Chemistry 103OutlineStructure of the AtomAtoms: Composed of 3 Subatomic ParticlesAtomic SymbolsSlide 6Slide 7Atomic Symbol Notation vs. The Periodic Table NotationLearning CheckSlide 10Determine the number of subatomic particles for each:Exam type multiple choice questionHow Much Does an Atom Weigh?Atomic MassMass Number v. Atomic Weights/MassExamples of Isotopes and Atomic MassesCalculating Atomic MassCalculating an AverageSlide 19Slide 20Slide 21Isotopes of MagnesiumCalculating Atomic Mass of MgSlide 24Group Work: Average Atomic WeightsAtomic Mass CalculationChemistry 103Lecture 5Outline I. Review from last lecture II. Periodic Table–Atomic MassIII. Electronic StructureStructure of the Atom An atom consists•Of a nucleus that contains protons and neutrons•Of electrons in a large empty space around the nucleusCopyright © 2005 by Pearson Education, Inc.Publishing as Benjamin CummingsAtoms: Composed of 3 Subatomic ParticlesSymbol Relative Charge MassProton p or p+ +11.673x10-24gNeutron n or no 01.675x10-24gElectron e- -19.110x10-28gAtomic SymbolsXQAZMass number = number of protons + number of neutronsAtomic number = number of protonsDefines the elementCharge = Number of protons - number of electronsAtomic SymbolsXQAZMass number = number of protons + number of neutronsAtomic number = number of protonsCharge = number of protons – number of electronsAtomic SymbolsXQAZMass number = number of protons + number of neutronsAtomic number = number of protonsCharge = number of protons – number of electronsAtomic Symbol Notation vs. The Periodic Table NotationCa2+402020Ca40.078An atom of zinc has a mass number of 65.1. How many protons are in this zinc atom? A) 30 B) 35 C) 652. How many neutrons are in the zinc atom? A) 30 B) 35 C) 653. What is the mass number of a zinc atom that has 37 neutrons? A) 37 B) 65 C) 67Learning Check10Write the nuclear symbols for atoms with the following subatomic particles: 47p+, 60 n, 47 e-___________ 12p+, 12n, 10e- ___________ Learning CheckDetermine the number of subatomic particles for each:•Co-59•Pb Z = 82 A = 207•39K+•19F-Exam type multiple choice question•The radioactive isotope strontium-90, a component of fallout from atmospheric nuclear testing, is particularly hazardous because its 2+ ion may substitute for that of calcium in bone. 90Sr2+ has•a. 38 protons, 52 neutrons, and 36 electrons•b. 38 protons, 52 neutrons, and 38 electrons•c. 38 protons, 52 neutrons, and 40 electrons•d. 52 protons, 38 neutrons, and 50 electrons•e. 52 protons, 38 neutrons, and 54 electronsHow Much Does an Atom Weigh?•The mass of atoms is measured in units of amu–atomic mass unit•Defined as 1/12th the mass of 12C Therefore, C-12 is exactly 12 amu on this scale•Masses reported on the periodic table are weighted averages•Takes into account the fact that element samples consist of mixtures of different isotopes14Atomic MassThe atomic mass of an element,•Is listed below the symbol of each element on the periodic table•Gives the mass of an “average” atom of each element compared to 12C •Is not the same as the mass numberNa22.99Mass Number v. Atomic Weights/Mass20Ca40.078•Mass Number = the number of protons plus the number of neutrons•ALWAYS A WHOLE NUMBER•NOT FOUND ON THE PERIODIC TABLE!•Atomic Weight/Mass = the mass of an average atom•Found on the Periodic Table•An average of the masses of all the isotopes of an element16Examples of Isotopes and Atomic MassesMost elements have two or more isotopes that contribute to the atomic mass of that element.17Calculating Atomic MassThe calculation for atomic mass requires the:•Percent (%) abundance of each isotope•Atomic mass of each isotope of that element•Sum of the weighted averages mass isotope1(%) + mass isotope2(%) + … 100 100Calculating an Average•Exam Scores (10 students): •95, 85, 85, 82, 79, 79, 79, 79, 65, 51•How do you determine an average?Calculating an Average•Exam Scores (10 students): •95, 85, 85, 82, 79, 79, 79, 79, 65, 51 95+85+85+82+79+79+79+79+65+51 = 77.9 10Calculating an Average•Exam Scores: •95, 85, 85, 82, 79, 79, 79, 79, 65, 51•95+85+85+82+79+79+79+79+65+51 = 77.9 10Alternate way of writing:•95+(85 x 2)+82+(79 x 4)+65+51 = 77.9 10Calculating an Average•Exam Scores: •95, 85, 85, 82, 79, 79, 79, 79, 65, 51•10% = 95, 1/10 x 100% = 10%•20% = 85, 2/10 x 100% = 20% etc….•Total percentages = 100%Weighting factor:(95 x 0.1)+(85 x 0.2)+(82 x 0.1)+(79 x 0.4)+(65 x 0.1)+(51 x 0.1) = 77.922Isotopes of MagnesiumIn naturally occurring magnesium, there are three isotopes. 24Mg 25Mg 26Mg 12 12 1223Calculating Atomic Mass of MgIsotopes Mass of Isotope Abundance Weighted portion 24Mg = 23.985 amu x 78.70/100 =18.88 amu 25Mg = 24.986 amu x 10.13/100 = 2.531 amu 26Mg = 25.983 amu x 11.17/100 = 2.902 amuAtomic mass (average mass) Mg = 24.31 amu Mg24.3124Calculating Atomic Mass of MgIsotopes Mass of Isotope Abundance Weighted portion 24Mg = 23.985 amu x .7870 = 18.88 amu 25Mg = 24.986 amu x .1013 = 2.531 amu 26Mg = 25.983 amu x .1117 = 2.902 amuAtomic mass (average mass) Mg = 24.31 amu Mg24.31Group Work:Average Atomic Weights•Naturally occurring carbon is composed of 98.93% 12C and 1.07% 13C. If the mass of one 12C atom is 12 amu and the mass of one 13C atom is 13.00335 amu, what is the average mass of naturally occurring carbon?Atomic Mass Calculation•Naturally occurring sulfur consists of 4 isotopes – calculate the atomic mass of SSulfur Isotopes Atomic Mass % Abundance 31.9721 95.0% 32.9715 0.76% 33.9679 4.22% 35.9671