Models of Matter

What is a model?

A model is a simplified description of a complex thing.

F-16 Fighter

Model of a F-16 Fighter

But a model is not the real thing!

Size relative to the real thing.

Matter is anything that has mass and occupies space. Around 450 BCE, a Greek scholar named Empedocles proposed a model for matter. He thought that all matter was composed of four “elements”:

What is Matter?

For example, wood might be 2 parts earth, 2 part fire, and 1 part water. Volcanic rock might be 1 part

earth and 3 parts fire.

Matter is anything that has mass and occupies space. Around 450 BCE, a Greek scholar named Empedocles proposed a model for matter. He thought that all matter was composed of four ”elements”:

Models of Matter

earth air fire water

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For example, wood might be 2 parts earth, 2 part fire, and 1 part water. While volcanic rock might be

3 parts fire and 1 part earth.

http://www.oldgrowthagain.com/firewood2cordsm.jpg http://iceblog.puddingbowl.org/archives/120-2081_IMG-thumb.JPGEmpedocles

For example, wood might be 2 parts earth, 2 part fire, and 1 part water. Volcanic rock might be 1 part

earth and 3 parts fire.

Matter is anything that has mass and occupies space. Around 450 BCE, a Greek scholar named Empedocles proposed a model for matter. He thought that all matter was composed of four ”elements”:

earth air fire water

Matter is anything that has mass and occupies space. Around 450 BCE, a Greek scholar named Empedocles proposed a model for matter. He thought that all matter was composed of four “elements”:

http

://w

ww

.cwu.

edu/

~war

ren/

Uni

t1/E

mpe

docl

es.jp

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For example, wood might be 2 parts earth, 2 part fire, and 1 part water. While volcanic rock might be

3 parts fire and 1 part earth.

http://www.oldgrowthagain.com/firewood2cordsm.jpg http://iceblog.puddingbowl.org/archives/120-2081_IMG-thumb.JPGEmpedocles

Models of Matter

Aristotle was the most respected philosopher at about this time. He

preferred the model of Empedocles.For nearly 2000 years ,the “four elements” model was accepted.

Aristotle was the most respected philosopher at about this time. He

preferred the model of Empedocles.For the next 2000 years, the “four

elements” model was accepted.

Aristotle was the most respected philosopher at about this time. He

preferred the model of Empedocles.For the next 2000 years, the “four

elements” model was accepted.

About 50 years later, Democritus suggested a different model for matter. He thought that matter was made up of tiny, indivisible particles that he called atomos.

Democritus

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EmpedoclesAristotle

About 50 years later, Democritus suggested a different model for matter. He thought that matter was made up of tiny, indivisible particles that he called atomos.

Models of Matter

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Empedocles

Aristotle was the most respected philosopher at about this time. He

preferred the model of Empedocles.For nearly 2000 years ,the “four elements” model was accepted.

Aristotle was the most respected philosopher at about this time. He

preferred the model of Empedocles.For the next 2000 years, the “four

elements” model was accepted.

Aristotle was the most respected philosopher at about this time. He

preferred the model of Empedocles.For the next 2000 years, the “four

elements” model was accepted.

About 50 years later, Democritus suggested a different model for matter. He thought that matter was made up of tiny, indivisible particles that he called atomos.

Aristotle

About 50 years later, Democritus suggested a different model for matter. He thought that matter was made up of tiny, indivisible particles that he called atomos.

Models of Matter

In 1650, Robert Boyle rejected the “four elements” model. He redefined the term element to mean, any pure substance that cannot be chemically broken down into simpler substances. By the 1800’s, scientists had discovered many of these elements.

In 1650, Robert Boyle rejected the “four elements” model. He redefined the term element to mean, any pure substance that cannot be chemically broken down into simpler substances. By the 1800’s, scientists had discovered many of these elements.

In 1650, Robert Boyle rejected the “four elements” model. He redefined the term element to mean, any pure substance that cannot be chemically broken down into simpler substances. By the 1800’s, scientists had discovered many of these elements.

Models of Matter

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BoylePriestlyOXYGEN

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All matter is made of atoms.

Each element has its own kind of atom.

Compounds are created when atoms of different elements combine.

Atoms cannot be created or destroyed in chemical reactions.

In 1808, John Dalton proposed the atomic model for matter. The model states that:

Models of Matter

Dalton

In 1808, John Dalton proposed the atomic model for matter. The model states that:

To make a better model of the atom, scientists performed experiments. J.J. Thomson discovered that the atom contains very light, negatively charged particles (electrons). In Thomson’s “raisin bun” model, the atom is a positively charged sphere with embedded electrons.

To make a better model of the atom, scientists performed experiments. J.J. Thomson discovered that the atom contains very light, negatively charged particles (electrons). In Thomson’s “raisin bun” model, the atom is a positively charged sphere with embedded electrons.

To make a better model of the atom, scientists performed experiments. J J.J. Thomson discovered that the atom contains very light, negatively charged particles (electrons). In Thomson’s “raisin bun” model, the atom is a positively charged sphere with embedded electrons.

Models of Matter

Thomson cathode ray tube

A positive charge attracts the beamTherefore, the beam must be negatively charged.

A beam of particles can be made in this tube.

Raisin Bun model

+

-

+

-

Raisin Bun model

Thomson

positive sphere

negative electron

To make a better model of the atom, scientists performed experiments. J.J. Thomson discovered that the atom contains very light, negatively charged particles (electrons). In Thomson’s “raisin bun” model, the atom is a positively charged sphere with embedded electrons.

To be continued ...

In 1909, Ernest Rutherford devised an experiment to test Thomson’s “raisin bun” model. Rutherford knew that some elements released high-speed, positively charged particles, that he called alpha(α)particles.

Models of Matter

In 1909, Ernest Rutherford devised an experiment to test Thomson’s “raisin bun” model. Rutherford knew that some elements released high-speed, positively charged particles, that he called alpha(α)particles.

Rutherford

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positive sphere

negative electron

Models of MatterRutherford predicted that if α-particles were directed towards a very thin piece of gold foil, they would go straight through the atoms of gold.

α-pa

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The electrons might deflect the α-particle a bit, but the electrons do not have enough mass to have

much effect on the path of the α-particle.

Rutherford used polonium as a source of α-particles, a piece of gold foil and a detection screen that was coated with zinc sulfide, which produces a flash of light when the α-particle hits it.

Rutherford used polonium as a source of α-particles, a piece of gold foil and a detection screen that was coated with zinc sulfide, which produces a flash of light when the α-particle hits it.

Rutherford used polonium as a source of α-particles, a piece of gold foil and a detection screen that was coated with zinc sulfide, which produces a flash of light when the α-particle hits it.

Rutherford used polonium as a source of α-particles, a piece of gold foil and a detection screen that was coated with zinc sulfide, which produces a flash of light when an α-particle hits it.

lead box

α-particlespolonium

Models of Matter

zinc sulfide screen

flashesof light

gold foil

These are the expected results.

Gold Foil Experiment

These are the actual results.

Gold Foil Experiment

lead box

α-particlespolonium

zinc sulfide screen

flashesof light

gold foil

These are the actual results.

These results do not support the “raisin bun” model. There must be a small, dense, positively charged part of the atom. Rutherford realized that he had to change the model.

These results do not support the “raisin bun” model. There must be a small, dense, positively charged part of the atom. Rutherford realized that the model had to change.

These results do not support the “raisin bun” model. There must be a small, dense, positively charged part of the atom. Rutherford realized that he had to change the model.

Gold Foil Experiment

expected results for “raisin bun” model actual results

These results do not support the “raisin bun” model. There must be a small, dense, positively charged part of the atom. Rutherford realized that the model had to change.

Gold Foil ExperimentRutherford’s Nuclear Model

In Rutherford’s nuclear model, the atom is made of mostly empty space, with all of the positive charge and mass concentrated into a tiny nucleus. The position of the electrons are the same as Thomson’s model.

In Rutherford’s nuclear model, the atom is made of mostly empty space, with all of the positive charge and mass concentrated into a tiny nucleus. The position of the electrons are the same as Thomson’s model.

In Rutherford’s nuclear model, the atom is made of mostly empty space, with all of the positive charge and mass concentrated into a tiny nucleus. The position of the electrons are the same as Thomson’s model.

empty space

nucleus

electrons

Nuclear model

Bohr-Rutherford Model

Bohr-Rutherford model

Niels Bohr improved Rutherford’s model by showing that electrons travel around the nucleus in circular paths called orbits.

The evidence for this comes from emission spectra. These are a kind of light “fingerprint” that can be used to

identify elements.

Bohr

Rutherford’s Nuclear Model