History of the Atom Webquest!

Name:______Date:______Period:____

History of the Atom Webquest!

Democritus (~400 B.C.E.)

1. What 4 elements did people at this time believe that all matter is made up of?

Fire, air, water, and earth

2. What did Democritus call the tiny fundamental particles of matter?

atomos

3. What did Democritus’s model look like?

John Dalton (1766-1844)

1. What were the most important points in Dalton’s atomic theory?

1. All matter is made of atoms, which are indivisible
2. All atoms of a given element are identical in mass and properties
3. Compounds are combinations of 2 or more different types of atoms
4. A chemical reaction is a rearrangement of atoms

1. What 2 laws were Dalton’s theory based on?

Law of conservation of mass

Law of definite proportions (or constant composition)

1. What does the law of conservation of mass say?

Matter is not created or destroyed in a closed system

1. What does the law of definite proportions say?

In a pure compound, there will always be the same proportion of the same elements

For example, table salt, which has the molecular formulaNaCl, contains the same proportions of the elements sodium and chlorine no matter how much salt you have or where the salt came from

1. Which points have been proven false?

Atoms are not indivisible—as stated in part one—because they are made up of protons, neutrons, and electrons

1. Draw/Describe a model for Dalton's atom.

J.J. Thomson (1856-1940)

Dalton’s atomic model help up for a good hundred years until J.J. Thomson did some experiment with his newly discovered “cathode rays.”

1. What is the name of Thomson’s experiment?

Cathode Ray Experiment

1. Describe Thomson’s experiment. Draw a picture, if it helps.

1. What subatomic particle did Thomson find?

electrons

1. What is the name of Thomson’s model?

Plum-pudding model

1. Sketch Thomson’s model. Be sure to label the parts.

Ernest Rutherford (1871-1937)

1. Describe Rutherford’s experiments with gold foil

1. What were 2 of Rutherford’s discovery in the atom? How did he determine these?

The positive charge must be localized over a very tiny volume of the atom, which also contains most of the atom's mass. This explained how a very small fraction of thealphaparticles were deflected drastically, presumably due to the rare collision with a gold nucleus.

AKA: positive nucleus

Since most of thealphaparticles passed straight through the gold foil, the atom must be made up of mostly empty space!

1. Draw a diagram of what happened to the alpha particles when passing (or bouncing back) through the gold foil.

1. Draw a model for Rutherford’s atom

James Chadwick (1932)

1. What did Chadwick find in the atom?

Neutrons

Niels Bohr (1885-1962)

1. Describe Bohr’s model of the atom.