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protons and neutrons
It may seem contradictory that the nucleus of an atom sticks together when we know that like charges repel. Why don't the protons repel each other? It does not seem to fit the predicted pattern.
One theory suggests a model that arranges the protons and neutrons in a series of shells or energy levels like the electrons around the nucleus. The nucleus is held together by mesons, positrons, and neutrinos. Gamma rays are emitted when a proton or neutron drops to a lower energy level. Some nuclei are unstable. They have such a delicate balance of forces holding them together that the slightest disturbance will cause them to fly apart. This results in radioactive decay.
Stable nuclei are determined by the ratio of neutrons to protons. The greater the atomic number, the greater the number of neutrons necessary to keep the nucleus stable. The neutrons tend to act as a buffer among the protons, keeping them from repelling each other with such great force. Figure 9 shows the ratio n:p necessary to ensure a stable isotope.
Notice that as the atomic number increases, the number of neutrons must get larger to offset the increase in nuclear charge. Ratios that deviate very much from the curved line are unstable ratios and indicate radioactive isotopes of that particular element. No completely stable nuclei are in elements 83 and above. All isotopes of elements beyond bismuth (83) are unstable and radioactive.
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What is the number of atomic mass?
the mass of an atom of a chemical element expressed in atomic mass units. It is approximately equivalent to the number of protons and neutrons in the atom (the mass number)
How do you get the mass number by adding neutrons and the atomic number?
The mass number of an atom is the sum of the number of protons and neutrons in its nucleus. The atomic number represents the number of protons in an atom, so adding the atomic number to the number of neutrons will give you the mass number.
What comprises the atomic mass?
The atomic mass of an element is the sum of the number of protons and neutrons in the nucleus of an atom. It is approximately equal to the mass number of the atom, which is the total number of protons and neutrons. The atomic mass is typically expressed in atomic mass units (amu).
What is indicated by the atomic mass?
the mass of an atom of a chemical element expressed in atomic mass units. It is approximately equivalent to the number of protons and neutrons in the atom (the mass number) or to the average number allowing for the relative abundances of different isotopes.
What makes up an atoms mass number?
The atomic number of an element is the number of protons in the nucleus of the atom; each element has its own distinct number. The atomic mass is the mass of the nucleus of the atom: protons and neutrons. One proton is equivalent to one unit of mass, as is a neutron. You can figure out the number of neutrons in an atom by subtracting the atomic number (number of protons) from the atomic mass; the difference is the number of neutrons.
