Download I. Ch. 3.1: Democritus and Dalton

Unit 3 (pt. 1) guided Notes
I.
Ch. 3.1: Democritus and Dalton
A.
The Atom: A Philosophical Idea
1.
The idea of __________________ is very old.
2.
Democritus (Greek, 400 BC) - said that things were made up of tiny,
indivisible particles (atoms) – only an idea
3.
Aristotle - disagreed with Democritus’ idea – his opinion was more
___________________, so the concept of atoms was lost until John Dalton.
4.
B.
No evidence to support either idea.
Three Fundamental Laws of Chemistry
1.
Law of Conservation of Mass (1789):
a)
In ordinary chemical reactions, mass is neither ______________ nor
___________________.
b)
Mass of the reactants equals the mass of the products (as does # of
atoms).
2.
Law of Definite Proportions (1797):
a)
A chemical compound contains the same elements in exactly the same
proportions regardless of the size of the sample or source of the compound.
b)
3.
Example: water – hydrogen to oxygen ratio is always _____________.
Law of Multiple Proportions (1803):
a)
If two or more different compounds are composed of the same two
elements, then the proportions can be expressed as simple, whole-number
ratios.
b)
Example:
(1)
Carbon and Oxygen
(a)
Carbon monoxide - CO
(b)
C.
Carbon dioxide – CO2
John Dalton (1808)
1.
English __________________ __________________________, wanted to explain the
laws of conservation of mass, definite proportions and multiple proportions.
2.
His model is called Dalton’s Atomic Theory.
3.
Postulates of his theory
a)
All matter is composed of extremely small particles called __________.
b)
Atoms of a given element are identical in size, mass, and other
properties; atoms of different elements differ in size, mass, and other
properties.
c)
Atoms cannot be subdivided, created, or destroyed.
d)
Atoms of different elements combine in simple whole-number
___________ to form chemical compounds (molar ratios).
e)
In chemical reactions, atoms are combined, separated, or rearranged.
4.
Some aspects of Dalton’s atomic theory have been revised. We now
know that:
D.
II.
a)
Atoms are divisible into even smaller particles.
b)
A given element can have atoms with different _____________.
Reflection
Ch. 3.2: Models of the Atom
A.
Warm up: Friday, September 27
1.
Create a drawing that illustrates Dalton’s view of an atom.
2.
Based on what you learned about atoms in other science classes, create
a diagram that represents the structure of an atom.
3.
Explain how your two drawings are different.
B.
Today’s Objectives:
1.
Recognize that science is a progressive endeavor that reevaluates and
extends what is already known. (SPI 3221. Inq.1)
2.
Identify the contributions of major atomic theorists: Dalton, Thomson,
Rutherford, and Bohr. (SPI 3221.1.1)
3.
C.
Compare and contrast historical models of the atom. (SPI 3221.1.2)
JJ Thomson – 1897
1.
He discovered that within atoms there are negatively charged particles
2.
He called these particles ____________________.
a)
Thomson performed experiments that involved passing electric
current through gases at low pressure.
b)
3.
The result was a glowing beam called a _______________ _________.
A cathode ray is deflected by electrically charged plates.
4.
Thomson concluded that a cathode ray is a stream of electrons.
Electrons are parts of the atoms of all elements.
5.
From his findings, Thomson developed the “Plum pudding” model.
a)
The atom was filled with positively charged material and the electrons
were evenly distributed throughout.
D.
Ernest Rutherford - 1911
1.
Gold foil experiment
2.
He directed a narrow beam of alpha particles at a very thin sheet of
gold foil.
3.
Alpha particles are positively charged particles that are released by
certain radioactive elements as they decay.
4.
Rutherford’s Gold-Foil Experiment
a)
Alpha particles scatter from the gold foil.
b)
The Rutherford Atomic Model
(1)
Rutherford concluded that the atom is mostly _____________
__________.
(2)
All the positive charge and almost all of the mass are concentrated in
a small region in the center of the atom.
(3)
E.
He called this tiny core the _________________.
Niels Bohr- 1913
1.
Planetary Model
2.
Electron is found only in specific circular paths, or ________________,
around the nucleus.
F.
Reflection