Transcript Chemistry Chapter 4 - Manistique Area Schools

Chemistry
Chapter 4
Notes #1
09/10/10
Democritus





Matter is composed of empty space where atoms
move
Atoms are solid, homogenous, indivisible, and
indestructible
Different types of atoms have different sizes and
shapes
Differing properties of matter are due to the size,
shape, and mvmt of atoms
Apparent changes in matter result from changes in
the groupings of atoms and not in changes in the
atoms themselves
Democritus




1st person to believe that matter was not
infinitely divisible
Just ideas – no science (proof)
460 – 370 BC
Completely rejected by Aristotle (did not
believe in atoms)
John Dalton




1766-1844
English School Teacher
Used science to prove Democritus’ ideas
Beginning of modern atomic theory
John Dalton






All matter is composed of very small particles
(atoms)
All atoms of a given element are identical
(having same mass, size, and properties)
Atoms of a specific element are different from those
of any other element
Atoms cannot be created or destroyed or
divided into smaller particles
Different atoms combine in simple whole number
ratios to form compounds
In a chemical reaction, atoms are separated,
combined, or rearranged
Since Dalton….


Modern atomic theory has been refined
“Atom”

Smallest particle of an element that retains the
properties of that element
Sir William Crookes



Cathode ray – typical set up used to study
mass and charge of particles
Crookes noticed flashes of light (radiation)
He tested and proved



Cathode rays were a steam of charged particles
The particles had a negative charge
After changing the electrodes and the gas in the
tubes, the ray was still present, indicating that
these particles were in all matter
JJ Thomson & Robert Millikan


Continued with Crookes work
Found that the mass of these particles was less
than that of Hydrogen





What did this mean?
Something smaller than the atom!
Atoms are divisible
Millikan did work at the same time – said these
particles were negative – called them electrons
Thomson Proposed the Plum Pudding Model

Positive atom with evenly dispersed negative
Ernest Rutherford


Disproved the plum pudding model with the gold foil
experiment
Rutherford set forth the idea of the nuclear atom
(with a dense center)






He called it a “nucleus”
It has a positive change
Almost all of the atom’s mass
Negatives charges surround the nucleus – held together by
attraction between pos. & neg.
8 years later = protons (1920)
1932 – his coworker (Chadwick) discovered
neutrons
Neils Bohr

In atomic physics, the Bohr model depicts
the atom as a small, positively charged
nucleus surrounded by electrons that travel in
circular orbits around the nucleus — similar in
structure to the solar system, but with
electrostatic forces providing attraction, rather
than gravity.