1. Science Starter: Black Boxes Groups of 2: Manipulate the box so the marble moves around the fixed object inside of the box. DO NOT OPEN THE BOX Discuss what the object in the box might look like. On the science starter page, sketch the object in the box, showing its size, shape and location within the box. Time for Activity: 10 minutes

2. Thomson’s Atomic Model Thomson: electrons were like plums embedded in a positively charged “pudding” the “plum pudding” model J. J. Thomson

3. Ernest Rutherford’s Gold Foil Experiment - 1911  Alpha particles (helium nuclei) were fired at a thin sheet of gold foil  Particles that hit on the detecting screen (film) are recorded

4. Rutherford’s Findings a) The nucleus is small b) It is dense c) It is positively charged  Most of the particles passed right through  A few particles were deflected  VERY FEW were greatly deflected “Like howitzer shells bouncing off of tissue paper!” Conclusions:

5. The Rutherford Atomic Model Based on his experimental evidence: –The atom is mostly empty space –All the positive charge, and almost all the mass, is in the center “nucleus” –The nucleus is composed of protons and neutrons –The electrons are distributed around the nucleus and occupy most of the volume “nuclear model”

6. Section 4.3 Distinguishing Among Atoms

7. Atomic Number Atoms are composed of identical protons, neutrons, and electrons Elements are different because they contain different numbers of PROTONS The “atomic number” of an element is the number of protons in the nucleus # protons in an atom = # electrons

8. Element # of protons Atomic # (Z) Carbon66 Phosphorus1515 Gold7979 Look at the periodic table to confirm these numbers

9. Mass Number Mass number is the number of protons and neutrons in the nucleus of an isotope: Mass # = p + + n 0 Nuclide p+p+p+p+ n0n0n0n0 e-e-e-e- Mass # Oxygen - 10 -3342 - 31 - 3115 8 8 18 Arsenic 7533 75 Phosphorus 15 31 16 This mass # may not match the mass # on the periodic table

10. Complete Symbols Include the symbol of the element, the mass number and the atomic number. X Mass number Atomic number Subscript → Superscript →

11. Symbols n Find each of these: a) number of protons b) number of neutrons c) number of electrons d) Atomic number e) Mass Number Br 80 35