Download chapter four: the structure of the atom

CHAPTER FOUR:
THE STRUCTURE OF THE ATOM
The Atom
Smallest particle of an element that retains the properties of that element
* made of much smaller particles
* our concept is a result of generations of work
Early atomic theory begins with...
Democritus
* 400 BC
* Claimed the world was nothing but empty space and atoms
"All matter is made of very small particles ­­ much too small to see."
atomos: indivisible
* different types of atoms = different sizes, shapes and movement =
different types of properties
* believed that atoms could not be created, destroyed or further divided.
Aristotle *criticized Democritus*
(384­322 BC)
*thought the world was made of "hyle" (continuous matter)
*Did NOT believe in atoms
*Thought all matter was continuous
* He couldn't wrap his mind
around the concept of
empty space!
Aristotle believed that
matter is made of...
But really, what did it matter what philosophers thought when they had no experimental data to support their ideas?
Improved balances helped scientists accurately measure
masses of elements and compounds. This lead to several laws:
1. Law of Conservation of Mass
2. Law of Definite Proportions
3. Law of Multiple Proportions
Law of Conservation of Mass
Mass is neither created nor destroyed during ordinary chemical reactions or physical changes
2H2O 100.00g
11.21g
H
H
2H2 + O2
O
H
88.79g
H
O
O
H
H
H
O
H
Antoinne LaVoisier
Law of Definite Proportions
Proust
A chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound
H2O
2:1
Not to be confused with THE LAW OF MULTIPLE PROPORTIONS
2 or more different compounds can be composed of the same elements
H2O
vs
H­2O2
water vs. hydrogen peroxide
CO
vs carbon monoxide vs. carbon dioxide
CO2
John Dalton
* 1800's
* Studied experiments of others
* Came up with a feasible theory about atoms
The Atom: smallest particle of an element that retains the
properties of the element.
Dalton's Atomic Theory
1. All matter is made of atoms.
2. All atoms of the same element are identical.
3. Atoms of different elements are not alike.
4. Atoms can combine in simple, whole number ratios to form compounds (Law of multiple proportions). 5. Atoms cannot be subdivided, created or destroyed.
CO molecules on Pt
Made with atomic force microscope
Xe on nickel
Scanning Tunneling Microscope
Iron on copper
Nanotechnology