Isotopes and Atomic Mass

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Isotopes and Atomic Mass How to write it The isotope of an element can be indicated in two ways: An element is distinguished by always having the same number of protons in the nucleus. Using the elements symbol (numbers can either be to the left or the right of the symbol): However, there can be a variable number of neutrons. 54 Atomic mass 54 An isotope of an element has the Fe Atomic number Fe 26 (may not be present) 26 same atomic number but has a different number of neutrons. This will affect the average mass Using the elements of an atom of an element. name: If we take a specific example it will become clear. Next > Iron- 54 Next > Example Question 1 Iron, atomic number 26, has four Carbon has an atomic number of 6. Its two naturally naturally occurring isotopes. Atomic mass number occurring isotopes are carbon 12 and carbon 13. 54 (number of nucleons) They are: How many neutrons do carbon 12 and 13 have? Fe Atomic number Fe-54, Fe-56, Fe-57, and Fe-58. 26 (number of protons) Carbon -12 Carbon -13 From the table, we can A) 6 7 see the number of protons neutrons nucleons B) 12 13 neutrons in each Fe-54 26 28 54 isotope’s nucleus. Fe-56 26 30 56 C) 7 6 A nucleon, is a Fe-57 26 31 57 D) 13 12 particle that is in the Fe-58 26 32 58 nucleus (either a proton or a neutron). Next > Next > Question 1 Abundance of each Isotope of Iron Carbon has an atomic number of 6. Its two naturally If a sample of iron was occurring isotopes are carbon 12 and carbon 13. examined with a mass How many neutrons do carbon 12 and 13 have? spectrometer, the abundance of each Carbon -12 Carbon -13 isotope could be A) 6 7 measured. B) 12 13 Luckily, tables exist giving Mass spectrometer us this information from Abundance in % C) 7 6 previous experiments. Fe-54 5.8 Fe-56 91.72 D) 13 12 How does this give us Fe-57 2.2 the average mass of Fe-58 0.28 Next > an atom? Next > 1 Question 2 Question 2 Copper has two naturally occurring isotopes (Cu-63 Copper has two naturally occurring isotopes (Cu-63 and Cu-65). and Cu-65). If copper 63 has an abundance of 69.17% what is If copper 63 has an abundance of 69.17% what is the abundance of copper 65? the abundance of copper 65? Give your answer as a percentage. Give your answer as a percentage. 30.83 (%) Next > Next > Calculation of Atomic Mass Number Calculation of Atomic Mass Number What is the atomic mass of each isotope? Multiply the mass Abundance Atomic mass Atomic mass of each isotope in % abundance Fe-54 53.93612 5.8 3.12829 Atomic mass by the Again, tables give us that Fe-56 55.93439 91.72 51.30302 Fe-54 53.93612 abundance, to data. (This is the atomic Fe-57 56.935396 2.2 1.25258 Fe-56 55.93439 give the mass relative to 1/12 of a Fe-58 57.933278 0.28 0.16221 Fe-57 56.935396 contribution of carbon atom). Total 55.8461 Fe-58 57.933278 each isotope. Summing the individual abundances, gives the total relative (average) atomic mass of iron. Next > Next > Calculation of Atomic Mass Number The periodic table gives the relative atomic mass of iron as 55.85. If we round up our calculation to 2 d.p. we also get 55.85. Next > 2 .

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An Introduction to Isotopic Calculations John M
An Introduction to Isotopic Calculations John M. Hayes ([email protected]) Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA, 30 September 2004 Abstract. These notes provide an introduction to: termed isotope effects. As a result of such effects, the • Methods for the expression of isotopic abundances, natural abundances of the stable isotopes of practically • Isotopic mass balances, and all elements involved in low-temperature geochemical • Isotope effects and their consequences in open and (< 200°C) and biological processes are not precisely con- closed systems. stant. Taking carbon as an example, the range of interest is roughly 0.00998 ≤ 13F ≤ 0.01121. Within that range, Notation. Absolute abundances of isotopes are com- differences as small as 0.00001 can provide information monly reported in terms of atom percent. For example, about the source of the carbon and about processes in 13 13 12 13 atom percent C = [ C/( C + C)]100 (1) which the carbon has participated. A closely related term is the fractional abundance The delta notation. Because the interesting isotopic 13 13 fractional abundance of C ≡ F differences between natural samples usually occur at and 13F = 13C/(12C + 13C) (2) beyond the third significant figure of the isotope ratio, it has become conventional to express isotopic abundances These variables deserve attention because they provide using a differential notation. To provide a concrete the only basis for perfectly accurate mass balances. example, it is far easier to say – and to remember – that Isotope ratios are also measures of the absolute abun- the isotope ratios of samples A and B differ by one part dance of isotopes; they are usually arranged so that the per thousand than to say that sample A has 0.3663 %15N more abundant isotope appears in the denominator and sample B has 0.3659 %15N.
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Iron-57 of Its Isotopes and Has an Sum of Protons + Neutrons 26 Fe Average Mass As Determined by a in the Nucleus
Elements - elements are pure homogeneous forms of matter Solid Liquid Gas Plamsa •constant volume & shape •constant volume but takes •varaible shape and volume •like a gas except it •very low compressibility on the shape of container that fills the container is composed of ions; •particles vibrate in place •low compressibility •high compressibility an ion is charged •highly ordered arrangement •random particle movement •complete freedom of motion atom or group of •do not flow or diffuse •moderate disorder •extreme disorder atoms. •strongest attractive forces •can flow and diffuse •flow and diffuse easily •examples: between particles •weaker attractive forces •weakest attractive forces - flames •generally more dense than •more dense than gases •least dense state - atmosphere of stars liquids •exert a pressure easily - a comet's tail Matter NO YES Pure Substance Can it be separated Mixture by physical means? Can it be decomposed by Is the mixture composition ordinary chemical means? identical throughout; uniform? NO YES YES NO element compound homogeneous heterogenous mixture mixture Co,Fe,S,H,O,C FeS, H2O, H2SO4 steel, air, blood, steam, wet iron, solution of sulfuric acid Cannot be separated Can be decomposed and rust on steel chemcially into simple chemcially separated Uniform appearance, Appearance, composition, substances into simple substances. composition and and properties are variable properties throughout in different parts of the sample Isotopes Is a mass number attached to the element? NO YES All atoms of the same element are not exactly alike mass number attached mass number equals the 57 The element is as a mixture also can be written as iron-57 of its isotopes and has an sum of protons + neutrons 26 Fe average mass as determined by a in the nucleus.
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C H E M I S T
Post-16 Induction C GCSE to A Level Chemistry - Bridging work - H Name : _______________________________ E M I ALL sections should be completed Bring this booklet to your first chemistry lesson in September. S T R Y 1 | P a g e INTRODUCTION Welcome to chemistry. In choosing to study chemistry you will develop many useful lifelong transferable skills, in addition to developing a deeper understanding of the subject. This booklet is designed to prepare you for your first year of study and hopefully answer some of the questions you may have at this stage. The first section gives some useful information about the subject, the details of your course, and gives you the opportunity to see course overview. You will typically have two chemistry teachers; (covering organic and inorganic modules), and lessons will take place in the Lycett building (GL0.02 to GL0.05). Contact me (subject leader) by e-mailing [email protected] over the summer if you have any questions. The second section (from page 6) is designed to review some of the work you will have covered at GCSE and make links with the new material you will cover in your first year of A-level chemistry. A lot of the material we cover in year 12 chemistry you will recognise from GCSE, however, we will build on, and extend your knowledge and understanding in each area. It would be advantageous for you to complete this booklet over the summer (use the answers at the back to self-mark) so that your subject knowledge is fresh when you start in the autumn.
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