2. Isotopes are atoms of the same element that have a different number of neutrons For example, Hydrogen has 3 isotopes: Protium (0 neutrons) Deuterium (1 neutron) Tritium (2 neutrons) Isotopes

3. Atomic mass (the number found under the chemical symbol on the periodic table) is the average mass of one mole of those particular atoms. It’s an average mass, because it takes into account all the known isotopes of that element and their relative abundances (weighted average). Relative abundance is just the percentage of each isotope found on earth Relative abundance of Hydrogen: Hydrogen-1: 99.99% Hydrogen-2: 0.015% Hydrogen-3: ~0.00001% Atomic Mass

4. No! The mass number is the number of protons + neutrons in a particular isotope Ex. Hydrogen-1, Hydrogen -2, & Hydrogen-3 weighted average The atomic mass is a weighted average of the mass numbers of all the isotopes for an element Ex. The mass of hydrogen-1, hydrogen-2, & hydrogen-3 are averaged together to give the atomic mass 1.008 amu. IS THE ATOMIC MASS AND MASS NUMBER THE SAME THING?

5. Your final grade is a weighted average. 40% is based on your 1 st qtr grade 40% is based on your 2 nd qtr grade 20% is based on your final exam grade What counts most toward your final grade? What is a weighted average?

6. The isotope that is most abundant in nature contributes most to the overall atomic mass on the periodic table Ex. Hydrogen-1 has an abundance of 99.985% Hydrogen-2 has an abundance of 0.015% Hydrogen-3 has an abundance of ~0.00001% Which isotope of hydrogen has a bigger impact on the overall atomic mass? Weighted averages and isotopes

7. Take the percentage of each isotope and change it to a decimal (move decimal point two places to the left) Multiply each decimal by the mass given of that particular isotope Add these answers together Cl-35 = 76% 35 X.76 = 26.6 amu Cl-37 = 24%37 X.24 = 8.9 amu 35.5 amu Calculating Atomic Mass

8. The element copper has naturally occurring isotopes with mass numbers 63 and 65. The relative abundance and atomic masses are 69.2% for mass=62.93 amu, and 30.8% for mass=64.93 amu. Calculate the atomic mass of copper EXAMPLES

9. Calculate the atomic mass of bromine. The two isotopes of bromine have atomic masses and relative abundance of 78.92 amu (50.69%) and 80.92 amu (49.31%) Learning Check

10. Element X has two natural isotopes. The isotope with a mass of 10.012 amu has a relative abundance of 19.91%. The isotope with a mass of 11.009 amu has a relative abundance of 80.09%. Calculate the atomic mass of this element. Learning Check