Download Lesson 5

Review:
­ physical properties
­ chemical properties
Sep 21­3:27 PM
Theory and Law
­ a theory is an idea that is proposed and that can change over a period of time
­ for example Darwin's theory of evolution continues to change as more evidence is found (fossils, new species, etc)
­a law is a pattern or relationship that can be proven repeatedly
­ for example the law of gravity is constant and is proven everytime something falls on the floor
Sep 21­3:44 PM
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Theory or Law?
­ place each idea below in the theory or law category
LAW
THEORY
Scientists can clone dinosaurs
Aliens live on other planets
Water freezes at 100 C
Clouds form due to evaportation
Space has no end
Trees use carbon dioxide
Dogs are smarter then cats
Tin is malleable
Sep 27­7:24 PM
The Atom
­ today we know that all matter is composed of atoms
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atoms are composed of protons, neutrons electrons
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the center of an atom is a nucleus and it contains the protons and neutrons
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electrons circle the nucleus in different orbits depending on the atom
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a neutral atom has the same number of electrons and protons
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proton number is the atoms atomic number
(How do we know all this???)
Sep 27­7:53 PM
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Development of Atomic Theory
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the information we know about the atom is known as the atomic theory
­ the atomic theory has not always remained the same
­ since it is a theory it has changed and developed as new scientists have come on the scene
Sep 27­7:51 PM
(1) Early Greeks (Empedocles, Democritus, Aristotle)
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2500 years ago Empedocles claimed matter was made up of four elements: earth, air, wind and fire
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Democritus said that any object cut into smaller pieces would eventually become so small that it could not be cut any more (called this smallest piece atomos)
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Aristotle agreed with Empedocles and this idea became accepted for the next 2000 years
(yikes)
Sep 27­7:58 PM
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There are only 4 elements and that's the bottom line because Aristotle said so!!
Sep 27­8:06 PM
2. John Dalton (1766 ­ 1844)
­ his theory is often called the billard ball model because he saw the atom as being the same throughout and being indivisible
Each atom is the same throughout but diffent from other atoms, like these billard balls.
Sep 27­8:08 PM
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Dalton created his atomic theory:
(a) all matter is made up of small particles called atoms
(b) atoms cannot be created, destroyed or divided into smaller particles
(c) all atoms of the same element are identical but they are different then the atoms of another element
(d) compounds are created when atoms of different elements are joined
Sep 27­7:48 PM
3. J.J Thomson (1856 ­ 1940)
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his theory is often called the raisin bun model
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he saw the negative electrons scattered throughout the positive area of the atom like raisins are scattered through a bun
Just like a raisin
bun
Sep 27­8:20 PM
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4. Ernest Rutherford (1871 ­ 1937)
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his theory is called the planetary model
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he saw electrons circling the center of the atom like planets circle the sun
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proposed that the atom is mostly empty space with a very small and heavy nucleus
Oct 1­10:03 AM
Rutherford Model
Electrons circle the nucleus
Oct 1­10:07 AM
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5. Niels Bohr (1885 ­ 1962)
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built on the Rutherford model
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he believed that the electrons did circle the nucleus but did so at different energy levels (shells)
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each energy level could only contain a certain number of electons
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the Bohr model he created is the accepted model for the atom today
Oct 1­10:09 AM
Bohr Model
My model is the best
Oct 1­10:14 AM
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Readings
Pages 24 ­ 29
Questions:
Page 29, #'s 2,3,4,5,6,7,
Oct 1­10:15 AM
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