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

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

3. Location
How are they different?
Mass
Charge

4. Mass on Ar scale
Charge p 1 +1 n e- -1

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

6. Cl Cl What are isotopes? p? p? e-? e-? n? n? 17 17 17 17 18 2035 37
e-?
e-? 17 17 18 20 n? n?
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 35Cl O.K.? Cl Cl Cl-37 Cl-35 Relative isotopic mass
Chlorine always
has an atomic
number of 17!
Relative isotopic mass Cl Cl 37 35 17 17
Cl-37
Cl-35

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

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

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

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

12. Mass spectrometry

14. Mg+ Mg e- e-

15. Cl-35
Cl-37

16. A mass spectrum …
100 80 60 % 40 20
mass 35 36 37

17. A mass spectrum …
Try W and Y!
100 80 60 % 40 20
mass 24 25 26