History of the Atom

Scientists and Their Contribution to the Model of an Atom

Democritus proposes

the 1st atomic theory

460 – 370 BC

History of the Atom - TimelineAntoine Lavoisier

makes a substantial number of contributions

to the field of Chemistry

1766 – 1844

John Dalton proposes his

atomic theory in 18031743 – 1794

0

1856 – 1940

J.J. Thomson discovers the electron and proposes the Plum Pudding Model in 1897

1871 – 1937

Ernest Rutherford performs the Gold Foil

Experiment in 1909

1885 – 1962

Niels Bohr proposes the Bohr Model in

1913

1887 – 1961

Erwin Schrodinger describes

the electron cloud in 1926

1891 – 1974

James Chadwick

discovered the neutron in in 1932

170

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180

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190

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Democritus(460 BC – 370 BC)

• Proposed an Atomic Theory(along with his mentor Leucippus) which states that all atoms are small, hard, indivisible and indestructible particles made of a single material formed into different shapes and sizes.

• Aristotle did not support his atomic theory Image taken from: https://reich-

chemistry.wikispaces.com/T.+Glenn+Time+Line+Project

Alchemists(500 BC – 1720)

Now, they wanted to live forever, so they started out with trying to make a potion that could make them live forever. They didn’t succeed, but they did make many experiments, and the scientific method. They also kept careful records.

Antoine Lavoisier(1743 – 1794)

Known as the “Father of Modern Chemistry”

Was the first person to generate a list of thirty-three elements in his textbook

Devised the metric system Was married to a 13-year old Marie-Anne

Pierette Paulze; she assisted him with much of his work

Was a tax-collector that was consequently guillotined during the French Revolution

Discovered/proposed that combustion occurs when oxygen combines with other elements

Discovered/proposed the Law of Conservation of Mass (or Matter) which states, in a chemical reaction, matter is neither created nor destroyed

Image taken from: www.ldeo.columbia.edu/.../v1001/geo

time2.html

John Dalton (1766 – 1844)

In 1803, proposed an Atomic Theorywhich states:o All substances are made of atoms;

atoms are small particles that cannot be created, divided, or destroyed.

o Atoms of the same element are exactly alike, and atoms of different elements are different

o Atoms join with other atoms to make new substances

Calculated the atomic weights of many various elements

Was a teacher at a very young age Was color blind Image taken from:

chemistry.about.com/.../John-Dalton.htm

1898

Marie & Pierre Curie

They both picked up on Becquerel’s work on uranium, which lead them to find the elements radium and polonium. Though Marie went further with the radioactivity of elements, she didn’t get very far. All she said was, “they were somehow disintegrating over time and emitting radiation that exposed the plate.” ~ Marie Curie

http://www.neoam.cc.ok.us/~rjones/Pages/online1014/chemistry/chapter_8/pages/history_of_atom.html#becquerel-curie%20anchor

Pierre went on to say that atoms might be composed of even smaller things.

• He described radioactivity. He found this out from unknown x-rays waves, which were produced by uranium.

• Penetrating radiation was also discovered by Becquerel.

• Discovered that uranium was able to expose a photographic plate on black paper, and didn’t depend on the chemical state.

Henri Becquerel(1851-1908)

Image taken from: chemistry.about.com/.../HenriBecqu

erel

1900

Max Planck

He was the person who came up with the original quantum theory. To come up with this, all he did was research from pervious scientists and a little bit on his own, and then wrote a book on the quantum theory (the theory: the behavior or matter and energy in an atom). He also was looking at color changes from energy. He also made a math equation to help with this theory.

1905

Albert Einstein

First, he found that nature and matter intertwine somehow, the theory of measurement came about from this. Second, he publish 5 papers on electrons. These contributed to the quantum mechanics. He said, “light consists of quanta, bundles of energy which behave somewhat like particles.” ~Albert Einstein

http://www.crystalinks.com/einstein.html

1908

Robert Millikan

He was by far the most famous American scientist. He wanted to find the electrical charge of electrons. He measured water droplets, and that wasn’t successful, so he measured oil droplets, where all this proved electrons were negatively charged. He also was a professor for many years, and wrote many textbooks on chemistry.

J.J. Thomson (1856 – 1940)

Proved that an atom can be divided into smaller parts

While experimenting with cathode-ray tubes, discovered corpuscles, which were later called electrons

Stated that the atom is neutral In 1897, proposed the Plum Pudding

Model which states that atoms mostly consist of positively charged material with negatively charged particles (electrons) located throughout the positive material

Won a Nobel Prize

Image taken from: www.wired.com/.../news/2008/04/d

ayintech_0430

Ernest Rutherford (1871 – 1937)

In 1909, performed the Gold Foil Experiment and suggested the following characteristics of the atom:o It consists of a small core, or nucleus,

that contains most of the mass of the atom

o This nucleus is made up of particles called protons, which have a positive charge

o The protons are surrounded by negatively charged electrons, but most of the atom is actually empty space

Did extensive work on radioactivity (alpha & beta particles, gamma rays/waves) and was referred to as the “Father of Nuclear Physics”

Won a Nobel Prize Was a student of J.J. Thomson Was on the New Zealand $100 bill

Image taken from: http://www.scientific-

web.com/en/Physics/Biographies/ErnestRutherford.html

1938

Otto Hahn & Lise Meitner

While working in a lab, Otto Hahn discovered radiothorium, and then later

discovered 5 more elements. He also discovered radioactive recoil. Lise

Meitner was he partner when they discovered the isotope of protactinium.

His biggest discovery was barium as a fission element. He combined results

with Otto Frisch and they came up with nuclear fission. He was testing

uranium and how it busted into lighter elements. Lise always studied

radioactivity. She, herself, discovered the auger effect.

Niels Bohr (1885 – 1962)

In 1913, proposed the Bohr Model, which suggests that electrons travel around the nucleus of an atom in orbits or definite paths. Additionally, the electrons can jump from a path in one level to a path in another level (depending on their energy)

Won a Nobel Prize

Worked with Ernest Rutherford

Image taken from: commons.wikimedia.org/wiki/File:Ni

els_Bohr.jpg

Erwin Schrodinger (1887-1961)

• In 1926, he further explained the nature of electrons in an atom by stating that the exact location of an electron cannot be stated; therefore, it is more accurate to view the electrons in regions called electron clouds; electron clouds are places where the electrons are likely to be found

• Did extensive work on the Wave formula Schrodinger equation

• Won a Nobel Prize

Image taken from: nobelprize.org/.../1933/schrodinger

-bio.html

James Chadwick (1891 – 1974)

Realized that the atomic mass of most elements was double the number of protons discovery of the neutron in 1932

Worked on the Manhattan Project

Worked with Ernest Rutherford

Won a Nobel Prize Image taken from:

www.wired.com/.../news/2009/02/dayintech_0227

1951

Glenn T. Seaborg

Glenn was best known for identifying and discovering elements that were heavier then uranium. He also isolated 10 elements. He also proposed the “actinides” in the element table. He discovered these elements just by separating different elements, and combining different elements.

1964

Murray Gell-Mann & George Zweig

Murray Gell- Mann was an American physicist who received a Nobel Prize for his theory

on elementary particles. He also found that all the elements of an atom are held together

by quarks. To find this, he blasted high speed electrons into a hydrogen atom.

George Zweig proposed the existence of quarks. He thought of them as aces, because

he guessed there were four quarks in every atom.

Now, in the same year, both these guys proposed the idea of quarks. They tested

electrical charges, and that how the numbers for quarks came about.

Werner Heisenberg

1925Heisenberg Uncertainty

Principle – It is impossible to determine the position and velocity of an

electron simultaneously.

Heisenberg uncertainty

principle

• In order to observe an

electron, one would need

to hit it with photons having

a very short wavelength.

• Short wavelength photons

would have a high

frequency and a great deal

of energy.

Progression of the Atomic Model

The structure of an atom, according to: Democritus & John Dalton

J.J. ThomsonErnest RutherfordNeils BohrErwin SchrodingerJames Chadwick

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