By Bekah Clark and Laura Trafidlo

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1803- John Dalton

In 1803, John Dalton proposed an “atomic theory” with round, solid atoms based upon measurable properties of mass.

1869- Dmitri Mendeleev

In 1869, Dmitri Mendeleev arranged the elements into seven groups with similar properties. He discovered that the properties of elements “were periodic functions of their atomic weights”. This became known as the periodic law.

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1874- G. J. Stoney

In 1874, G. J. Stoney proposed that electricity was made of subtle negative particles he called “electrons”.

1897- J. J. Thompson

In 1897, J. J. Thompson used a CRT (cathode ray tube) to experimentally determine the charge to mass ratio of an electron. Later in that same year, he studied “canal rays” and found they were associated with the proton H+.

1898- Marie Curie

In 1898, Marie Curie (with the assistance of her husband Pierre) discovered the radioactive elements polonium and radium. She also studied uranium and thorium.

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1900- Soddy

In 1900, Soddy observed the impulsive collapse of radioactive elements into alternatives he called “isotopes”.

1911- Ernest Rutherford

In 1911, Ernest Rutherford established that the nucleus was very dense, very small, and positively charged.

1914- H. G. J. Moseley

In 1914, H. G. J. Moseley said that the atomic number of each element is equal to the number of protons in the nucleus. This information was used to reorganize the periodic table by atomic number, not atomic mass.

1932- James Chadwick

In 1932, James Chadwick discovered a neutral atomic particle with a mass close to a proton. This was known as the neutron.

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1942- Enrico Fermi

In 1942, Enrico Fermi conducted the first controlled chain reaction releasing energy from the atom’s nucleus.

1995- Joseph Polchinski

In 1995, Joseph Polchinski ignited the D-brane revolution in string theory with his paper describing extended objects in string theory formed by dual open strings with Dirichlet boundary conditions.

An open string

A closed string

Glossary of Terms

NAME DEFINITION NAME DEFINITION

CRT a vacuum tube in which a stream of electrons is produced and directed onto a fluorescent screen

Canal rays A positive ray

isotope form of an element with the same atomic number

Bibliography Super String Theory

(http://www.superstringtheory.com/basics/basic4.html)

Atomic Structure Timeline (http://watertown.k12.wi.us/HS/Staff/Buescher/atomtime.asp)

String Theory Timeline (http://www.superstringtheory.com/history/history3.html)

“Matter: Building Block of the Universe” (3rd ed.) by Anthea Maton et al. ©1997, 1994 , 1993 Prentice Hall- New Jersey

Copyright 2004 by Bekah Clark and Laura Trafidlo for Mr. Mullen’s 8th grade science class

F-Block Science

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