Atom History

Question 1

John Dalton

Answer 1

1803
Dalton’s atomic theory:
1.
Dalton’s Atomic Theory
1) All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties
3) Atoms of a given element are different than those of any other element.
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) Atoms are not created nor destroyed in a chemical reaction.

Question 2

Democritus

Answer 2

300 B.C.

theorized that elements were fire, water, earth, and air

Question 3

JJ Thomson

Answer 3

1897

discovered the electron using the cathode ray tube to form the plum pudding model

Question 4

Millikan

Answer 4

1909
determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron in the oil drop experiment

Question 5

Ernest Rutherford

Answer 5

1911
Using alpha particles (heavy positively charged particles)as atomic bullets, probed the atoms in a piece of thin gold foil . He established that the nucleus was: very dense, very small and positively charged.

Question 6

Henry Moseley

Answer 6

1914
determined the charges on the nuclei of most atoms and discovered the atomic number (equal to the number of protons in the nucleus)

Question 7

Niels Bohr

Answer 7

1922

discovered that atoms contain electrons that formed successive orbits

Question 8

Erwin Schrodinger

Answer 8

1930

• introduced “wave mechanics” as a mathematical model of the atom in a quantum mechanical model
• his equation limits an electron’s energy to certain values and calculates the likelihood of finding an electron in a particular location

Question 9

James Chadwick

Answer 9

1932

discovered the neutron using alpha particles discovered a neutral atomic particle with a mass close to a proton.