1. Relative Atomic Mass Mass of atoms is incredibly small! So we have to use relative atomic mass. The symbol for relative atomic mass is Ar Carbon- 12 atom contains 6 protons, 6 neutrons and 6 elections. Its relative atomic mass is defined as exactly 12. Every other atom is compared to this. E.g Helium is one 3 rd of a carbon atom. So its relative atomic mass is 4.

2. Calculate the relative atomic masses of an element using masses and abundance (A/A*) The relative atomic mass of bromine is 80 This is because in any sample of bromine, there are just about equal numbers of its two isotopes 79Br and 81Br. So the ‘average’ bromine atom has a relative mass of 80.

3. What about Chlorine and Copper? Chlorine has two isotopes Copper has two main isotopes Chlorine 3575% 3725% Copper 6369% 6531%

4. Finding the RAM of Chlorine If you assume you have 100 atoms then the average is easier to find. 35 37 35 37 35 37 35

5. Finding the RAM of Chlorine You have 75 atoms of chlorine-35 and 25 atoms of chlorine-37 35 37 35

6. Finding the RAM of Chlorine That’s a mass of 75 x 35 and 25 x 37 To give the mass of the 100 atoms 35 37 35

7. Using Weighted Averages So the average mass of a chlorine atom isn’t (35+37)/2 Its (35 x 75) + (37 x 25) 100 35 37 35

8. From Weighted Averages to RAM Weighted = ( mass x number ) + ( mass x number ) ave total number So RAM = (35 x 75) + (37 x 25) 100 RAM = (2625 + 925)/100 RAM = 35.5 amu

9. Weighted Averages Use RAM = (mass no x %) + (mass no x %) 100 To work out the RAM of Copper

10. RAM of copper RAM = (mass no x %) + (mass no x %) 100 So RAM = (63 x 69) + (65 x 31) 100 RAM = (4347 + 2015)/100 RAM = 63.6 amu

11. Here are various Isotopes- Attempt to calculate the number of electrons neutrons and protons for each. C – 12 C- 14 He – 4 He- 5 Li – 7 Li- 6

12. Isotopes Isotopes are atoms of the same element with different numbers of neutrons. That is; Same Atomic Number Same no. of protons Different Mass Number Different no. of neutrons Define an isotope in your own words before your see my definition

13. http://www.youtube.com/watch?v=EboWeWmh5Pg Watch the clip and answer the questions!

14. Isotopes of hydrogen IsotopeSymbolPNE Protium 101 Used as fuel, for hardening margarine. Deuteriu m 111 Used in heavy or deuterated water, solvent Tritium 121 Radioactive, Used in H-bombs, glow in the dark paints

15. Isotopes of hydrogen ProtiumDeuterium Tritium 1 proton, 0 neutron, 1 electron 1 proton, 1 neutron, 1 electron 1 proton, 2 neutron, 1 electron

16. Isotopes Element Symbo l Mass No Atomic No ProtonsNeutrons Electron s Chlorine-35Cl3517 Chlorine-37Cl3717 Copper-63Cu6329 Copper-65Cu6529 Bromine-79Br7935 Bromine-81Br8135 Objective check -