Presentation on theme: "What is atomic mass? Also referred to as:"— Presentation transcript:
1 What is atomic mass? Also referred to as: Atomic weightAverage atomic massRelative atomic massImportant characteristic for elements:Each element has its own atomic massAtomic mass is an averageAverage of the masses of a number of different atomsSpecial kind of average called a weighted averageDifferent than the usual average you’re probably familiar with in mathAtomic mass
2 Understanding Weighted Averages Even though these are different models and have different features, they are both lemonas due to their distinct lemon-like shapeUsing this analogy, the models of the lemona are similar to the isotopes of an element29 protons makes both atoms copper—even though they differ in their numbers of neutronsJust like the “lemon-like” shape of a car makes it a lemona—even though they differ in their features
3 Average vs. Weighted Average What is the average weight of the 2 cars?4,000+5,000 2 =4,500Regular AverageWhat would happen if we added in extra information?
4 Weighted AverageWhat is the average weight of lemonas, taking into account the amount of each model? 4,000 𝑥 .95 +(5,000 𝑥 .05)=4,050 𝑙𝑏𝑠Because there are so many more GXs than GXLs, the weighted average is much closer to the actual weight of a lemona GX
5 Using Weighted Average with Different Atoms Atomic mass: a weighted average of the masses for all the isotopes of a certain elementMass = 63 amuMass = 65 amuIf we pulled out a random sample of 100 copper atoms, we would find that 69% of them would be Cu-63 and 31% of them would be Cu-6569% : Cu-6331% : Cu-65
6 Atomic Mass of Copper 63 𝑥 .69 + 65 𝑥 .31 =63.62 𝑎𝑚𝑢 69% : Cu-63 Why are the 2 atomic masses different then?
7 Difference between mass number and atomic mass Mass number: protons + neutrons1 proton or 1 neutron = 1 amuTherefore, if you have 6 protons and 6 neutrons, your atom is going to weigh 12 amuIf you have 6 protons and 7 neutrons, your atom is going to weight 13 amu
8 PracticeGallium has 2 stable isotopes, and the masses of Gallium-69 (60.11% abundant) and Gallium-71 (39.89% abundant) are amu and amu, respectively. Calculate the average atomic mass of Gallium
9 PracticeRubidium has 2 isotopes: Rubidium-85 (atomic mass of amu) and Rubidium-87 (atomic mass of amu). The atomic mass of Rubidium reported on the periodic table is amu. Based on this information, which of the isotopes of Rubidium is more abundant? How do you know?This is more of a thought problem. No real calculations are really necessary
10 PracticeMagnesium has 3 stable isotopes. Calculate its average atomic mass, using the information in the chart below.IsotopeMassAbundanceMg-24amu78.99 %Mg-25amu10.00 %Mg-26amu11.01 %