1. Chemical Ideas 2.1. A simple model of the atom.

2. What’s inside? In the nucleus? Protons And around the nucleus? Electrons Neutrons

3. How are they different? Mass Charge Location

4. Mass on Ar scale Charge p1+1 n10 e-e- 0.00055

5. Nuclear symbols Na 23 11 Mass number =? Atomic number =? p + n p ( = e - ) p? e-?e-? n? 11 12

6. What are isotopes? Cl 35 17 Cl 37 17 p? e-?e-? n? p? e-?e-? n? 17 1820 17 Atoms of the same element with: The same atomic number but different mass numbers Same number of protons but different numbers of neutrons

7. Why is 35 Cl O.K.? Cl 35 17 Cl 37 17 Relative isotopic mass Cl-35 Cl-37 Chlorine always has an atomic number of 17!

8. So what is relative atomic mass? Cl-35 Cl-37 75% 25%

9. Relative atomic mass is the average of the relative isotopic masses Cl-35 Cl-37 75% 25% How do we get a relative atomic mass of 35.5?

10. What 2 things did we need to know? Relative isotopic masses. The relative abundances.

11. How do we find them out? Use a mass spectromete r

12. Mass spectrometry

14. Mg e-e- e-e- Mg +

15. Cl-35 Cl-37

16. A mass spectrum … 35 3736 20 40 60 80 100 % mass

17. A mass spectrum … 24 2625 20 40 60 80 100 % mass Try W and Y!