1. Isotopes & Average Atomic Mass

2. Why…. do these atomic masses have so many decimal points? 11 Na Sodium 22.9897 17 Cl Chlorine 35.4527 ISOTOPES!

3. Definitions element isotope Isotopes- elements with the same number of protons, but different numbers of neutrons. The Proton number determines the ___________. The Neutron number determines the ___________.

4. …one more definition. the weighted average of the atomic masses of the naturally occurring isotopes of an element. Average Atomic Mass:

6. 1 2 Brown Horse Brown Horse 12% 13% 3 4 Brown Horse Brown Horse 20% 55%

7. 1 sock(.12)+2 sock(.13)+3 sock(.20)+4 sock(.55) = Average 2.98 socks on brown horses.

8. Lets apply this to the elements 17 Cl Chlorine 35.4527

9. Chlorine Isotopes 35Cl What is the mass of 35Cl ? It’s abundance on earth is 75.77% 37Cl How much does 37Cl weigh? It’s abundance on earth is 24.23%

10. Cl Average Atomic Mass: 35(75.77) + 37(24.23) = 100 or 35(.7577) + 37(.2423)=

11. Hydrogen Isotopes

12. Hydrogen 1 (protium):“Normal” form of hydrogen: safe, standard element found in majority of bonds in the universe. Hydrogen 2 (deuterium):can form “heavy water” which is toxic to people. Sometimes used as a tracer molecule in biochemistry because it behaves chemically like H-1 Which Isotope is most abundant? How do you know? Hydrogen 3 (tritium):Radioactive isotope. Only dangerous if ingested or inhaled. Produced naturally in the upper atmosphere when cosmic rays strike air molecules. Also produced during nuclear weapons explosions, & as a byproduct in reactors producing electricity.Used in self-powered lighting, such as watches and exit signs in planes.