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Atomic Theory

12/17/19

Joseph Nam, Douglas Caicedo , Nathanael Ramdyal

Democritus

460-370 B.C.E

Democritus

Born- 460 B.C.E Abdera, Greece

Died- 370 B.C.E ???, Greek

Discovery date - early 400 B.C.E

What did he discovered:

-He developed the concept of the atom,

-The word atom is the greek word for 'indivisible'.

-Democritus believed that everything in the universe was made up of atoms, which were microscopic and indestructible.

Model:

-Grounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles

-He is also known as The Laughing Philosopher as he was often cheerful while at work.

Aristotle

384-322 B.C.E

Aristotle

Born: June 19, 384 BC, Stagira, Greece

Died: March 7, 322 BC, Chalcis, Greece

Discovery date: 332 BCE

What he believed:

-Rejected Democritus Idea of Atomic Theory

-Believed that everything consisted of 4 elements

-Fire, water, earth, and air.

Model:

air which was light, earth which was cool and heavy, water which was wet, fire which was hot

-Aristotle theory was accepted while Democritus theory was disregarded for more than 2000 years.

-There was another element I didn't mention which was Aether which is decided as "a divine substance which made up the stars and planets."

In 338 BCE, He started tutoring son of King Phillip II. The boy who was 13 years old would grow up to be known as Alexander The Great

John Dalton

  • September 6th, 1766---July 27th, 1844

Lived in Eaglesfield and Manchester

  • He proposed that elements are made up of small particles called atoms, atoms in the same element are identical, atoms are unable to subdivide and created or destroyed, and atoms can combine in whole number ratios to form chemical compounds.
  • He based his theory on the assumptions mentioned above (second bullet point)
  • Dalton's model of the atom was a solid indestructible sphere of matter with nothing inside of it.

John Dalton

1803

J.J Thomson

1897

Joseph John Thompson

Born: December 18, 1856, Cheetham Hill, Manchester, United Kingdom

Died: August 30, 1940, Cambridge, United Kingdom

Discovery date: 1897

What he discovered:

-First discovered Electrons

-originally called electrons "corpuscles"

-First evidence of Isotope

-First discovery of subatomic particle

Model:

-The Cathode ray tubes Experiment showed that all atoms contain tiny negatively charged subatomic particles or electrons.

-The Plum Pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged "soup."

Robert Millikan

Robert Millikan

1909

Born: March 22, 1868, Morrison, IL

Died: December 19, 1953, San Marino, CA

What he discovered: 1909

-Determined the mass and charge of the electron

Model:

The Oil Drop Experiment

-They determined the mass and charge of the electron by measuring the effect of an electric field on very small oil droplets. The oil was charged and dropped between two metal electrodes by balancing downward gravitational force with upward drag and electric forces.

- Charge is quantized.

He worked on photoelectric effect (the emission of electrons or other carriers when light hits the material

Ernest Rutherford

Ernest Rutherford

1911

  • August 30th, 1871---October 19th, 1937

Lived in Canada, Nelson, and England

  • Discovered the Nucleus
  • The Gold Foil Experiment was conducted in which alpha particles were shot at a Gold Foil. Some passed right through while others were deflected, revealing that the atom was made up of mostly empty space, and the atom contained a small, dense piece at the center called the nucleus.
  • Rutherford also invented a radio receiver, discovered that atoms were not indestructible, discovered alpha and beta radioactivity, and discovered the proton.

Neil Bohr

1913

Neil Bohr

Born: October 7, 1885, Copenhagen, Denmark

Died: November 18, 1962, Carlsberg, Copenhagen, Denmark

Discovery date: 1913

What he discovered:

-Discovered sets of number of electron orbit

-Electron orbit around the atomic nucleus

-Electrons can only move from one to another at one time either being absorbed or emitted called quanta

-discovered The number of electrons in the outer orbit determines the properties of an element.

-foundational contributions to understanding atomic structure and quantum theory

Model:

The Bohr model shows the atom example as a small, positively charged nucleus surrounded by orbiting electrons.

He was awarded multiple noble prize from discoveries ranging from how cells adapt to changes in levels of oxygen to our ability to fight global poverty.

Erwin Schrodinger

Erwin Schrodinger

1926

  • August 12th, 1887---January 4th, 1961. lived in Vienna, Austria
  • He used mathematical equations to describe the likelihood of finding an electron in a certain position.It is known as the Quantum Mechanical model of the atom.
  • He developed the equation by exploiting the wave-like behaviors from atomic particles
  • He was the first person to explain the movement of electrons with visuals, and the second to explain the idea.
  • He was awarded the 1933 Nobel Prize in Physics for coming up with a groundbreaking wave equation for electron movements.

James Chadwick

James Chadwick

1932

  • October 20th, 1891---July 24th, 1974.
  • Lived in England; various cities
  • He discovered the existence of the neutron.
  • He found this by looking at alpha waves (positive charge), that bounced off the nucleus, saying that there was no charge in the nucleus, hence the name "Neu(tral)-tron"
  • The neutron contributed to the atomic weight with the same effect as a proton.
  • He was awarded a Nobel prize in Physics in 1935 for his discovery of the neutron
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