The Evolution of the Atomic Model

The Evolution of the Atomic Model

Calvin Engstrom, Block D

Democritus

J. J. Thomson

Niels Bohr

This man of Abdera, Greece founded the study of atoms.

weren't

He found that atoms the smallest things in the universe after all.

His research added greatly to our understanding of the electron.

All of this leading up to our current understanding of the atom, providing a foundation for even more exploration of the atom and its potential...

A Few Interesting Facts...

Important

Information

• One of his famous quotes is: "To the electron: may it never be of any use!”

MAIN IDEA

Democritus believed that if you cut an object in half, and then cut again and again, there would come a point where it couldn't be split. He proposed that at the point where it could not be divided again there was a single particle: an atom.

Democritus dubbed the particle an atom because it stemmed from the word "atomos" which means "indivisible." (The prefix "a" means "not" and the root "tomos" means "cut.")

ATOMOS

• In September 1943, Bohr and brother Harald were living in Nazi-occupied Denmark. Since their mother was born Jewish, the brothers were forced to flee to Sweden for safety.

• The Democritus University of Thrace in Xanthi, Greece was named after this philosopher.

• Thomson was awarded the 1906 Nobel Prize in Physics "in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases."

Discovery

Model

British scientist Joseph John (J. J.) Thomson discovered that there are smaller particles within the atom itself. The particles that he investigated were negatively charged electrons, although they weren't dubbed this until well after his research. With this find, John Dalton's theory that atoms were indivisible was disproved.

Thomson's model of the atom was called the "plum pudding" model.

Important

Information

Experiment

Thomson performed his experiments using a cathode-ray tube. Particles were fired between two plates, one positively and one negatively charged, and when those plates were charged, the beam was pulled toward the positive plate. Thus, Thomson came to the conclusion that these particles were both negatively charged and present within every type of atom.

Discovery

Niels Bohr suggested that electrons don't haphazardly whirl around the nucleus, but instead they travel along certain paths or energy levels.

Model

Bohr's model suggested several energy levels that the electrons could travel on, each one holding more electrons than the last.

• Bohr was an advocate for the use of atomic research in a productive and constructive way. He even organized the Atoms for Peace conference of 1955 and received the Atoms for Peace award in 1957.

• He appeared on a Greek 100 drachma note which is now out of circulation.

Important

Information

440 BCE

England

Greece

1897

Present

Denmark

1913

Day

England

1803

England

1909

Austria/Germany

1926

Ernest Rutherford

Schrödinger and

John Dalton

Important Information

Discovery

Rutherford proposed that at the center of an atom was a miniscule, positively charged nucleus. He also concluded that atoms were mostly empty space with very tiny and very dense components, completely changing what was previously thought to be true.

Experiment

His work completely redefined the atomic model.

The experiment which Rutherford drew his conclusions from involved aiming a beam of positively charged particles at a thin sheet of gold foil. Nearly surrounding this foil was material with a special coating that would glow where particles hit it. He found that some passed straight through, some were slightly deflected, and some bounced almost straight back.

These work of these men contributed significantly to the modern atomic model.

Model

Rutherford's model suggested that there was actually a relatively vast amount of space between the parts of an atom. (Note: This diagram is not to his calculated scale, and neutrons were not discovered until 1932.)

A Few Interesting Facts...

He was one of the first pioneers of modern atomic theory.

A Few Interesting Facts...

• Both of these men received Nobel prizes for their work.
• Heisenberg remained in Germany throughout the entirety of World War II.
• Schrödinger met Albert Einstein while working at the University of Berlin.

• Dalton was also very interested in color blindness, for both he and his brother were afflicted with the condition.

• He was a member of the Commonwealth Order of Merit, an elite group of high-achieving individuals nominated by the monarch of the Commonwealth realms. Some former members and honorary members include Nelson Mandela, Mother Teresa, and Sir Winston Churchill. With admission, he was also granted the title First Baron Rutherford of Nelson.

Important

Information

Werner Heisenberg left, Erwin Schrödinger right

Atomic Theory

Dalton's theory consisted of three

main points:

• All substances are made of atoms, or small particles which cannot be created, divided, or destroyed.
• Atoms of the same element are identical, and atoms of different elements are likewise different.
• Atoms are able to join with other atoms to form new substances.

He believed the atom to be round and smooth.

• At the age of 12, he was already teaching at a Quaker school in Cumberland, England.

Important

Information

Heisenberg

Discovery

• Rutherford was buried in Westminster Abbey among other great British scientists (even Sir Isaac Newton!).

They found that Bohr was wrong, for electrons don't travel in definite paths. Instead, Schrödinger and Heisenberg said that the precise path of an electron is unpredictable. They suggested that there are places where they may be found called electron clouds.

Model