3-2: Discovering Atomic Structure

By Ms. Pacheco

Michael Faraday

• 1839 (English)

• Faraday suggested that atoms of different elements behave differently due to electricity, though he didn’t know exactly how

• He was right; atoms contain particles that have an electric charge

Ben Franklin

• Faraday wasn’t the first to study electricity, though

• Franklin was a statesman and a scientist

• Famous for his kite and key experiment

• Said that objects had either a positive or negative charge

• Like charges repel; opposite charges attract

A statue of Franklin at the University of Philadelphia

Franklin was also…• An inventor

• A printer

• A philosopher

• A musician

• An economist

• The only person to sign– The Declaration of Independence– The Treaty and Alliance of France– The Treaty of Paris– The Constitution

One last note on Franklin…

• He loved turkeys• He even used them

in his experiments with electricity!!!!!

• He actually wanted the national bird to be a turkey!

• Ben Franklin On The Turkey As National Bird• "For my own part I wish the Bald Eagle had not been chosen the

Representative of our Country. He is a Bird of bad moral Character. He does not get his Living honestly. You may have seen him perched on some dead Tree near the River, where, too lazy to fish for himself, he watches the Labour of the Fishing Hawk; and when that diligent Bird has at length taken a Fish, and is bearing it to his Nest for the Support of his Mate and young Ones, the Bald Eagle pursues him and takes it from him.

• "With all this Injustice, he is never in good Case but like those among Men who live by Sharping & Robbing he is generally poor and often very lousy. Besides he is a rank Coward: The little King Bird not bigger than a Sparrow attacks him boldly and drives him out of the District. He is therefore by no means a proper Emblem for the brave and honest Cincinnati of America who have driven all the King birds from our Country....

• "I am on this account not displeased that the Figure is not known as a Bald Eagle, but looks more like a Turkey. For the Truth the Turkey is in Comparison a much more respectable Bird, and withal a true original Native of America... He is besides, though a little vain & silly, a Bird of Courage, and would not hesitate to attack a Grenadier of the British Guards who should presume to invade his Farm Yard with a red Coat on."

• --Benjamin Franklin, in a letter to his daughter

Can you imagine?!?

J.J. Thomson

• 1896 (English scientist)

• Using cathode ray tubes, discovered that atoms contained a negatively charged particle that he will call the electron

Robert Millikan

• 1909 (American physicist)

• Using an oil drop experiment, calculated the charge and mass of a single electron

Henri Becquerel

• 1896 (French physicist)

• Accidentally discovered radioactivity (the emission of radiation from an element)

Becquerel’s First Radiograph

Becquerel’s worked with and shared the 1903 Nobel Prize in

Physics with…

Pierre and Marie Curie

• Both would later die from exposure to radiation

Ernest Rutherford

• 1909 (New Zealand scientist)

• Performed an alpha scattering experiment, using gold foil

Ernest Rutherford

• Proved the existence of a positively changed particle in an atom, that he called a proton

• Said that the core of the atom (he called the nucleus) contains all of the mass and all of the positive charge

Niels Bohr

• Danish (1913): – electrons travel

around the nucleus in orbits (sun-planet model)

– Electrons could drop from higher energy level to a lower energy level, emitting

First X-ray (1896)