1. Atomic Theory and Structure of the Atom

2. first to suggest the existence of atoms believed atoms were small indivisible particles Atom: smallest particle of an element that retains all properties of the element. A. Democritus (460 B.C. – 370 B.C)

3. B. Dalton Atomic theory composed of 4 postulates – Elements are composed of atoms – Atoms of the same element are identical, each element is unique – Compounds are composed of atoms of more than 1 element, atoms combine in fixed ratios to form compounds – Chemical rxn involves separation, combination, or rearrangement of atoms Name of theory Billard Ball Model

4. C. Electron 1.Symbol: e − – Charge −1 **after Dalton, there was a big hiatus in the theory of the atom. Everyone accepted Daltons theory and went on to study radiation for a while, and this is when the electron was discovered

5. D. J.J. Thomson An atom is thought of as a uniform positive sphere with electrons evenly distributed through out (like plum pudding or a chocolate chip cookie) Name of theory Plum Pudding Model

6. Cathode Ray Tube Battery Evacuated tube Cathode Anode − +

7. E. Millikan Millikan Oil Drop Found the mass of an electron to be 9.10×10 −28 g

8. F. Rutherford Conducted gold foil experiment

9. What did Rutherford expect? Gold Foil Experiment Animation and Discussion Click here for video!

10. What did Rutherford actually see?

11. F. Rutherford Concluded all positive charge and mass is concentrated in small region called nucleus and the electrons are outside the nucleus Proposed atom is mostly empty space Name of theory Nuclear Model Proton – p + – Charge: +1 – Mass:1.673×10 −24 g

12. G. Bohr Expanded on the nuclear atom Electrons travel in circular orbits around the nucleus Name of theory Planetary Model

13. H. Schrödinger model allowed the electron to occupy three-dimensional space like an electron “cloud” Name of theory Quantum Mechanical Model or Electron Cloud Model

14. I. Chadwick The Neutron Symbol: n 0 Charge: none Mass:1.675×10 −24 g **The neutron was found by comparing the mass of hydrogen to helium, since He increased by 1proton, the mass should be double, but it was four times, leading to a subatomic particle that had mass but no charge.

15. Fun Facts The volume of a hydrogen nucleus is a trillion times smaller than the volume of a hydrogen atom, yet the nucleus contains most of the mass. If the nucleus (proton) of a hydrogen atom were as large as the width of a human thumb, the electron would be on the average about one kilometer away in a great expanse of empty space.