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Download PowerPoint - Significant Digits in Calculations, Isotopes
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Transcript
Isotopic Abundance Reminder: bring a calculator to class Isotopes & Radioisotopes • Isotopes have same number of protons (atomic #) and different numbers of neutrons and therefore different masses • Isotopic abundance is the percentage of a given isotope in a sample of an element. • Mass spectrometer is used to determine the mass and abundance of isotopes • Radioisotopes are isotopes that have unstable nucleus and undergo radioactive decay. • Radioactive decay is the spontaneous disintegration of unstable isotopes to emit nuclear radiation such as alpha particle, beta particle and gamma ray Nuclear radiation • Particles emitted from nucleus of radioisotopes • Alpha particle – a positively charged particle with the same structure as the nucleus of a helium atom • Beta particle – a negatively charged particle identical to an electron • Gamma ray – a high-energy electromagnetic radiation Isotopic abundance • Let’s consider the following question: if 12C makes up 98.89% of C, and 13C is 1.11%, calculate the average atomic mass of C: Mass from 12C atoms 12 x 0.9889 11.8668 + Mass from 13C atoms + 13 x 0.0111 + 0.1443 = 12.01 Mass from 35Cl + Mass from 37Cl 35 x 0.7553 + 37 x 0.2447 26.4355 + 9.0539 = 35.49 Mass from 39K 39 x 0.9310 36.309 + Mass from 41K + 41 x 0.0690 + 2.829 = 39.14 Mass from 40Ar + Mass from 36Ar + Mass from 38Ar 40 x 0.9960 + 36 x 0.0034 + 38 x 0.0006 + 0.0228 39.84 + 0.1224 = 39.99