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History of the Atom Timeline Worksheet key, Exercises of Chemistry

History of the Atom proposed by John Dalton, J. J. Thompson, Lord Ernest Rutherford, Niels Bohr

Typology: Exercises

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Name: _________________________________ Date: __________ Class: _______
John Dalton (1766 1844):
John Dalton was an English chemist. His ideas form the atomic theory
of matter. Here are his ideas.
All elements are composed (made up) of atoms. It is impossible
to divide or destroy an atom.
All atoms of the same elements are alike. (One atom of oxygen
is like another atom of oxygen.)
Atoms of different elements are different. (An atom of oxygen is different from an atom of hydrogen.)
Atoms of different elements combine to form a compound. These atoms have to be in definite whole number ratios.
For example, water is a compound made up of 2 atoms of hydrogen and 1 atom of oxygen (a ratio of 2:1). Three atoms
of hydrogen and 2 atoms of oxygen cannot combine to make water.
1. What is the name of John Dalton’s theory? THE ATOMIC THEORY OF MATTER
2. What are elements made of? ELEMENTS ARE MADE OF ATOMS
3. An atom of hydrogen and an atom of carbon are DIFFERENT
4. What are compounds made of? COMPOUNDS ARE MADE OF ATOMS OF TWO OR MORE DIFFERENT ELEMENTS
5. The ratio of atoms in HCl is: a) 1:3 b) 2:1 c) 1:1
6. The ratio of atoms in H2O is: a) 1:3 b) 2:1 c) 1:1 2 atoms of hydrogen and 1 atom of oxygen
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Name: _________________________________ Date: __________ Class: _______

John Dalton (1766 – 1844):

John Dalton was an English chemist. His ideas form the atomic theory

of matter. Here are his ideas.

 All elements are composed (made up) of atoms. It is impossible

to divide or destroy an atom.

 All atoms of the same elements are alike. (One atom of oxygen

is like another atom of oxygen.)

 Atoms of different elements are different. (An atom of oxygen is different from an atom of hydrogen.)

 Atoms of different elements combine to form a compound. These atoms have to be in definite whole number ratios.

For example, water is a compound made up of 2 atoms of hydrogen and 1 atom of oxygen (a ratio of 2:1). Three atoms

of hydrogen and 2 atoms of oxygen cannot combine to make water.

1. What is the name of John Dalton’s theory? THE ATOMIC THEORY OF MATTER

2. What are elements made of? ELEMENTS ARE MADE OF ATOMS

3. An atom of hydrogen and an atom of carbon are DIFFERENT

4. What are compounds made of? COMPOUNDS ARE MADE OF ATOMS OF TWO OR MORE DIFFERENT ELEMENTS

5. The ratio of atoms in HCl is: a) 1:3 b) 2:1 c) 1:

6. The ratio of atoms in H 2 O is: a) 1:3 b) 2:1 c) 1:1 2 atoms of hydrogen and 1 atom of oxygen

J. J. Thompson (Late 1800s): J. J. Thompson was an English scientist. He discovered the electron when he was experimenting with gas discharge tubes. He noticed a movement in a tube. He called the movement cathode rays. The rays moved from the negative end of the tube to the positive end. He realized that the rays were made of negatively charged particles – electrons.

  1. What did J.J. Thompson discover? J.J. THOMPSON DISCOVERED THE ELECTRON
  2. What is the charge of an electron? ELECTRONS ARE NEGATIVELY CHARGED
  3. What are cathode rays made of? CATHODE RAYS ARE MADE OF ELECTRONS
  4. Why do electrons move from the negative end of the tube to the positive end? BECAUSE ELECTRONS ARE NEGATIVE, AND NEGATIVE CHARGES ARE ATTRACTED BY POSITIVE CHARGES
  5. What was Thompson working with when he discovered the cathode rays? HE WAS EXPERIMENTING WITH GAS DISCHARGE TUBES For more information https://www.youtube.com/watch?v=4QAzu6fe8rE Thomson’s Experiment https://www.youtube.com/watch?v=F0I-11R_IHg Experimento de J.J. Thomson

Lord Ernest Rutherford (1871 – 1937): Ernest Rutherford conducted a famous experiment called the gold foil experiment. He used a thin sheet of gold foil. He also used special equipment to shoot alpha particles (positively charged particles) at the gold foil. Most particles passed straight through the foil like the foil was not there. Some particles went straight back or were deflected (went in another direction) as if they had hit something. The experiment shows:Atoms are made of a small positive nucleus; positive nucleus repels (pushes away) positive alpha particlesAtoms are mostly empty space

  1. What is the charge of an alpha particle? ALPHA PARTICLES ARE POSITIVELY CHARGED
  2. Why is Rutherford’s experiment called the gold foil experiment? BECAUSE IN HIS EXPERIMENT HE USED A THIN SHEET OF GOLD FOIL
  3. How did he know that an atom was mostly empty space?

BECAUSE MOST PARTICLES PASSED STRAIGHT THROUGH THE FOIL LIKE THE FOIL WAS NOT THERE

  1. What happened to the alpha particles as they hit the gold foil?

MOST PARTICLES PASSED STRAIGHT AND SOME PARTICLES WENT STRAIGHT BACK OR WENT IN ANOTHER DIRECTION

  1. How did he know that the nucleus was positively charged?

BECAUSE THE NUCLEUS REPELLED THE ALPHA PARTICLES, AND PARTICLES REPEL WHEN THEY HAVE THE SAME CHARGE.

For more information https://www.youtube.com/watch?v=XBqHkraf8iE https://www.youtube.com/watch?v=IQ1h_gdVlHg https://www.youtube.com/watch?v=Pc0LWkUWPI