1. Isotopes and abundance

2. The relative atomic mass scale is now based on an isotope of carbon, carbon-12, which is given the value of 12.0000 amu.

3. CHARACTERISTICS OF ELECTRON Charge: It is a negatively charged particle. Mass of electron: Mass of electron is 0.000548597 a.m.u. or 9.1 x 10 -31 kg. CHARACTERISTICS OF PROTON Charge: Proton is a positively charged particle. Mass of proton: Mass of proton is 1.0072766 a.m.u. or 1.6726 x 10 -27 kg. Comparative mass: Proton is 1837 times heavier than an electron. CHARACTERISTICS OF NEUTRON charge: It is a neutral particle because it has no charge. Mass of neutron:. Mass of neutron is 1.0086654 a.m.u. or 1.6749 x 10 -27 kg. Comparative mass: Neutron is 1842 times heavier than an electron.

4. A r = RAM

5. Isotopes are atoms of the same element with different masses due to different numbers of neutrons.. For example, and are the three The symbol of the Isotope tells us the number of protons All Isotopes of H have 1 proton

6. Abundance To calculate RAM from isotopic masses use RAM = (Mass1 x %1) + (Mass2 x %2) + (Mass 3 x %3)

7. Ave =Total value # of coins = 150/ 10 = 15 c

8. Ave =Total value # of coins = 110/ 10 = 11 c

9. Ave =Total value # of coins = 210/ 10 = 21 c

10. To calculate RAM from isotopic masses use RAM = (M 1 x %1) + (M 2 x %2) + (M 3 x %3)

11. Example 1.1: Bromine consists of 50% 79 Br and 50% 81 Br, calculate the Ar of bromine. RAM = (M 1 x %1) + (M 2 x %2) + (M 3 x %3)

12. Second example if needed Example 2: Chlorine consists of 75% Chlorine-35 and 25% Chlorine-37. RAM = [ (75 x 35) + (25 x 37) ] / 100 = 35.5 So the relative atomic mass (RAM) for chlorine is 35.5 or or A r (Cl) = 35.5

13. W W W We Do Neon has a two isotopes Ne-20 and Ne 22 they have abundances of 80% and 20% respectively. Calculate the RAM for Neon

14. NOW It’s your turn