QUESTION #109

What are the number of neutrons in each of elements? (Not isotopes of elements).

Asked by: Joe Aster

All elements, except the most common form of hydrogen, contain neutrons to help hold the positively charged protons in their nucleus together. Neutrons add to the strong nuclear force without adding to the mutually repulsive electrical force of the protons.

Every element can exist in different forms, called isotopes. Each isotope of an element contains the same number of protons but different numbers of neutrons. While some isotopes are stable and others are not, they are ALL called isotopes just as all siblings in a family are brothers or sisters. Even though there is usually a more abundant form of each element's nucleus, there is no one 'main' nucleus with a 'non-isotope' designation as your question implies.

If you look at the isotopes of different elements, the general rule is that the number of neutrons is similar to the number of protons in nuclei at the beginning of the periodic table (low number of protons). Carbon, for example, has a stable nucleus when its 6 protons are joined by 6 neutrons. When you get to elements with a larger number of protons in their nucleus, the ratio of neutrons to protons increases. Uranium, for example, has the largest naturally occurring nucleus with 92 protons and over 140 neutrons.
Answered by: Paul Walorski, B.A. Physics, Part-time Physics Instructor

You can figure out the most common configuration of elements by looking at the periodic table of elements. There, elements are arranged according to their atomic number - the number of protons in the nuclei. The notation is as follows:

AZX

where, A is the mass number of the element's nuclei, and Z is the atomic number (X stands for the element symbol, for example: H is for hydrogen, O is for oxygen, Na for sodium, etc.) The mass number gives you the total number of protons and neutrons in the nucleus of that element. Therefore, the number of neutrons is given by A-Z.
Answered by: Anton Skorucak, M.S. Physics, PhysLink.com Editor

The identity of an element is the number of protons in its nucleus. Since protons repel each other, neutrons must be present in the nucleus to hold the protons together. For example, carbon has 6 protons in its nucleus by definition. To hold these protons together, it takes at least 6 neutrons. However, carbon atoms may also have 7 or 8 neutrons. Since carbon comes in more than one variety due to differing numbers of neutrons, carbon is said to come in more than one 'isotope'. All atoms are 'isotopes'. But each element has its most common isotope. For carbon it is 'carbon 12' meaning 6 protons plus 6 neutrons. Oxygen's most common isotope is 'oxygen 16', i.e. 8 protons and 8 neutrons.

Since many isotopes are unstable (radioactive), some people think the word 'isotope' implies radioactivity, but really it doesn't. Since there are over 100 elements, I can't give you the most common isotope of all of them. But here are a few. I will give you the proton number, followed by the element's name, followed by the number of neutrons: 1hydrogen0 - 2helium2- 6carbon6 - 8oxygen8- 7nitrogen7- 26iron30- 92uranium146.

Generally, the more protons in the atom, the higher the proportion of neutrons needed to hold it together. Beyond 83 protons, no amount of neutrons can hold it together forever.
Answered by: Dennis Gordon, Self Educated