Transcript The Atom - Effingham County Schools

Atomic Timeline
WARM-UP: Take out your Ch. 3 VOCABULARY and timeline materials and
begin completing timeline.
• With your table, you are to create an Atomic
Discovery Timeline/Historical Collage that
•Each person or
includes the following:
•
•
•
•
•
•
•
•
•
Democritus
Aristotle
Law of Conservation of Mass
Law of Definite Proportions
Law of Multiple Proportions
John Dalton
Joseph Thompson
Robert Millikan
Ernest Rutherford
discovery should be on
one piece of paper and
include a summary,
date, and illustration
Compound
Mass of nitrogen that
combines with 1 g oxygen
NO
1.70
NO2
0.85
NO4
0.44
• NO
• N:O
• 1:1
1.7g :1 g
NO2
N:O
1:2
(8.5 x 2)= 1.7
1.7g : 2g
Compound
Mass of nitrogen that
combines with 1 g oxygen
NO
1.70
NO2
0.85
NO4
0.44
NO2
 N:O
 1:2
(2x.85) =1.7
1.7 g : 2 g

NO4
N:O
1:4
(.44 x 4) =1.76
1.76 to 4 g
August 23
WARM UP: Find the ratio of N :O
Compound
Mass of nitrogen that
combines with 1 g oxygen
NO
1.70
NO2
0.85
NO4
0.44
NO
NO 4
NO
N:O
NO4
N:O
The Atom
History and Structure
Atomic Discovery and Structure
The Atom
Atom
An atom is the smallest particle of an element that
retains the chemical properties of that element
The nucleus is a very small region located at the center
of an atom
The nucleus is made up of at least one positively
charged particle called a proton and usually one or
more neutral particles called neutrons
The Atom
Atom
Surrounding the nucleus is a region occupied by
negatively charged particles called electrons
Protons, neutrons, and electrons are often referred to
as subatomic particles
The Atom
The Atom
• Discovery of the Electron
• Cathode Rays and Electrons
» Experiments in the late 1800s showed that cathode rays
were composed of negatively charged particles
» These particles were named electrons
The Atom
Joseph John Thomson’s (1987) cathode-ray tube experiments
measured the charge-to-mass ratio of an electron
The Atom
• Charge and Mass of the Electron
• Robert A. Millikan’s (1909) oil drop experiment
measured the charge of an electron
• With this information, scientists were able to determine
the mass of an electron
Atomic Discoveries: Experiments
• file:///D:/student/ch03/sec02/vc02/hc603_02
_v02fs.htm
Discovery of the Atomic Nucleus
• More detail of the atom’s structure was provided in
1911 by Ernest Rutherford and his associates
• The results of their gold foil experiment led to the
discovery of a very densely packed bundle of matter
with a positive electric charge
• Rutherford called this positive bundle of matter the
nucleus
Atomic Discoveries: Experiments
• file:///D:/student/ch03/sec02/vc02/hc603_02
_v02fs.htm
The Atom
• Composition of the Atomic Nucleus
• All atomic nuclei are made of protons and neutrons
• A proton has a positive charge equal in magnitude to
the negative charge of an electron
• Atoms are electrically neutral because they contain
equal numbers of protons and electrons
• A neutron is electrically neutral
Composition of the Atomic Nucleus
• The nuclei of atoms of different elements differ in their
number of protons and therefore in the amount of
positive charge they possess
• Thus, the number of protons determines that atom’s
identity
Size of the Atom
The radius of an atom is the distance from the center of
the nucleus to the outer portion of its electron cloud
Because atomic radii are so small, they are expressed
using a unit that is more convenient for the sizes of
atoms
This unit is the picometer, pm (10 -12)
Atomic Timeline
• With your table, you are to create an Atomic
Discovery Timeline/Historical Collage that
•Each person or
includes the following:
•
•
•
•
•
•
•
•
•
Democritus
Aristotle
Law of Conservation of Mass
Law of Definite Proportions
Law of Multiple Proportions
John Dalton
Joseph Thompson
Robert Millikan
Ernest Rutherford
discovery should be on
one piece of paper and
include a summary,
date, and illustration