In today's class, Mr. Doktor discussed atomic theory. There were seven significant people who's ideas contributed to the development of atomic theory: the Greeks, Lavoisier (late 1700s), Proust(1799), Dalton (early 1800s), J.J. Thomson (1850s), Rutherford (1905), and Bohr (1920s).Some important points..
The Greeks:
- in 3000 BC, Democritus said that atoms were indivisible particles
- first mention of atoms
- only a conceptual model
- was the accepted view for over 2000 years
Lavoisier:
- Law of conservation of mass
- Law of definite proportions
*wasn't a true atomic theory because it did not discuss what atoms were or how they were arranged
Proust:
- if a compound is broken down into its constituents, the products exist in the same ratio as in the compounded form
- experimentally proved Lavoisier's Laws
Dalton:- atoms are solid, indestructible spheres (like billiard balls)
- provides for different elements
J. J. Thompson:
- used the raisin bun model
-solid, positive spheres with negative particles embedded in them
- first atomic theory to have positive (protons) and negative (electron) charges
- introduced the idea of nucleus
Rutherford:
- showed that atoms have a positive, dense center with electrons outside it
- resulted in a planetary model
- explains why electrons spin around nucleus
- suggests atoms are mostly empty space
- should be unstable (electrons and protons should attract and destroy the atom)
Bohr:- electrons must only exist in specific orbitals around nucleus
- explains how valence electrons are involved in bonding
- explains the difference between ionic and covalent bonding
- resolves the problem of atomic instability
- includes the neutron (discovered in 1932)
- explains atomic emission spectra
Review Questions:
1. Who first mentioned atoms? Democritus
2. Who introduced the idea of nucleus? J. J. Thomson
3. Who stated that atoms were indestructible? Dalton
4. Who explained bonding and 'levels' around the nucleus? Bohr
5. Who explained why electrons spin around the nucleus? Rutherford
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