1. Atomic Theory Zumdahl 2 p. 41-58

2. 1807 John Dalton All matter is made of atoms Atoms are indestructible and indivisible Atoms combine in small whole numbers to form compounds

3. Now Atoms are divisible Valence electron shell changes in chemical interactions

4. Questions How do atoms join to make compounds? Why do different atoms react in different ways?

5. Subatomic Particles ParticleRelative mass Relative charge Location Proton 1+nucleus Neutron 10nucleus Electron 1/1840- shells around nucleus

6. Perspective If the nucleus were 1 meter across, the electrons would be ten kilometers away. Most of an atom is empty space!

7. Atomic Number Atomic number (Z): number of protons Defines an element

8. Mass Number Mass number (A): protons + neutrons For light elements, protons = neutrons Heavier atoms require higher proportions of neutrons to overcome the repulsion between larger numbers of protons.

9. Isotope Notation Al-27 Aluminum-27

10. Neutral and Charged Neutral atom: electrons = protons Ion: an atom that has gained or lost electrons –Gained = - = anion –Lost = + = cation

11. Isotopes Isotope: atoms of the same element with different numbers of neutrons –different mass numbers –slightly different physical properties

12. Relative atomic mass Natural abundance: proportions of different isotopes of an element Used to determine relative atomic mass

13. Example For chlorine, 75% of atoms have a mass of 35, and 25% have a mass of 37. Relative atomic mass of chlorine is 35.5

14. Mixtures of Isotopes In nature, elements occur as a mixture of isotopes. Average atomic mass = weighted average of isotope masses On the periodic table, the average atomic mass is below the element name.

15. The Mass Spectrometer

16. Mass spectrometer: an instrument that separates particles by mass, and records the relative proportions of each size particle.

17. Use: to determine the natural abundances of the isotopes of a particular element and the atomic mass of an element. –More on how this works on Thursday!

18. Homework p. 76 #44, 46, 48, 50 p. 123 #22, 24 due Thursday Lab worksheet: Thursday Titration Research: Thursday Quiz (titration, one question): Thursday –see me for help on any of the above!