1. 1 The Atom, in a nutshell…

2. 2 Democritus (c. 460—370 BC) Greek philosopher  The name atom was his idea  Proposed matter is made up of small particles  Atoms comes from atomos=indivisible  Atoms differ in size and shape and combine in different ways, & constantly moving

3. 3 John Dalton (1766—1844) English chemist & physicist, self educated published Atomic Theory: 1.Each element made of really small particles called atoms 2.All atoms of a given element are identical 3.Atoms of different elements have different properties, like mass and chemical reactivity 4.Atoms aren’t changed by chemical reactions, just rearranged

4. 4 J.J. Thomson (1856—1940)  Identified the electron using cathode ray tube, determined negative charge  Atom is neutral, with a positive sphere and negative electrons embedded called the “plum pudding” model. Yum.  The television and computer monitors use this technology even today.

5. 5 Ernest Rutherford (1871—1937) Gold Foil Experiment—bombarded gold foil with radioactive particles, most passed through, some bounced back! Conclusions:  Some parts of atom must be more dense.  New picture of the atom: dense at the center, electrons on the outside  Atom mostly empty space, most of mass found in the center—nucleus with positively charged protons Hyperlink to demo

6. 6 Niels Bohr (1885—1962)  Used light and observed the way light interacts only with specific energies: determined the electrons are in specific levels  Electrons moving around nucleus in fixed orbits w/fixed energy  Sometimes called the planetary model  Not completely accurate with how electrons are truly arranged

7. 7 Other Scientists  Louis de Broglie (1892—1987): mathematical description of electrons in atoms  James Chadwick (1891—1974): discovered the neutron around 1932, another massive particle in the nucleus

8. 8 Basics on the atom:  Three kinds of subatomic particles are electrons, protons, and neutrons.  The nucleus is the center area of an atom and contains most of its mass  Protons and neutrons are found in the nucleus. Each has a mass of 1 amu  Electrons are found in levels outside of the nucleus

9. 9 Summary of particles

10. 10 The number of protons are equal to the number of electrons in an atom so… Put a number where there is a letter.

11. 11 Answers: 19 All of the numbers have to be the SAME!

12. 12 Answers: B55 19 16 23

13. 13 Finding the amount of neutrons is a bit more work… Li 7 3 This is called the isotope notation.

14. 14 The notation means: Li 7 3 Mass number, A Protons and neutrons added together Atomic number, Z Number of protons only 7 3 4 This particular atom has 4 neutrons. Lithium - 7

15. 15 The notation means: Li 6 3 Mass number Protons and neutrons added together Atomic number Number of protons only 6 3 3 This particular atom has 3 neutrons. Lithium - 6

16. 16 Li 6 3 7 3 Both of these atoms would have the same chemical properties, but one is slightly heavier than the other. They are Isotopes.

17. 17 Hint: always find the atomic number FIRST then make protons and electrons equal to that!

18. 18 9 9 Neutrons = mass – atomic [ ] = ? – [ ]

19. 19 9 9 Neutrons = mass – atomic [ 10 ] = ? - [ 9 ] What does the “?” equal?

20. 20 9 9 F 19

21. 21 9 9 F 19 29 14 Si 22 25 Ti Mn25 30 25

22. 22 Other demos - Link: Fun facts about atomic particles Modern view of atom: