Atomic Structure.

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Presentation transcript:

Atomic Structure

Hypothesis – First Models Of Matter There were many scientist that contribute to the development of the first models of matter They Included: Aristotle Democritus John Dalton 4. J.J. Thomson 5. Rutherford 6. Bohr

Father of the Atomic Theory Dalton’s Atomic Model Even today, basic principles of his theory are still true. His model was modified to explain new observations of later chemists Father of the Atomic Theory

Atomic Theory Developed by John Dalton He is known as the father of the Atomic Theory. He formulated four main points concerning atoms: Memorize All matter is composed of tiny indivisible particle called atoms. All atoms of the same element are identical (same). Atoms of different elements are different. During a chemical reaction atoms combine to form new products.

J.J. Thomson’s Atomic Model Thomson discovered the electron while experimenting with cathode rays. - Electrons have a negative charge Thomson believed: The atom was a positive sphere with electrons embedded in it like raisins in a plum pudding. It looks like a chocolate chip cookie!!!

Cathode Rays A cathode ray tube is a sealed evacuated glass tube. Cathode rays are beams of tiny, negatively charged particles called electrons that flow through this tube. J.J Thompson used these tubes to discover the various properties of cathode rays (electrons)

Properties Of Cathode Rays Memorize Properties Of Cathode Rays 1. The cathode rays travel in a straight line. 2. The cathode rays drive a small propeller located in their path. This tells us that cathode rays have mass.

Properties Of Cathode Rays continued... Properties Of Cathode Rays 3. The cathode rays cause the shadow of the object in their path to be projected on a fluorescent screen.

4. The cathode rays are deflected towards the positively charged continued... Properties Of Cathode Rays 4. The cathode rays are deflected towards the positively charged plate. This tells us that cathode rays are negative.

RUTHERFORD’S ATOMIC MODEL Ernest Rutherford also developed his own atomic theory HE BELIEVED: the atom had a central positive nucleus surrounded by negative electrons floating around in a cloud like structure

Rutherford’s Atomic Model Rutherford used the ideas of radioactivity to carry out experiments to help him better define the atomic model. His experiment involved: Exploring matter by shooting alpha particles against thin sheets of metal.

SEVERAL particles pass through the A FEW particles are sharply deflected SEVERAL particles pass through the gold foil & were slightly deflected Alpha Particle beam Thin sheet of Gold foil Radium in Lead Block MOST particles passed through the gold foil & were not deflected Fluorescent Screen Fluorescent Screen

Conclusions from Rutherford’s Experiment: Alpha Particles MOST went through empty space Conclusions from Rutherford’s Experiment: FEW approach nucleus & bounced back Gold Atom 3 Main Observations SEVERAL were deflected by the nucleus OBSERVATIONS CONCLUSIONS 1. MOST (almost all) went through the gold foil & were not deflected Atom contains a significant amount of empty space 2. FEW (not many) bounced directly back The atom’s dense core (nucleus) must be very small 3. SEVERAL (some) passed through the gold foil & were deflected The nucleus must be positive (law of repulsion)

placed electrons orbiting, Rutherford Model Rutherford proposed a new model based on his findings and Thomson's Model. Rutherford’s Model placed electrons orbiting, like a cloud, around a dense, positively charged nucleus. Nucleus Electrons

EX# 5 Rutherford Thomson EX# 6 Which diagram is Thompson’s and which diagram is Rutherford’s? _ _ _ _ + _ Rutherford + _ + + _ _ + _ + _ + _ _ Thomson EX# 6 Rutherford believed the nucleus was POSITIVE or NEGATIVE?

Bohr – Rutherford Atomic Model: NEIL BOHR proposed modification to Rutherford Model proposed that electrons can only circle the nucleus at very specific distances (called orbits) Bohr & Rutherford combined theirtheories to create the current simplified atomic model

Key Points to Remember Thomson’s Model is known as the plum pudding model. He also discovered the electron. Rutherford’s Model Positive nucleus surrounded by a fuzzy cloud Electrons not organized

Key Points to Remember Bohr – Rutherford Model states that here is a nucleus that is surrounded by orbits (energy shells)