1. Isotopes and Average Atomic Mass Chemistry 11

2. Page 839 1.Precise (1.5%) but not accurate (32%) 2.Systematic (instrument calibration) 3.Capacitance dilatometer (elevator, door) 4.Bathroom scale 5.a) plus or minus.05s b) Yes, 50% difference

3. Page 840 a)101.5g b)2.5mm c)1.698L d)3.07mL e)35.2cm 2 f)8.0g/cm 3

4. Isotopes The number of protons define the type of atom: –6 protons is carbon –1 proton is hydrogen –8 protons is oxygen –92 protons is uranium However the number of neutrons can vary within a given type of atom

5. Hydrogen Isotopes There are three main isotopes of hydrogen –Hydrogen – 1p, 0n, 1e –Deuterium – 1p, 1n, 1e –Tritium – 1p, 2n, 1e

6. Relative Mass of an Atom The mass of an atom is expressed in atomic mass units (u) Atomic mass is determined based upon carbon-12 as a standard with a mass exactly equal to 12u Using this, the relative mass of every atom on the periodic table can be determined (i.e. oxygen 16 would have a mass of 16u)

7. Isotopic Abundance Because elements as a combination of different isotopes, it is useful to consider the isotopic abundance For example, magnesium is composed of: –Magnesium-24 – 79% –Magnesium-25 – 10% –Magnesium-26 – 11% Regardless of where you find magnesium, it will be composed of these percentages

8. Average Atomic Mass and the Periodic Table The average atomic mass that appears on the periodic table is the average of the mass of all the element’s isotopes Therefore, even carbon, which is used as the standard, does not have an average atomic mass of 12 but rather 12.01 due to the presence of carbon-14 Carbon-14 is about 1.1% of all carbon while carbon-12 is the remaining 98.1%

9. Average Atomic Mass Calculation

10. Average Atomic Mass Naturally occuring silver exists as two isotopes. From the mass of each isotope and the isotopic abundance listed below, calculate the average atomic mass of silver IsotopeAtomic mass (u)Abundance (%) Silver-107106.951.8 Silver-109108.948.2

11. Average Atomic Mass

12. Questions Page 45 –Questions 1-4 Page 46 –Questions 1-6