Early Modern Atomic Theory History
Aristotle’s theory- all matter can be grouped into four main elements, fire, water, air, and earth
- matter can be part of multiple elements. EX: a Rabbit is air, water, and fire (Life)
Democritus’s idea- all matter is made up of tiny, indestructible particles called atoms
- he didn’t have any experimental evidence though, so people continued to believe Aristotle instead
Alchemy- both a philosophy and a hunt for ways to turn lead (or another common material) into gold so the alchemists could be closer to God.
- although their philosophy was wrong, they developed and used the scientific method and a lot of the lab techniques that we still use today
Law of conservation of matter- matter is neither created nor destroyed
Law of definite proportions- a given chemical compound always contains its component elements in fixed ratio and does not depend on its source and method of preparation.
John Dalton: had five main theories
- matter is composed of tiny particles called atoms
- atoms are fundamental, indestructible, and indivisible particles
- all atoms of a given atom are exactly alike
- atoms of one element cannot change into another element, but they can combine in simple whole ratios to make compounds
- In a chemical reaction, atoms are separated, combined, or rearranged
Theory 2 is partially incorrect because Atoms actually are divisible. Theory 3 is incorrect because there are different isotopes and ions of atoms that have small differences between each other. (See my note “isotopes and ions” for more)
JJ Thomson- discovered the electron using the catholic ray tube
- cathode ray tube: electricity passing through a near vacuum
- showed that the radiation was a negatively charged particle smaller than an atom
Millikan: used oil drop experiment to measure the charge and mass of a single electron
Rutherford: used the gold foil experiment to discover the nucleus
- launched particles through a sheet of gold. Most went through, but some occasionally bounced back because it hit the nucleus
Chadwick: found the neutron