1. Atomic Theory Ancient and Modern

2. Ancient Theory D e m o c r i t u s Greek philosopher/scientist Stated that everything is made up of “void” in which exists infinite, tiny, indivisible particles “Atom” comes from Gr. “atomon,” meaning “indivisible”

3. John Dalton (1766-1844) 5 basic postulates: 1.All matter consists of tiny particles called atoms 2.Atoms are indestructible and unchangeable 3.All atoms of the same element have the same weight, and all atoms of different elements have different weights* 4.Atoms in reactions combine in simple, whole- number ratios (Law of Definite Proportions) 5.Sometimes atoms combine in more than one simple, whole-number ratio *We now say that atoms of the same element have the same “nuclear charge”

4. J.J. Thomson (1856-1940) “Cathode ray” (stream of electrons) experiment “Plum-pudding” model of the atom Mass-to-charge ratio of electron J.J. Thomson’s cathode ray apparatus—the negatively-charged “cathode rays” (electrons) are attracted to the positively-charged plate

5. Ernest Rutherford (1871-1937) Discovered nucleus with gold foil experiment Shot He atoms at a piece of gold foil surrounded by radioactive Zn—if plum- pudding model was correct, atoms should go straight through Found that some atoms ricocheted! Concluded that atoms have a dense, positive core (nucleus)

6. Rutherford’s Experiment

7. Looked at light emitted by heated materials Came up with an equation that related energy emitted to the frequency of light emitted E=h f h=constant (6.626 x 10 - 34 J s) f=frequency (Hz) E=energy (J) Discovered that energy can only be emitted in discrete packets, called “quanta” (sing. “quantum”) Max Planck (1858-1947)

8. Niels Bohr (1885-1962) Postulated that atoms have different energy levels Theorized that electrons can absorb photons of light and “jump” from one energy level to the next When electrons fall back, they emit photons of light H atom Energy level 43214321 Whee!!

9. Quantum Theories Each electron in an atom has 4 quantum numbers to define position and properties: 1) 1) Principal quantum number (n)—describes e - energy level: n=1,2,3… 2) 2) Angular momentum quantum number ( l )—describes orbital: l =0 for s, 1 for p, 2 for d, etc. 3) 3) Magnetic quantum number (m l )—describes position (i.e. which “box” in orbital diagrams): m l = - l to + l 4) 4) Spin quantum number (m s )—describes movement: -½, +½ Pauli Exclusion Principle : no two electrons can have the same 4 quantum numbers

10. More Quantum Stuff D orbital: n=3, l =2 S orbital: n=1, l =0 m l =0 P orbital: n=2, l =1 m l =0 m l =-1m l =1 S orbital: n=2, l =0 P orbital: n=3, l =1 S orbital: n=2, l =0 Chromium orbital-filling diagram n=3, l =2, m l =-2, m s =+½

11. Yet More Quantum Stuff Albert Einstein (1879-1955): Light has properties of both particles and waves. Louis de Broglie (1892-1987): Matter has wave- like properties. Heisenberg Uncertainty Principle: It is impossible to know both speed and position of an electron at the same time.

12. www.britannica.com/ nobel/cap/oruthef002a4.html http://www.bookrags.com/sciences/chemistry/atomic- theory-woc.html Bibliography