Isotope One of two or more atoms

ISOTOPE One of two or more atoms having the same atomic number but different mass number. 

Isotope One of two or more atoms with the same atomic number (the same chemical element) but with different atomic weights isotopes usually have very nearly the same chemical properties but somewhat different physical properties, i. v. Abbreviation for intravenous (administration). 

Isotope One of two or more atoms of the same element that have the same number of protons in their nucleus but different numbers of neutrons. Hydrogen (1 proton, no neutrons), deuterium (1 proton, 1 neutron), and tritium (1 proton, 2 neutrons) are isotopes of hydrogen. Most elements in nature consist of a mixture of isotopes. See isotope SEPARATION. 

Isotope One of two or more forms of the same chemical element differing only in the number of neutrons in the nucleus and therefore in relative atomic mass, e.g. carbon 12,13,14. 

Figures 5.19b and 5.19c represent the mass spectra of compounds with single chlorine and bromine atoms, respectively. Roughly, in the case of chlorine the ratio of intensities of A and A + 2 peaks is 3 to 1, and in case of bromine, 1 to 1. One should take into account that the presence of several atoms of A + 2 elements in the molecule results in the appearance of intense peaks M + 4, M + 6, etc., that is, the presence of two or more atoms of A + 2 elements in an ion again gives a unique ratio of isotopic peaks in the...

Isotope l-s3- top [is- + Gk topos place] (1913) n. In chemistry, one of two or more forms of an element ( nuclides ) having the same number of protons in the nucleus but differing in mass number because of different numbers of neutrons. Natural elements are usually mixtures of isotopes thus the observed atomic weights are average values weighted by isotopic relative abundance. Serway RA, Faugh JS, Bennett CV (2005) College physics. Thomas, New York. 

We have seen that all atoms of the same element have the same number of protons and electrons. However, the atoms of any one element are not entirely identical because the atoms of most elements have different numbers of neutrons. When a sample of an element consists of two or more atoms with differing numbers of neutrons, those atoms are called isotopes. 

ISOTOPE. An isotope is one of nvo or more nuclides ibal have the same number of protons in iheir nuclei. An> two isotopes have ihe same aiuniic number. However. their mass numbers, A. differ. Isotope is a term that stems from the Greek words, isos tsume) and topos (place , to designate substances having different atomic weights and vei having chemical properties so much alike I hat in the early days ol research ii was nor possible to perform ti chemical separation ol the isotope of a given element. 

In 1808 John Dalton proposed his atomic theory, which included the statement that when atoms of two or more elements combine to form a compound, they combine in a definite ratio by number of atoms and by mass. This is called the law of definite proportions. This provided a means to determine the mass of one atom relative to another. It was necessary to assign a mass to one element to find the mass of another element in a compound. Today we use the most common carbon isotope, assigned a mass of 12.00 atomic mass units (amu), as the basis for comparative weights of the atoms. 

The early pioneers of chemistry, trying to verify Dalton s atomic theory, could not measure the mass of individual atoms. The best they could do was to measure the masses of equal numbers of atoms (or other known ratios of atoms) of two (or more) elements at a time, to determine their relative masses. They established one element as a standard, gave it an arbitrary value of atomic mass, and used that value to establish the atomic mass scale. The last naturally occurring mixture of isotopes that was used as a standard was oxygen, defined as having an atomic mass of exactly 16 atomic mass units (amu). That standard has been replaced see the next subsection. The atomic mass unit is tiny it takes... 

To know more about molecular weights, one must first become familiar with the concept of atomic weights. Because an element (e.g., carbon, oxygen, sulfur, etc.) often exists as a mixture of two or more (stable and unstable forms) natural isotopes that have the same number of protons but differ in the number of neutrons, atomic masses of these isotopes are slightly different from each other. In this case, atomic masses are averaged and the ratio of the resultant value to some standard is defined as the atomic weight of the element. 

The small peak for ethyl benzene at miz 107 in T ig-ure 20-1 is due to the presence of in the molecules. The intensities of peaks due to incorporation of two or more X atoms in ethyl benzene can be predicted with good precision but are normally so small as to be undetectable because of the low probabilils of there being more than one C atom in a small molecule. As will )c shown in Section 20D-1. isotope peaks. sometimes provide a useful means for determining the formula for a compound. 

The modern definition of isotope refers to two or more forms of an element having different atomic masses. The original definition, by Soddy, was derived not from comparisons of atomic masses, but from studies of decay of chemically nonseparable, but clearly different, forms of the same radioactive elements. Thomson s 1907 experiment on canal rays passing through neon gas, described earlier, produced two parabolic paths, one corresponding to mass 20 and the other to mass 22. While this was the first evidence for isotopes of light, nomadioactive elements, the data were relatively crude and knowledge of atomic structure was insufficient to fully understand the result. 

The possibility of having different numbers of neutrons combined with one given number of protons to form nuclei leads to some interesting results. For example, three different kinds of hydrogen atoms are known to exist. Each kind of atom contains one proton and one electron, so all have an atomic number of 1. However, the nuclei of the different kinds of hydrogen atoms contain different numbers of neutrons. The most common kind has no neutrons in the nucleus, the next most common has one, and the least common kind has two. The sum of the number of protons and the number of neutrons in a nucleus is called the mass number and is represented by the symbol A. Thus, the three kinds of hydrogen atoms all have atomic numbers of 1 and mass numbers of 1, 2, and 3, respectively. Atoms that have the same atomic number but different mass numbers are called isotopes. Most elements are made up of mixtures of two or more isotopes. When it is important to... 

In laboratory work, a chemist generally nses samples with many atoms that contain all the different isotopes of an element. Becanse each kind of isotope has a different mass, chemists have calculated an atomic mass for an average atom, which is a weighted average of the masses of all the naturally occurring isotopes of that element. On the periodic table, the atomic mass is the number including decimal places that is shown below the symbol of each element. Most of the elements consist of two or more isotopes, which is one reason that the atomic masses on the periodic table are seldom whole numbers. 

Most elements are composed of mixtures of two or more isotopes so that the atoms in a sample of the element are not all of the same mass but are present in their naturally occurring proportions. Thus, in one mole of carbon, most of the atoms are carbon-12, but some are carbon-13. In one mole of oxygen, most of the atoms are oxygen-16, but some are oxygen-17 and some are oxygen-18. As a result,... 

Most nuclear reactions involve the breaking apart of the nucleus into two or more different elements or subatomic particles. If we know all but one of the particles, then the unknown particle can be determined by balancing the nuclear equation. When chemical equations are balanced, we add coefficients to ensure that there are the same number of each type of atom on both the left and right of the reaction arrow. However, in order to balance nuclear equations we ensure that there is the same sum of both mass numbers and atomic numbers on the left and right of the reaction arrow. Recall that we can represent a specific isotope of an element by the following symbolization ... 

Isotope effects on equilibria have been formulated earlier in this chapter in terms of ratios of (s2/si)f values, referred to as reduced isotopic partition function ratios. From Equation 4.80, we recognize that the true value of the isotope effect is found by multiplying the ratio of reduced isotopic partition function ratios by ratios of s2/si values. Using Equation 4.116 one now knows how to calculate s2/si from ratios of factorials. Note well that symmetry numbers only enter when a molecule contains two or more identical atoms. Also note that at high temperature (s2/si)f approaches unity so that the high temperature equilibrium constant is the symmetry number factor. 

Even if the analyte is chemically perfectly pure it represents a mixture of different isotopic compositions, provided it is not composed of monoisotopic elements only. Therefore, a mass spectrum is normally composed of superimpositions of the mass spectra of all isotopic species involved. [11] The isotopic distribution or isotopic pattern of molecules containing one chlorine or bromine atom is listed in Table 3.1. But what about molecules containing two or more di-isotopic or even polyisotopic elements While it may seem, at the first glance, to complicate the interpretation of mass spectra, isotopic patterns are in fact an ideal source of analytical information. 

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