The problem is that you will also record lines for the unfragmented Cl2+ ions. The abundance of the isotopes: The relative sizes of the peaks gives you a direct measure of the relative abundances of the isotopes. A simple average of 10 and 11 is, of course, 10.5. In this case, the 5 isotopes (with their relative percentage abundances) are: Suppose you had 100 typical atoms of zirconium. 51.5 of these would be 90Zr, 11.2 would be 91Zr and so on. Both atoms could be 35Cl, both atoms could be 37Cl, or you could have one of each sort. These ions won't be particularly stable, and some will fall apart to give a chlorine atom and a Cl+ ion. The example coming up should make that clear. We'll look at its mass spectrum to show the sort of problems involved. MASS SPECTRA Tables 1, 2, and 3 tabulate the mass spectra for the Sb, As, and P compounds, respectively. The total may look as if it exceeds 100 percent, but that is because the mass spectrum works with relative percentage isotope abundances. ))�)@ @ @ RJ�СC���A�n����B�g�}V�b��"�f@ @ @ HJ�={�L�8�{������ ���0`Μ9LJ This page looks at the information you can get from the mass spectrum of an element. In this case, the two isotopes (with their relative abundances) are: The relative atomic mass (RAM) of an element is given the symbol Ar and is defined as: A "weighted average" allows for the fact that there won't be equal amounts of the various isotopes. 2099 Our answer of 10.8 allows for the fact that there are a lot more of the heavier isotope of boron - and so the "weighted" average ought to be closer to that. © 2003-2020 Chegg Inc. All rights reserved. The relative sizes of the peaks gives you a direct measure of the relative abundances of the isotopes. endobj Copyright 1993-2020 Mark Winter [ The University of Sheffield and WebElements Ltd, UK]. 6 0 obj Which of the following elements has the mass spectrum shown here? We are assuming (and shall do all through this page) that all the ions recorded have a charge of 1+. The mass of antimony-121 is 120.904 amu and the mass of antimony-123 is 122.904 amu. Just remember that the ratio is 9:6:1. The problem is that chlorine consists of molecules, not individual atoms. /Cs1 7 0 R >> /Font << /TT2 12 0 R /TT4 20 0 R >> /XObject << /Im5 21 0 R Mass spectrometry (MS) coupled to a chromatographic system is a powerful tool due to its high selectivity and sensitivity. The number of isotopes. Again you can find these relative abundances by measuring the lines on the stick diagram. We'll look at its mass spectrum to show the sort of problems involved. 2 0 obj Naturally occurring isotopes This table shows information about … Go To: Top, Mass spectrum (electron ionization), References Data from NIST Standard Reference Database 69: NIST Chemistry WebBook The National Institute of Standards and Technology (NIST) … mzCloud ‒ Free Online Mass Spectrometry Database That's why you've got the chlorine mass spectrum in two separate bits so far. Example \(\PageIndex{2}\): The Mass Spectrum of Zirconium. The rearrangement ion [F 3 C C C C C CF 2] +] gives the strongest peak in each spectrum. 91.3 is the relative atomic mass of zirconium. That would give you total masses of the Cl2+ ion of: That means that you would get a set of lines in the m/z = 70 region looking like this: These lines would be in addition to the lines at 35 and 37. The average mass of these 123 atoms would be 1330 / 123 = 10.8 (to 3 significant figures). 51.5 of these would be 90Zr, 11.2 would be 91Zr and so on. /Im4 17 0 R /Im6 23 0 R /Im3 15 0 R /Im2 13 0 R /Im1 8 0 R >> >> The mass spectrum … Our answer of 10.8 allows for the fact that there are a lot more of the heavier isotope of boron - and so the "weighted" average ought to be closer to that. That means that the mass/charge ratio (m/z) gives you the mass of the isotope directly. All rights reserved. You might suppose that the mass spectrum would look like this: You would be wrong! %��������� Relative Abundance O 118 119 120 121 122 123 124 125 Atomic Mass (amu) Relative Abundance O 118 119 120 121 122 123 124 125 Atomic Mass (amu) Relative Abundance 118 119 120 121 122 123 124 125 Atomic Mass (amu). This time, the relative abundances are given as percentages. 1.2: Identify the elements from the mass spectrum: (a) (b) (c) (d) 2. Monatomic elements include all those except for things like chlorine, Cl2, with molecules containing more than one atom. N&P�Z�f͚ :t۶m)�#� � � �����/^\�lYff��8�� k֬����o+**�z�j#pk � � � �������ٳgw���fe˖U,��lɒ%gϞU,��8�2 � � � I,p���u�ֽ��Kw�q���� The number of isotopes: The 5 peaks in the mass spectrum shows that there are 5 isotopes of zirconium - with relative isotopic masses of 90, 91, 92, 94 and 96 on the 12C scale. So let's say it's this pure element.