Atomic Theory and the Models of the Atom

He was a very famous Greek philosopher who believed that matter could be divided into smaller and smaller pieces forever.

He proposed that matter was made of small units called “atomos” that were indivisible.

He explained that the atom is the smallest particle that an element can be divided & still be the same substance.

He stated that all matter flows continuously and is composed of 4 elements - fire, air, earth and water

John Joseph Thomson found that atoms could sometimes eject a far smaller negative particle which he called an ___________.

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He suggested that atoms are like tiny spheres, so he used wooden spheres to model them.

This is the Bowling Ball or Billiard Ball Model of the Atom.

In the cathode ray tube experiment where the presence of negative particle was deduced, what as observed?

• Adding an electric field cause the beam to bend and move toward the positive plate.

• Adding an electric field cause the beam to bend and move toward the negative plate.

• Adding a magnetic field cause the beam to bend and move toward the positive plate.

• Adding a magnetic field cause the beam to bend and move toward the negative plate.

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JJ Thomson also predicted that there also must be ________ particles to hold the electrons in place. He

He proposed the Plum Pudding or Raisin Bread Model of the Atom.

In the Gold Foil Experiment conducted by Ernest Rutherford, he concluded that the atom is mostly empty space. What was his observation?

• He observed that most alpha particles went straight through the gold foil.

• He observed that most alpha particles were deflected by the gold foil.

• He found the gold foil lost its luster.

• He observed that the electric field caused the alpha particle to move toward the positive plate.

Ernest Rutherford discovered the atom has a ________ with positively charged particles and the electrons must be “floating” around it.

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NGSS.HS-PS1-8

James Chadwick discovered that ________ were also located in the nucleus of an atom and that they contain no charge.

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