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Chemistry Project: The Structure of The Atom

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Anita Karimu

on 3 October 2012

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Transcript of Chemistry Project: The Structure of The Atom

Anita Karimu The Structure of The Atom This presentation takes us on a walk through the life and development of the Structure of the Atom. The Structure of the atom has gone through many stages of development before reaching the current model we know of today. Around 400 BC there was a Greek Philosopher named Democritus. He had the concept that if you take any material and continuously divide it in half you would eventually reach a tiny indivisible particle of that material. He used the word 'Atomos' to describe this particle. Democritus Democritus was not a scientist and did not have evidence to prove his claim so it was not widely believed. In 1803 a scientist named John Dalton introduced a theory that has the following principles:
1. Matter is composed of tiny particles called ATOMS that are indivisible.
2. Atoms cannot be made or destroyed
3. Atoms of one element are different from that of a different element
4. Compounds are formed from atoms of the constituent elements in whole number ratios. Dalton Dalton's atom was a featureless sphere. it was an indivisible ball. In 1904 Thompson,while using a cathode ray scope, stated that all matter is made up of particles that are less massive than the atoms the form a part of. This statement led to the discovery of what we know of as electrons which he called corpuscles.

He also studied rays know a canal rays. these were positively charged rays created by some types of gas discharge tubes.

Thompson used the knowledge to form his theory that atoms had negative particles within them that were 'suspended' or held in a gel of positive charge. Joseph J. Thompson In 1859 a scientist named J. Plucker built a gas discharge tube which is now called a cathode ray.

20 years later Sir William Crookes discovered that the cathode rays produced by this discharge tube were negatively charged, travel in straight lines, cause glass to fluoresce and have mass. Plum Pudding Model Thompson's model was comprised of a large sphere of uniform positive charge embedded with smaller negatively charged particles (corpuscles) In 1911 another scientist named Ernest Rutherford wanted to test Thompson's theory. He conducted the Gold Foil experiment. Ernest Rutherford In this experiment Rutherford shot a beam of charged alpha particles through a foil of gold which was only about 0.00004 centimeter thick. He placed a zinc sulphide coated screen around the exit area to record the path of the particles.
If Thompson's model was accurate then the alpha particles should pass through with little deflection. Hence they would only strike the screen directly behind the foil. Gold Foil Experiment When the experiment was conducted it was noted that though most of the particles came straight through the foil some were deflected at large angles and some even bounced back to the source. Results Of the Gold Foil Experiment This led Rutherford to conclude the Thompson's model of the atom was inaccurate. Rutherford developed his own model in which the atom has a central positive nucleus (where all its positive charge and mass is held) surrounded by orbiting electrons and empty space. Bohr was a Danish Physicist. In 1913 after studying Rutherford's model and the behavior of electrons he stated his theory that electrons in an atom orbit the nucleus in successively larger orbits.He also stated that as electrons move to a lower orbital they emit a photon int he form of light.

His atomic model had the nucleus in the center with electrons orbiting it at different levels. Each outer level holding more electrons than the one below it. Niels Bohr Bohr's Model seemed to some scientist to contradict common sense. The model had technical issues (the concept only worked for hydrogen atoms) that had to worked on before it would be completely accepted as true. In the years post 1930 Scientists applied the concept of quantum theory to the atomic structure proposed by Bohr. This model is based on mathematics.
Four quantum numbers were developed and used to describe elections and their positions in orbitals.
These are:
Principal quantum number
Angular momentum quantum number
Magnetic quantum number
Spin quantum number Quantum Mechanical Model Summary of the Development of The Atomic Structure The models used today are the Bohr Model and the Quantum Mechanical Model. Using these numbers electrons can be placed into exact orbitals which have specific shapes and capacities. There is an 's' orbital, a 'p' orbital, a 'd' orbital and an 'f' orbital. Which can hold 2, 8,10 and 14 electrons each respectively. University of Georgia Website ,Lecture notes for GEOL 3010, Significant event in Timeline;

Dummies.com, Atomic Structure: The quantum Mechanical Model, Significant Event in Timeline;

Atomictimeline.net, All, Basic Background Information;


Modern Chemistry Textbook, chapter 3 and 4, Significant events on Timeline;

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