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Q: atomic mass vs atomic number ( Answered,   1 Comment )
Subject: atomic mass vs atomic number
Category: Science
Asked by: michelazar-ga
List Price: $2.00
Posted: 28 Feb 2005 20:08 PST
Expires: 30 Mar 2005 20:08 PST
Question ID: 482668
exists some relation between the atomic mass and the atomic number?
Subject: Re: atomic mass vs atomic number
Answered By: siliconsamurai-ga on 01 Mar 2005 08:47 PST
Hi, thank you for submitting your question to Answers.Google, I hope I
can provide the information you are seeking.

Yes, there is a definite linkage.

The atomic number of an element is the number of protons (hence the
number of electrons) associated with the atom.

The reason you see integers describing the atomic number is that all
atoms with the same number of protons are the same element.

Isotopes of the element have different numbers of neutrons in the nucleus.

The atomic weight of an element is the average weight of the nucleus
which includes the normally occurring percentage of each isotope for
the element.

For example, Carbon is almost all (99%) carbon-12. The atomic number
is 6 meaning there are six protons. The atomic weight is 12.01115?
because there are few other carbon isotopes other than the one where
there are 6 protons and 6 neutrons.

The connection between the two numbers is complex but not that
difficult to understand in general terms.

For elements of low atomic number a nucleus is most stable when the
number of neutrons and protons are about equal. When the number of
neutrons is different from the number of protons the nucleus generally
becomes more unstable (radioactive) and will spontaneously decay into
other elements.

This 1:1 ration is not an exact relationship and alters significantly
as the atomic number increases. The higher the number of protons, the
higher the ratio of protons required for stability, going up near 2:1
neutrons:protons at the higher numbers and even higher.

A chart of this is referred to as the belt of stability.

You can find more information (at a considerably more complex level) at


Thank you again for turning to Answers.Google for help.
Subject: Re: atomic mass vs atomic number
From: xarqi-ga on 28 Feb 2005 23:23 PST
Broadly speaking, the higher one is, the higher the other is.

Your question, phrased another way, might be, what determines the
number of neutrons that can combine with a given number of protons to
form a stable nucleus?

It's a complex issue.

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