Download 4.1 Studying the Atom Notes

Unit 4.1.doc
4-1 Properties of Elements Relate to the Atomic
Structure
History of the Atom: http://www.youtube.com/watch?v=njGz69B_pUg
HOW DO WE STUDY SOMETHING WE CAN NOT SEE?

Ancient Greeks and Romans
o Earth
o Wind
o Fire
o Water
 400 BC Greeks proposed some ideas of matter.
o All things are made of “atoms” ***
o Atoms are indivisible
o Atoms are very small
*** The word “atom” comes from Greek.:
About 2500 years ago the Greek
philosopher/scientist Democritus came up with the idea that the world must be made up of really small
particles that he thought could not be split. So he called them atoms form the Greek word atomos which
means 'that which can not be split.' Of course, he was only about 90% right.
No real advancements in these ideas for more than 2000 years
 Chemists in the 1700’s advanced the following ideas
o Law of Definite Composition
 Like compounds are made of atoms of the same element
combined in the same proportions
 Example : Water is 2 parts H and 1 part O
o Law of Conservation of Mass
 When chemicals react no mass can be created or destroyed.
Or “The atom in the substance you start with must be the
atoms that make what you end up with.”
o
Law of Multiple Proportions
 Atoms Combine in Whole Number Ratios – there is no such
thing as a fraction of an atom.
DALTON’S ATOMIC THEORY
John Dalton (early 1800’s) realized the importance of these ideas. He improved upon these
ideas.
1st Atomic Theory
Principle
T/F
All matter is made of indivisible and indestructible atoms.
Atoms of the same element are identical.
Atoms of different elements are different.
Atoms combine in whole number ratios.
Atoms cannot be created or destroyed.
How many of these turn out to be true?
John Dalton - credited with the first Atomic Theory.
You don’t need to write this.
 Other chemists of the time tested the theory
 Few exceptions to the Theory.
 Even with the exceptions, this theory has been used,
advanced and modified.
Scientists find Atom is not Indivisible
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Work with cathode tube shows electrical nature of atom
Parts are electrically charged.
Implying some parts are negatively and positively charged.
Electrons were randomly said to be negative.
CRT Experiments :
Other: http://www.youtube.com/watch?v=RW_zfKOU9uM
Sydney -http://www.youtube.com/watch?v=2xKZRpAsWL8
Thomson Model of the atom (from CRT)– Plum pudding Model
Rutherford’s Gold Foil
Experiment
1. MATTER IS MADE UP MOSTLY OF EMPTY
SPACE
2. PROVED SEPARATION BETWEEN + AND –
3. Some particles bounced back. – confirmed
the existence of the Nucleus (means “ little nut”)
Gold Foil Experiment: http://www.youtube.com/watch?v=5pZj0u_XMbc
This lead to the Bohr Model of the atom –