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Date Created: 09/18/14
CHEM 121 188 LECTURE NOTES DATE September 9 2014 THE ATOM Nucleus protons neutrons Parts of the Atom 1 Neutrons no N0 Charge 1 atomic mass unit u liz the mass of 0 Mass z 1 u 0 Found in the nucleus 12 one atom of C 0 Different number possible for same element 2 Protons p 0 1 charge 0 Mass z 1 u 0 Found in the nucleus 0 Define the element 0 Different number of p different element 3 Electrons e 0 1 charge 0 Mass z 0 0 Move around the nucleus Atomic Isotope Notation Element E Isotopes Variants of a particular element such that the element has the same number Mass number A p no of p but a different number of no Atomic number Z p Examples 12 C 13 C 6 6 Can also be Written as 12639 13639 Number of p 6 p 6 p Number of no 6 no 7 no This is because the amount of protons doesn t change only the amount of neutrons does A different number of protons gives you a different element Because isotopes have varying Weightsmasses the atomic Weightmass on the periodic table is a Weighted average based on the natural abundances of each element on Earth Natural abundances Examples 1 Carbon has an atomic Weight of 12011 gmol What are the relative abundances of 12C and 13 C Atomic Weight X isotope 1 y isotope 2 z isotope 3 12C 135 Mass 12 1300335 Fraction y X Here X y 1 After transposing We get y 1 X 12011 12 1 X X 1300335 12 12 X 1300335 X X 0011 0011100 11 13C 981 no The relative abundance of 12C is 981 While the relative abundance of 13C is 11 2 Bromine with an atomic Weight of 7990 gmol has only 2 stable isotopes One isotope of bromine present in 507 natural abundance has 44 neutrons in its nucleus What is the other stable isotope of Bromine We need to find the number of no Let this be equal to X 44 35 B7 x gB1 Massn p 4435z79 X35 Abundance 507 493 7990 050779 0493x 35 X 46 Mass number of the unknown isotope 46 35 81 The other stable isotope of Bromine is Br