Elements

& Atoms

Demokritos c. 460-370 BC

“The material cause of all things that exist is the coming together of atoms and void. Atoms are too small to be perceived by the senses. They are eternal and have many different shapes, and they can cluster together … By aggregation they provide bulky objects that we can perceive with our sight and other senses… There is no void in atoms, so they cannot be divided.”

“Atomos” = “indivisible”

• too small to see

• indivisible

• solid

• make up everything

Aristotle384-322 BC

• 4 “elementary” substances: earth, air, fire, and water

• Matter is continuous (no atoms)

“Material objects are of two kinds: atoms and compounds of atoms. The atoms themselves cannot be swamped by any force, for they are preserved by their absolute solidity.”

Re Rerum Natura 50 BC

99-55 BC

few Greek

or Romanatomists

Robert Boyle

1627 --1691

Boyle on Elements c.

1661

• “true” elementary substances as proposed by Greeks and alchemists can’t be purified in the lab

• new operational definition of elements as “substances that cannot be simplified by physical or chemical means”

John Dalton1766--1844

Atoms are the smallest parts of elements.

Atoms are indivisable.

Atoms of each element have unique mass.

Atoms of the same element are all identical. C. 1803

JJ Thomson1856-1940

studies engineering at Manchester University, but gets his BA in Mathematics at Cambridge, where he stays for the rest of his life

holds Cavendish Chair in Experimental Physics at Cambridge from 1884 - 1918

wins Nobel Prize in Physics 1906

Experiments with Crooks tubes and other apparatus in 1890s led to Thomson’s publication in 1897 of hypothesis that atoms are made of negatively charged “corpuscles” moving in a sea of positive charge.

1897

Ernest Rutherford1871-1937

doctoral student of Thomson 1895-1989

Physics Chair at McGill from 1898-1907 before returning to England and teaching at Manchester University

wins Nobel Prize in Chemistry 1908 (for radioactivity work)

takes over Cavendish Chair of Physics from Thomson in 1919

Geiger-Marsden Experiment 1909

Interpreted by Rutherford: The Nucleus!

Hans Geiger

• nucleus is very small

• nucleus contains all positive charge (p+)• electrons are outside nucleus

James Chadwick1891-1974 1911 BS in Physics at

Manchester University; gets MS under Rutherford in 1913

1913 travels to Germany to work with Hans Geiger; interned in Germany for WWI

returns to England after WWI, works under Rutherford at Cambridge

1932 experimental evidence of neutrons, which Rutherford hypothesized would need to exist to counteract repulsion of protons within the nucleus

1935 Nobel Prize in Physics 1943-’46 Manhattan Project USA

• much easier to measure charged particles!

• neutrons have no charge

• neutrons account for “missing mass” in atoms

Niels Bohr1885-1963

1911 gets PhD in Physics in native Copenhagen University and comes to UK

1911 works with Thomson in Cambridge

1912 works with Rutherford in Manchester

1913 returns to Copenhagen University

1922 Nobel Prize in Physics1920 becomes first head of

Institute of Theoretical Physics in Copenhagen, remains head until 1962

Bohr Model(also called “Bohr-Rutherford” model)

• Developed from work with Rutherford in 1912 and published in 1913

• “planetary” model accounts for atomic spectra data

• FAILS for spectra after hydrogen

Werner Heisenberg 1901-1976• 1923 PhD in Munich

• 1924-’25 works with Bohr in Copenhagen

• establishes “quantum mechanics” when only 23 years old in 1925 - includes Uncertainty Principle

• 1932 Nobel Prize in Physics• 1941 director of Kaiser

Wilhelm Institute in Berlin - captured by US troops at end of WWII & sent to England; returns to Germany after the war

• can’t know position and motion of an electron simultaneously• electrons can’t be

described with the particle math of Newton

Prince Louis-Victor deBroglie

1892-1987• educated and worked in

France - BA in 1913 & graduate work after serving for France in WWI

• his 1924 doctoral thesis introduced “wave mechanics” - the idea that the electron could be treated as a wave

• 1929 Nobel Prize in Physics

Erwin Schrødinger 1887-1961• educated in Vienna; serves

in Austrian Army in WWI• 1926 publishes “wave

equation” model of electrons

• Goes to Germany in 1927 but leaves in 1933 with rise of Nazis; ends up in Austria in 1937; recants opposition to Nazis but is harassed and escapes in 1938

• 1933 Nobel Prize in Physics with Dirac

• 1940 establishes Institute for Advanced Studies in Dublin

• describes electron location with probabilities

• Bohr “orbits” Schrødinger “orbitals”

• new (math) model very difficult to visualize

computer-generated images of “electron

cloud” shapes generated by Schrødinger’s

wave equation

meta-synthesis(chem education co.)