Calculating Atomic Mass - Unit 2 Day 4 PDF

D ay 4 - Note s Unit: Atomic Structure Atomic Mass Units (amu) and Calculating Atomic Mass Copyrig...

D ay 4 - Note s Unit: Atomic Structure Atomic Mass Units (amu) and Calculating Atomic Mass Copyright © 2015 - MsRazz ChemClass  After today, you should be able to… Calculate the atomic mass when provided with percent abundances and atomic masses of isotopes Compare the relative abundance of isotopes for a particular element Copyright © 2015 - MsRazz ChemClass  Remember??? Mass number = protons + neutrons Isotopes= atoms with different # of neutrons Atomic masses occur with decimal points because they are an average of different isotopes Copyright © 2015 - MsRazz ChemClass  Atomic Mass Units Defined as 1/12 the mass of a Carbon-12 atom. The way that atomic mass is measured on the Periodic Table Abbreviated “amu” Copyright © 2015 - MsRazz ChemClass  To find the atomic mass, you need to know: Number of stable isotopes Mass of each isotope Natural % abundance of each isotope Copyright © 2015 - MsRazz ChemClass  Real-World Application: Weighted Average Let’s pretend that the category percentages that make up your grade are as follows: Tests – 70% of grade Quizzes – 20 % of grade Homework –10% of grade You earn the following grades: test – 80, quiz – 100, homework – 100 Copyright © 2015 - MsRazz ChemClass  To Find Weighted Average… Final Grade = (.7)(80)+(.2)(100)+(.1)(100) 56 + 20 + 10 = 86% Don’t forget! All percentages must = 100% All decimals = 1 Copyright © 2015 - MsRazz ChemClass  To Calculate Atomic Mass : %1 %2 Atomic mass 1 + Atomic mass 2 +⋯ 100 100 Copyright © 2015 - MsRazz ChemClass  Example - Chlorine Calculate the atomic mass of chlorine if the two common isotopes of chlorine have masses of 35.45 amu (75.00% abundance) and 37.29 amu (25.00% abundance). Copyright © 2015 - MsRazz ChemClass  Atomic Mass of Chlorine a.m.= 35.45amu a.m.=37.29amu %1= 75.00% %2= 25.00% (35.45amu)(.7500) + (37.29amu)(.2500) 26.59 amu + 9.323 amu Atomic mass of Chlorine= 35.91 amu Copyright © 2015 - MsRazz ChemClass  What if you don’t have the percentage or the atomic mass? Calculate the atomic mass of one of indium’s isotopes (there are two) if the atomic mass of indium is 114.8200 amu and one isotope of indium has a mass of 114.9041 amu and an abundance of 95.795%. Copyright © 2015 - MsRazz ChemClass  a.m. of indium=114.8200amu a.m.= 114.9041amu a.m.= ? %1= 95.795% %2= ?100-95.795= 4.205% 114.8200amu = (114.9041amu)(0.95795)+(x)(0.04205) 114.8200amu = 110.07 + (x)*(0.04205) -110.07 -110.07 4.75 = 0.04205x 0.04205 0.04205 Atomic mass of Indium= 113 amu Copyright © 2015 - MsRazz ChemClass  Questions? Begin Worksheet # 4 Copyright © 2015 - MsRazz ChemClass