Presentation on theme: "Atoms and the Periodic Table Part I: Historical Background."— Presentation transcript:
Atoms and the Periodic Table Part I: Historical Background
Current Atomic Theory 1.What makes up the atom? 2.Where are things found in the atom? 3.What kind of evidence lead to our current understanding of this theory?
History of Chemistry Practical Arts and Crafts (---to 600 B.C.E.) Greek Period (600 to 300 B.C. E.) Alchemy (300 B.C.E. to 1650 C.E.) Phlogiston (1650 to 1790) Modern Chemistry (1790--- ) Note: This listing focuses on the Middle East and Western Europe. Dates are very approximate.
Greeks and the Atom Leucippus and Democritus (ca 400 BCE) thought that matter was made up of tiny particles that could not be separated into smaller units. These particles were called atomos (uncuttable) Each atom had distinct shape and size.
Dalton’s Atomic Theory--1803 1.All matter consists of tiny indivisible and indestructible particles called atoms 2.Atoms of a given element are the same and have identical properties and masses. Atoms of different elements have different properties and masses
3. Atoms of different elements combine in small whole number ratios to form compounds 4. Chemical reactions involve rearranging atoms into new combinations.
If you remove electrons from an atom, you wind up with a positively charged “ion” Can do this by shooting a stream of electrons at atoms Resulting positive ions move toward negative electrode.
Goldstein used vacuum tube which had holes in the cathode Some positive particles were formed, moved toward the negative cathode and passed through the holes to hit the fluorescent screen Particles called “canal rays” (protons)