History Of The Atomic Model

460BC

1803-1805

Democritus' Atomic Theory was left untouched until 1803, when english chemist, John Dalton came to challenge the Aristotelian theory. Born in the country of Cumberland, England, he was the creator of the atomic theory of matter, which was a compostiion of Democritus' and his own findings. Disapproving Aristole with pure scientific evidence, John Dalton showed that common elements always broke down into the same elements with the same shape and proportions. His theory was now accepted into the scientific community.

His theory had 5 major predictions:

1. All matter is made of atoms

2. Atoms cannot be created or destroyed

3. All atoms of the same element are identical

4. Chemical reactions occur when atoms are rearranged

5. Compounds are formed by the combination of 2 or more different kinds of atoms.

1904

Joseph John Thompson was born in Manchester, England. From a young age J.J Thompson demonstrated extraordinary talent and showed great interest in science.

In his adult years, he started to work on the already accepted atomic theory by John Dalton. Up until his time, every atomic diagram looked like a big solid ball.He discovered the electron, a tiny sub atomic partiicle that other scientists attempted to find but failed at doing so. He found electrons through his explorations with cathode rays. This led him to create the "plum pudding" atomic model. In this model, he thought that atomics were mostly positive, and negative particles moved around the outside. This atomic model influenced many other scientists to make better models.

Philipp Lenard was a German Physicist, active nationalist and nobel prize of physics, he originated from Austria.

Philipp Lenard's major contributions to the making of the atomic theory was based around his work on cathode rays. Before his time, cathode rays were poor quality, primitive, it was difficult for scientists to study the arrangement. Lenard was able to fix this problem by introducing "Lenard windows" which are metallic windows that were used in experiments that were very convientient for scientists to study. He was able to detect the rays and measure their intensity using his windows (paper sheets coated with phosphorescent materials).

Niels Henrik David Bohr was a Dainish Phyicist who was a student of Rutherford. He was born in Copenhagen, Denmark. He was the child of Christan Bohr, a professor of physiology at the University of Copenhangen and Ellen Bohr, who was a decentant from a wealthy jewish family.

Niels Bohr made a new atomic model based off Rutherford's model. Niels showed that electrons travel in seperate orbits and that there are energy levels in an atom. Only a certain amount of electrons could fit into one energy level of an atom.

James Chadwick was an English Physicist who perfected atomic model. He was born in Cheshire, United Kingdom. He was an exempliary student and he was given a scholarship at Manchester Grammar School, but his parents had to turn it down as they couldnt afford to pay for the small fees that were left over. So he went to the central grammer school for boys in Manchester, he was an extrodinary student and at the age of 16, he sat 2 exams for university scholarships, and won both of them.

James was well known for his discovery of the neutron and for the completion of the atomic model. He worked with Ernest Rutherford at the University Of Cambridge. Rutherford model concluded that the nucleus was made of just protons, and people believed that was correct because it made sense if the negative particles cancelled out the positive particles. Later on, both Rutherford and Chadwick questioned why there was a difference between the atomic mass and the number of protons. He then saw how scientists Frederic and Irene Joliot-Curie were used methods to track particle radiation. He used a similar method but this time, he was searching for the existense of a neutron. His experiments were successful and he was given a nobel prize in 1935 for his discovery.

Referencing

Bibliography

History of the Atomic Model timeline | Timetoast timelines. 2015. History of the Atomic Model timeline | Timetoast timelines. [ONLINE] Available at: https://www.timetoast.com/timelines/history-of-the-atomic-model--36. [Accessed 11 October 2015].

Niels Bohr - Wikipedia, the free encyclopedia. 2015. Niels Bohr - Wikipedia, the free encyclopedia. [ONLINE] Available at: https://en.wikipedia.org/wiki/Niels_Bohr. [Accessed 11 October 2015].

PhysicsLAB: Famous Experiments: The Discovery of the Neutron . 2015. PhysicsLAB: Famous Experiments: The Discovery of the Neutron . [ONLINE] Available at: http://dev.physicslab.org/Document.aspx?doctype=3&filename=AtomicNuclear_ChadwickNeutron.xml. [Accessed 11 October 2015].

Neutron Discovery. 2015. Neutron Discovery. [ONLINE] Available at: http://chemistry.bd.psu.edu/jircitano/neutron.html. [Accessed 11 October 2015].

History Of The Atomic Model

Ernest Rutherford

J.J Thompson

James Chadwick

Democritus

460BC-370BC

30 August 1871-19 October 1937

18 Dec. 1856-30 Aug. 1940

20 October 1891-24 July 1974

Democritus, a Greek influential philosopher, was the first to believe that everything was made up of "atoms", he is primarily remembered nowadays as the first to formulate an atomic theory. His theory was that everything was made of tiny particles, surrounded by empty space, he also guessed that these particles change size and shape depending on the matter they create. He called these particles "atomos".

Ernest Rutherford was a British physicist well known for his work on nuclear physics. Although he was British, was born in New Zealand as his Father emigrated from Scotland. He was under the leadership of J.J Thompson in his time spent at Cambridge University.

Ernest Rutherford discovered that J.J Thompson's theory was a little incorrect, he found that instead postivite matter being the whole atom, it is only found in the middle and surrounded by empty space. He also said the electrons surround the positive nucleus. His new atomic model was later perfected by his own students.

1904, J.J Thompson's Atomic model

1909, Ernest Ruthford's Atomic Theory

Democritus's model of the atom

J.J Thompson's Cathode Ray Experiment

Modern Day Atomic Model

In the modern day atomic model, electrons are in a constant motion around the nucleus. Inside the nucleus, protons and neutrons figet around. Although pictures show that electrons, protons and neutrons are the same size. In reality, protons and neutrons are alot smaller than electrons.

Protons have a positive charge.

Electrons have a negative charge.

And Neutrons have no charge.

There is a little difference between the Bohr' atomic model and the modern day one. The difference is that the modern day atomic model has electrons orbiting the nucleus in a wave-like form, whilst in Bohr's thought that electrons orbit the nucleus.

The modern day atomic model is based off the quantum theory, which explains the behaviour of matter and energy on an atomic and subatomic level.

2000

2005

2010

Niels Bohr

Philipp Lenard

John Dalton

September 6, 1766-July 27, 1844

7 October 1885-18 November 1962

7 June 1862-20 May 1947

1905, Philipp Lenard's Atomic Model

Niels Bohr, 1913

John Dalton's atomic model