Atomic Theory Mr. Tollefson Chemistry Class. Introduction Students will be introduced to the atom and the development of the atomic theory from ancient.

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Presentation transcript:

Atomic Theory Mr. Tollefson Chemistry Class

Introduction Students will be introduced to the atom and the development of the atomic theory from ancient times to the present day.

The Atom Democritus an Ancient Greek philosopher first purposed the word ‘Atom’ around 375 BC. The atom was defined as a small round indivisible particle. The idea of the Atom had to wait for 2200 years to be proven.

Dalton and Atomic Theory John Dalton’s (d1844) Atomic Theory consists of 4 parts. –All elements are composed of indivisible particles called atoms. –Atoms of the same element are identical. Atoms of element are different from others. –Atoms can mix together in whole number ratios –Chemical reactions occur when atoms combine, separate or rearrange

Electron’s: Discovery 1897 The English physicist Sir JJ Thompson discovered the electron in He experimented with sealed tubes with gases in them. He passed high voltage electric current through the tubes. The glowing beam created is called a cathode ray.

Cathode Rays Thompson found that the rays were attracted to metal plates that carry positive charges. Thomson proposed that a cathode ray is composed of tiny negatively charged particles about 1/2000 the mass of the hydrogen atom. He called them electrons.

Plum Pudding Thomson also worked with modified cathode ray tubes that gave rays traveling in the opposite direction. These particle were found to have the same amount of charge as electrons, just the opposite sign. These were later called protons.

PLUM PUDDING From what Thomson learned about protons and electrons he proposed his ‘Plum Pudding’ model of the atom. Protons and electrons are mixed together in a big blob with no particular order.

Nucleus Ernst Rutherford made a major advance in atomic theory with a simple experiment with complex results(1912). Sometimes called the ‘gold foil experiment’ it is the foundation of the modern atom.

Radioactive Source Gold Foil Phosphorescent Screen Alpha Radiation

GOLD FOIL EXPERIMENT Using a radioactive source Rutherford fired alpha particles at a very thin piece of gold foil. He expected the alpha particle to easily pass through the foil and strike the screen on the opposite side. He found that some of the particles were deflected at small angles and some were reflected back.

Nucleus The results of Rutherfords experiment was his proposal of the nuclear atom. He proposed that in the center of an atom was a very small and dense ‘nucleus’ and that the nucleus was composed of protons.

BOAR? Neils Bohr worked with Lord Rutherford for a short while and came up with his own hypothesis for the structure of an atom. It is called the planetary model of the atom.

Planetary Atom The only difference between the planetary atom and the Rutherford atom is the placement of the electrons in orbitals. Electrons can only occupy specific orbits at specific energy levels around an atom. The farther away an electron is from the nucleus the higher it’s energy.

The Modern Atom Today’s atom is very similar to the Bohr atom. The modern atom is sometimes called the quantum mechanical atom. That is because the theory was based on a type of physics called quantum mechanics.

Quantum Mechanics Todays Atom is only different from Bohrs Atom in that it does not actually occupy orbits. It has a probability of occupying certain places around the atom and 90% of the time it spends in the ‘Bohr Orbits’. The position of the electron is determined by it’s energy.

Schrodinger The main mathematics for the quantum atom were performed by Erwin Schrodinger in the 20’s and 30’s. The equation that describes the position of an electron around an atom is called Schrodinger’s Equation and deals in differential calculus.

Neutron The Final sub-atomic particle was found in the 1930’s by James Chadwick. He proposed this particle had no charge but was as massive as the proton and also resided in the nucleus. He called it the neutron, after it’s neutral charge.

Today Today we think there are sub-sub- atomic particles called ‘quarks’. Each Proton, neutron and electron is made up of 3 quarks. Quarks come in many different types and have partial charges of 2/3 and -1/3. Quarks also have other properties named, strangness, charm, flavor, and color.