei (plural of nucleus in Latin). Each element has its own name and is usually listed according to its atomic number. Isotopes of an element have different numbers of neutrons. Often the average atomic weight of an element is also stated. This number takes into account the percentages of isotopes, the masses of the particles, and nuclear effects. The average atomic weight is approximately the number of protons and neutrons of the most common isotope of the element. Questions you may have include:
This lesson will answer those questions. There is a mini-quiz near the end of the lesson. Atomic numberThe elements are listed according to their atomic number. The atomic number is designated by the number of protons in the nucleus. For example, Hydrogen has one proton, Helium has two protons, Oxygen has eight protons, and so on. Since the number of electrons equals the number of protons in an electrically stable atom, the atomic number determines many of the chemical characteristics of the element. This is shown in the Periodic Table. (See Periodic Table for more information.) Average atomic weightThe atomic weight of an atom was originally defined as a sum of its protons and neutrons. The unit of measurement is the atomic mass unit (amu or u). Mass defectLater, it was found that some mass is lost to binding energy required to hold the nucleus together. This is called the mass defect and is the principle behind nuclear energy, according the to the famous equation E = mc2. Thus the atomic weight of an individual atom is slightly different than the number of protons and neutrons. IsotopesAn element has several different number of neutrons in its nucleus. Each is called an isotope of that element. For example, Oxygen typically has 8 protons and 8 neutrons in its nucleus, with an atomic weight of about 16 u. But there is a very small percentage of Oxygen atoms with 9 neutrons in their nuclei and atomic weight of approximately 17 u. There are even some atoms with 10 neutrons. Thus for the element Oxygen, taking into account for the mass defect and averaging the atomic weight for all its isotopes, you get an average atomic weight of 15.9994 u for Oxygen. Finding number of neutronsLooking on the list of elements below, you will see that the Average Atomic Weight is not integer. You can find the number of neutrons in the most common and stable nucleus of an element by simply rounding off the atomic weight and subtracting the atomic number (number of protons). For example, Magnesium (Mg) is number 12 and has an average atomic weight of 24.3050 u. This rounds off to 24. Thus the number of protons in the most common isotope of Magnesium is 24 - 12 = 12 neutrons. (See Atomic Weight in Physical Science for more information.) List of elementsFollowing is a list of all the elements, according to atomic number. Elements with the weight in [brackets] are so unstable that scientists have not been able to accurately measure the weight. All of the elements after Uranium (number 92) are artificial and unstable. An artificial element is one that is so unstable that it does not occur in nature. High energy atomic collisions can manufacture such an element. It immediately decays into a stable element.
SummaryAn element is a basic chemical unit. Elements have an atomic number and atomic weight assigned to them. There are 92 natural elements, plus some that have been artificially created. Artificial elements are highly unstable and usually exist for only a fraction of a second. ResourcesThe following resources provide information on this subject: WebsitesBooks
Top-rated books on Physical Science MiscellaneousMini-quiz to check your understanding1. What does the atomic number designate? 2. If the average atomic weight of atomic number 11 (Sodium) is 22.989770, how many neutrons are in its most common isotope? 3. Why are the atomic weights of the unstable elements whole numbers? If you got all three correct, you are on your way to becoming a Champion in Chemistry. If you had problems, you had better look over the material again. What do you think?Do you have any questions, comments, or opinions on this subject? If so, send an email with your feedback. We will try to get back to you as soon as possible. Share linkFeel free to establish a link from your website to pages in this site. 
Or use our form to send this link to yourself or a friend. Students and researchersThe Web address of this page is Please include it as a reference in your report, document, or thesis. Where can you go from here?
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