Protons, Number

Comphcated theoretical calculations, based on filled shell (magic number) and other nuclear stabiUty considerations, have led to extrapolations to the far transuranium region (2,26,27). These suggest the existence of closed nucleon shells at Z = 114 (proton number) and N = 184 (neutron number) that exhibit great resistance to decay by spontaneous fission, the main cause of instabiUty for the heaviest elements. Eadier considerations had suggested a closed shell at Z = 126, by analogy to the known shell at = 126, but this is not now considered to be important. 

The atomic number Z(number of protons in the nucleus) is shown as a left subscript. The mass number A (number of protons + number of neutrons in the nucleus) appears as a left superscript. 

Nuclear symbol Charge Number of protons Number of neutrons Number of electrons g 60... 

Fig. 8. A curve of proton number Z as a function of neutron number N, calculated as described in the text. The horizontal lines show the ranges of stablg isotopes for alternate Z-even elements (for large Z the four most stable isotopes).

Element Symbol Atomic (proton) number No. electrons No. electrons in 1st shell in 2nd shell No. electrons in 3rd shell No. electrons in 4th shell... 

Symbol Atomic Number Mass Number Number of Protons Number of Electrons Number of Neutrons... 

Z = number of protons = number of electrons in uncombined atom... 

Symbol of Species Number of Protons Number of Neutrons Number of Electrons... 

Radionuclide An atom that is distinguished by its nucleus composition (number of protons, number of neutrons, energy content), atomic number, mass number, and atomic mass. 

N, the mass number = number of protons + number of neutrons... 

Atoms of the same element (accept same atomic number / proton number) (1) that differ only in the number of neutrons (accept different mass number... 

All elements, by definition, have a unique proton number, but some also have a unique number of neutrons (at least, in naturally occurring forms) and therefore a unique atomic weight - examples are gold (Au Z = 79, N = 118, giving A =197), bismuth (Bi Z = 83, N = 126, A = 209), and at the lighter end of the scale, fluorine (F Z = 9, N = 10, A = 19) and sodium (Na Z = 11, N= 12, A = 23). Such behavior is, however, rare in the periodic table, where the vast majority of natural stable elements can exist with two or more different neutron numbers in their nucleus. These are termed isotopes. Isotopes of the same element have the same number of protons in their nucleus (and hence orbital electrons, and hence chemical properties), but... 

Figure 10.2 The radioactive stability of the elements. The x axis is proton number (up to Z = 83, bismuth), the y axis the neutron number (N). Stable isotopes are shown in black and radioactive isotopes in grey, indicating the relative excess of radioactive isotopes over stable isotopes in nature, and the fact that as proton number increases, the neutron number has to increase faster to maintain stability. The basic data for this figure are given in Appendix VI.

A fourth mode of decay, which results in the nucleus reducing its proton number by one, is called electron capture, whereby a proton from the nucleus captures one of the extranuclear (orbital) electrons, converting itself into a nuclear neutron. The daughter is isobaric (same mass) with the parent, but has a proton number which is decreased by one ... 

N = neutron number, Z = proton number. The atomic number A = Z + N. 

Electronegativity is the tendency of an atom to attract the bonding electrons within a compound to itself. It depends upon the nuclear charge (proton number) and the atomic radius of the atom. It is these factors that control the ionization energy of the atom which in turn is related to the ability of an atom to attract electrons. 

Van der Waals forces depend upon the electron density of the atoms. Increasing number of atoms in a molecule increases the van der Waals attractive force. Since the electron number of a neutral atom is equal to its proton number, atoms which have a large proton number have strong van der Waals forces between their molecules. Therefore, van der Waals forces are stronger between molecules with high molecular masses. 

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