Atomic Numbers

Henry Moseley (1887 - 1915)

“Moseley, as it were, called the roll of the elements, so that for the first time we could say definitely the number of possible elements between the beginning and the end, and the number that still remained to be found.”

Ions in Water Solution

Mass Spectra

Mass Spectroscope

Francis William Aston (1877 - 1946)

Modern Mass Spectroscope

Hydrogen Spectrum

Atomic Weights of Some IsotopesElement Isotope Atomic Weight

Hydrogen 1H 1.0078252H 2.01410

Helium 4He 4.0026

Carbon 12C 12 (exactly)13C 13.00335

Oxygen 16O 15.9949117O 16.9991

Neon 20Ne 19.9924421Ne 20.9939522Ne 21.99138

Chlorine 35Cl 34.9688537Cl 36.9659

Uranium 235U 235.0439238U 238.0508

Mass Number (A) Isotopic Mass (amu) % Abundance

196 195.165 0.14

198 197.967 10.04

199 198.967 16.83

200 199.968 23.12

201 200.970 13.23

202 201.970 29.79

204 203.973 6.85

Mercury Spectrum

Atomic Number

Atomic Weight

Atomic Structure

Worked with:Hans GeigerErnest Marsden

Ernest Rutherford (1871 - 1937)

Gold Foil Experiment

Then I remember two or three days later Geiger coming to me in great excitement and saying, “We have been able to get some ofthe alpha particles coming backwards…” It was quite the mostincredible event that has ever happened to me in my life. It wasalmost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it cam back and hit you.

Radioactive Elements

Pitchblende

Pierre and Marie Curie

Large Nuclei