WHAT IS MATTER MADE OF?

1. Fire, air, water and earth

5 THEORIES OF MATTER

2. Tiny, solid particles called atoms

3. Lumps of positively charged material with negative electrons all through it

5. A positive nucleus with electrons orbiting around it

3. A positive nucleus with negative electrons moving around it

WHAT IS MATTER MADE OF?

• Empedocles was a Greek philosopher and scientist

• He said that matter is made of:

Why might that make sense to

people who knew nothing about atoms?

SO WHAT IS MATTER MADE OF?

John Dalton, who lived in the early 1800s, said:

1. Matter is made up of tiny particles called atoms

2. Atoms can’t be created, or destroyed

3. All atoms of the same element are identical and are different from atoms of all other elements

4. Different elements link together, in defined whole number ratios, to make compounds

Dalton’s atom

Atoms are the smallest particles and don’t have distinct parts

1. Matter is made up of tiny particles called atoms

John Dalton, who lived inthe early 1800s, said:

http://www.youtube.com/watch?v=1xSQlwWGT8M&feature=fvwrel

Introduction to the Atom @ http://www.khanacademy.org/

Dalton also said: 2. Atoms cannot be created or destroyed

Hydrogen

Sodium

Lithium UraniumGold

3. All Elements have Unique Atoms

Dalton also said:

Dalton also said:2.

Dalton also said:4. Elements combine in defined, whole number ratios

H2O – water vs. not H2O – water

hydrogen

oxygen

hydrogen

oxygen

hydrogen hydrogen

oxygen oxygen

¾ oxygen

hydrogen½ hydrogen

hydrogen

oxygen

½ hydrogen

Dalton also said:3.

Joseph John Thomson in 1897:

1. Discovered that atoms have negatively charged particles in them

2. Concluded that since atoms are neutral they must also contain positive particles to balance the negatively charged particles

3. Proposed that the atom is a lump of positively charged material with negative electrons all through it

your textbook’s version

Thomson’s atom

positive materialnegative electrons

Atoms aren’t the smallest particles and do have distinct parts; a positive body and electrons

Production of Cathode Rays

To Vacuum Pump

Anode

Green GlowAir at Very Low Pressure

Cathode

Discharge Tube

How Thomson Found Negative Particles

1. He used a cathode ray tube like these ones

2. The tubes contain small amounts of gas

3. He used electricity to run a current through the gas in the tube

4. The gas glowed

5. The glow started from the negative end and went to the positive end

6. Opposites attract so if the glow moved towards the positive end that meant it must have been negative

7. That meant some kind of negative things from the atoms were moving

8. We now call these particles electrons

High voltage Generator

Production of Cathode Rays

To Vacuum Pump

Anode

Green GlowAir at Very Low Pressure

Cathode

Discharge Tube

High voltage Generator

Production of Cathode Rays

Green Glow Starts Here Green

Glow Moves to Here

Green Glow Direction

Green Glow Direction

Thomson’s Cathode Ray ExperimentEvidence of Electrons

Ernest Rutherford’s 1907 study of atomic structure:

1. He fired very tiny, fast, positive alpha particles at a very thin sheet of gold foil

2. He expected the alpha particles to just pass straight through the spaces between the particles in the foil

3. Some passed straight through, some veered off on angles, and some bounced back

4. He concluded that atoms must have a positive core that the alpha particles were hitting

5. He named this core the nucleus and proposed that the electrons revolved around the nucleus

Rutherford’s atom

positive nucleus

revolving electrons

Atoms aren’t the smallest particles and do have distinct parts; a positive nucleus and electrons

Rutherford’s Gold Foil Experiment

Apparatus for experiment Path of alpha (α) particles

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Fast-moving positive particles Gold foil atoms

Niels Bohr’s Question

1. Positive and negative charges are attracted to each other

2. Atoms contain positive protons and negative electrons

3. The electrons and protons in an atom are not drawn in towards each other

Q. Why don’t atoms collapse?

Why don’t atoms collapse?

Niels Bohr in 1912

1. Something must be keeping the electrons from collapsing into the nucleus

2. He determined that electrons only move in defined orbitals around the nucleus

3. For electrons to move between orbitals they need specific amounts of energy

4. He called these bundles of energy quanta

Bohr-Rutherford atom

Atoms have distinct parts; a positive nucleus and electrons that move around it in orbitals

1.Dalton’s

atom

2. Thomson’s

atom

3. Rutherford’s

atom

4.Bohr-Rutherford

atom

Evolution of the Atomic Modelto be continued …