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The Nucleus Help (page 2)

By — McGraw-Hill Professional
Updated on Sep 5, 2011

Atomic Number

According to modern atomic theory, every proton in the universe is exactly like every other. Neutrons are all alike too. The number of protons in an element’s nucleus, the atomic number , gives that element its identity.

The element with three protons is lithium , a light metal that reacts easily with gases such as oxygen or chlorine. Lithium always has three protons; conversely, any element with three protons in its nucleus must be lithium. The element with four protons is beryllium , also a metal. Carbon has six protons in its nucleus, nitrogen has seven, and oxygen has eight. In general, as the number of protons in an element’s nucleus increases, the number of neutrons also increases. Elements with high atomic numbers, such as lead, are therefore much more dense than elements with low atomic numbers, such as carbon. Perhaps you’ve compared a lead shot with a piece of coal of similar size and noticed this difference.

If you could somehow add two protons to the nucleus of every atom in a sample of carbon, you would end up with an equal number of atoms of oxygen. However, this is much easier said than done, even with a single atom. It is possible to change one element into another; the Sun does it all the time, fusing hydrogen into helium. The process is far from trivial, though. In ancient times, alchemists tried to do this; the most well-known example of their pursuits was the quest to turn lead (atomic number 82) into gold (atomic number 79). As far as anyone knows, they never succeeded. It was not until the 1940s, when the first atomic bombs were tested, that elements actually were “morphed” by human beings. The results were quite different from anything the alchemists ever strove for.

Table 9-1 lists all the known elements in alphabetical order, with the names of the elements in the first column, the standard chemical symbols in the second column, and the atomic numbers in the third column.

Table 9-1 The Chemical Elements in Alphabetical Order by Name, Including Chemical Symbols and Atomic Numbers 1 through 118 (As of the time of writing, there were no known elements with atomic numbers 113, 115, or 117.)

Particles of Matter The Nucleus Isotopes

Particles of Matter The Nucleus Isotopes

Particles of Matter The Nucleus Isotopes

Particles of Matter The Nucleus Isotopes

Particles of Matter The Nucleus Isotopes

Isotopes

In the individual atoms of a given element, such as oxygen, the number of neutrons can vary. Regardless of the number of neutrons, however, the element keeps its identity based on the atomic number. Differing numbers of neutrons result in various isotopes for a specific material element.

Each element has one particular isotope that is found most often in nature. However, all elements have more than one isotope, and some have many. Changing the number of neutrons in an element’s nucleus results in a difference in the mass, as well as a difference in the density, of the element. Thus, for example, hydrogen containing a neutron or two in the nucleus, along with the proton, is called heavy hydrogen . The naturally occurring form of uranium has three more neutrons in its nucleus than the type that is notorious for use in atomic weapons.

Adding or taking away neutrons from the nucleus of an element is not quite as farfetched a business as adding or taking away protons, but it is still a task generally relegated to high-energy physics. You can’t simply take a balloon filled with air, which is approximately 78 percent nitrogen, and make it more massive by injecting neutrons into the nitrogen nuclei.

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