Atomic number isotopes

When atoms are of similar atomic number (isotopes) they are arranged in decreasing mass number. 

I he awmic number or proron number, Z, of an element is the number of protons in the nucleus of an atom of the element. The mass number or nucleon number.. . is the number of protons and neutrons in ibe nucleus of an atom Isoropes of an element differ in mass number but have the same atomic number. Isotopes arc represented as Symbol, e.g. C. Protons are represented as jH. electrons (d-particles) as. neutrons as l,n. and O particles as l(e. In the equation for a nuclear reaction, the sum of the mass numbers is the same on both sides, and the sum of the atomic numbers is the. same on both sides of the equation. 

Element (Atomic number) Isotope Relative atomic mass Abundmice (%) Isot( -averaged atomic weight... 

Atomic Number, Isotopes, and Mass Number of Isotopes... 

Atomic Number Isotope Natural Abundance Z-Capture Units... 

All elements of atomic number greater than 83 exhibit radioactive decay K, Rb, Ir and a few other light elements emit p particles. The heavy elements decay through various isotopes until a stable nucleus is reached. Known half-lives range from seconds to 10 years. 

The use of larger particles in the cyclotron, for example carbon, nitrogen or oxygen ions, enabled elements of several units of atomic number beyond uranium to be synthesised. Einsteinium and fermium were obtained by this method and separated by ion-exchange. and indeed first identified by the appearance of their concentration peaks on the elution graph at the places expected for atomic numbers 99 and 100. The concentrations available when this was done were measured not in gcm but in atoms cm. The same elements became available in greater quantity when the first hydrogen bomb was exploded, when they were found in the fission products. Element 101, mendelevium, was made by a-particle bombardment of einsteinium, and nobelium (102) by fusion of curium and the carbon-13 isotope. 

Nowadays, chemical elements are represented in abbreviated form [2]. Each element has its ovm symbol, which typically consists of the initial upper-case letter of the scientific name and, in most cases, is followed by an additional characteristic lower-case letter. Together with the chemical symbol, additional information can be included such as the total number of protons and neutrons in the nucleus, the atomic number (the number of protons in the nucleus) thus isotopes can be distinguished, e.g., The charge value and, finally, the number of atoms which are present in the molecule can be given (Figure 2-3). For example, dioxygen is represented by O2. 

Fm and heavier isotopes can be produced by intense neutron irradiation of lower elements, such as plutonium, using a process of successive neutron capture interspersed with beta decays until these mass numbers and atomic numbers are reached. 

Though individual atoms always have an integer number of amus, the atomic mass on the periodic table is stated as a decimal number because it is an average of the various isotopes of an element. Isotopes can have a weight either more or less than the average. The average number of neutrons for an element can be found by subtracting the number of protons (atomic number) from the atomic mass. 

Atoms with the same number of protons but a different number of neutrons are called isotopes. To identify an isotope we use the symbol E, where E is the element s atomic symbol, Z is the element s atomic number (which is the number of protons), and A is the element s atomic mass number (which is the sum of the number of protons and neutrons). Although isotopes of a given element have the same chemical properties, their nuclear properties are different. The most important difference between isotopes is their stability. The nuclear configuration of a stable isotope remains constant with time. Unstable isotopes, however, spontaneously disintegrate, emitting radioactive particles as they transform into a more stable form. 

The most important types of radioactive particles are alpha particles, beta particles, gamma rays, and X-rays. An alpha particle, which is symbolized as a, is equivalent to a helium nucleus, fHe. Thus, emission of an alpha particle results in a new isotope whose atomic number and atomic mass number are, respectively, 2 and 4 less than that for the unstable parent isotope. 

Partial mass spectra showing the isotope patterns in the molecular ion regions for ions containing carbon and (a) only one chlorine atom, (b) only one bromine atom, and (c) one chlorine and one bromine atom. The isotope patterns are quite different from each other. Note how the halogen isotope ratios appear very clearly as 3 1 for chlorine in (a), 1 1 for bromine in (b), and 3 4 1 for chlorine and bromine in (c). If the numbers of halogens were not known, the pattern could be used in a reverse sense to decide their number. 

For organometailic compounds, the situation becomes even more complicated because the presence of elements such as platinum, iron, and copper introduces more complex isotopic patterns. In a very general sense, for inorganic chemistry, as atomic number increases, the number of isotopes occurring naturally for any one element can increase considerably. An element of small atomic number, lithium, has only two natural isotopes, but tin has ten, xenon has nine, and mercury has seven isotopes. This general phenomenon should be approached with caution because, for example, yttrium of atomic mass 89 is monoisotopic, and iridium has just two natural isotopes at masses 191 and 193. Nevertheless, the occurrence and variation in patterns of multi-isotopic elements often make their mass spectrometric identification easy, as depicted for the cases of dimethylmercury and dimethylplatinum in Figure 47.4. 

Natural radioactive processes in themselves give rise to changes of one element into another. Emission of an alpha particle reduces the atomic number of an element by two units, and emission of a beta particle increases the atomic number by one unit. Thus, for isotopes of elements near... 

Ratios of lead isotopes depend on the source of the lead. They vary because lead is an end product of radioactive decay from elements of greater atomic number. 

Plutonium (Pu) is an artificial element of atomic number 94 that has its main radioactive isotopes at 2 °Pu and Pu. The major sources of this element arise from the manufacture and detonation of nuclear weapons and from nuclear reactors. The fallout from detonations and discharges of nuclear waste are the major sources of plutonium contamination of the environment, where it is trapped in soils and plant or animal life. Since the contamination levels are generally very low, a sensitive technique is needed to estimate its concentration. However, not only the total amount can be estimated. Measurement of the isotope ratio provides information about its likely... 

Atoms of many other elements contain nuclei that have different numbers of neutrons. For example, carbon (Z = 6) can have six neutrons (M = 6 + 6 = 12), seven neutrons (M = 13), or eight neutrons (M = 14). Atoms of the same atomic number but having different numbers of neutrons (and different atomic masses) are called isotopes. Thus, naturally occurring carbon has three isotopes, for which Z = P = 6 and N = 6 or 7 or 8. These are written. ... 

Many elements exist as isotopes, viz., atoms of the same atomic number containing different ratios of protons to neutrons. 

A simple example occurs with hydrogen, which occurs naturally as three isotopes (hydrogen, deuterium, tritium), all of atomic number 1 but having atomic masses of 1, 2, and 3 respectively. 

On the basis of the simplest projections it is expected that the half-Hves of the elements beyond element 109 will become shorter as the atomic number is increased, and this is tme even for the isotopes with the longest half-life for each element. This is illustrated by Figure 6, in which the half-Hves... 

The effects of a rather distinct deformed shell at = 152 were clearly seen as early as 1954 in the alpha-decay energies of isotopes of californium, einsteinium, and fermium. In fact, a number of authors have suggested that the entire transuranium region is stabilized by shell effects with an influence that increases markedly with atomic number. Thus the effects of shell substmcture lead to an increase in spontaneous fission half-Hves of up to about 15 orders of magnitude for the heavy transuranium elements, the heaviest of which would otherwise have half-Hves of the order of those for a compound nucleus (lO " s or less) and not of milliseconds or longer, as found experimentally. This gives hope for the synthesis and identification of several elements beyond the present heaviest (element 109) and suggest that the peninsula of nuclei with measurable half-Hves may extend up to the island of stabiHty at Z = 114 andA = 184. 

Iodine [7553-56-2] I, atomic number 53, atomic weight 126.9044, is a nonmetaUic element belonging to the halogen family in Group 17 (VIIA) of the Periodic Table. The only stable isotope has a mass number of 127. There are 22 other iodine isotopes having masses between 117 and 139 14 of these isotopes yield significant radiation. 

Lead, atomic number 82, is a member of Group 14 (IVA) of the Periodic Table. Ordinary lead is bluish grey and is a mixture of isotopes of mass number 204 (15%), 206 (23.6%), 207 (22.6%), and 208 (52.3%). The average atomic weight of lead from different origins may vary as much as 0.04 units. The stable isotopes are products of decay of three naturally radioactive elements (see Radioactivity, natural) comes from the uranium series (see Uraniumand... 

Magnesium [7439-95-4] atomic number 12, is in Group 2 (IIA) of the Periodic Table between beryllium and calcium. It has an electronic configuration of 1T2T2 3T and a valence of two. The element occurs as three isotopes with mass numbers 24, 25, and 26 existing in the relative frequencies of 77, 11.5, and 11.1%, respectively. 

Manganese [7439-96-5] atomic number 25, atomic weight 54.94, belongs to Group 7 (VII) ia the Periodic Table. Its isotopes are Mn, Mn, Mn,... 

Tellurium illustrates the rule that elements having even atomic numbers have more isotopes than elements having odd atomic numbers. 

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