Download Atom Democritus Dalton Thompson Rutherford Bohr Electron Cloud

Science 7
Notes 12
Atom
Democritus
Dalton
Thompson
Rutherford
Bohr
Electron Cloud Model
How has the
model of the atom
changed over
time?
HISTORY – The modern model of the atom has evolved over long
periods of time through the work of many scientists
Who proposed
the atom?
Earliest Model - 4th Century B.C.
• Democritus, a famous Greek teacher proposed the idea of the atom.
What is an atom?
• Democritus said that all matter was made of tiny,
indivisible particles
• Called these particles atoms.
Atom = Solid
Sphere
An atom is the smallest unit that retains chemical identity
of that element.
What 4 pieces of
information did
Dalton write
about atoms?
Dalton’s Model – 1800’s
• John Dalton came up with his atomic theory based on the results of
his experiments.
In what ways did
• Dalton published a paper about atoms which stated
Dalton and
Democritus
1. Atoms are indivisible and indestructible
agree?
2. Atoms of the same element are exactly alike
3. Compounds are formed by combining atoms
4. Chemical reactions are rearrangements of atoms
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Science 7
Notes 12
The Atomic Structure
What are the
• The smallest particle of an element is an atom.
subatomic
•
particles?
The atom is made up of three subatomic particles:
• Electrons, protons, and neutrons
Which subatomic
particles were 1st
identified?
Who discovered
electrons?
What was the
name of JJ
Thompson’s
atomic model?
What are the 2
parts of the atom?
Electrons:
Discovered in 1897 by J. J. Thomson.
• Developed the plum pudding model. This
said that negatively charged electrons
were stuck on a positively charged ball.
• The electron has a negative charge. Its mass is much
smaller than the other 2 subatomic particles, therefore its mass is
usually ignored.
Nuclear Model
We know today that the atom is made up of 2 parts/sections:
Where are they
(1) The Nucleus --- (in the center of the atom)
located?
(2) The Electron Cloud --- (surrounds the nucleus)
Who discovered
the proton?
The nucleus was Discovered by Ernest Rutherford in 1911.
• Rutherford’s gold foil experiment proved:
What experiment
(1) Most of the atom is more or less empty space
was used to
(2) The nucleus is very tiny (Stadium Analogy)
discover the
proton?
(3) The nucleus is very dense. (Large Mass ÷ Small Volume)
(4) The nucleus is positively charged.
How did
Rutherford
change the
atomic model?
Who told where
Rutherford had identified the proton.
1913 Niels Bohr first explained where the electrons go.
• According to his model, electrons are arranged like planets around the
sun in energy levels
the electrons go?
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Science 7
What is the
charge on a
neutron?
Notes 12
Neutrons
 Neutrons do not have a charge. In other words, they are neutral.
 The neutron was discovered in 1932. The neutron has about the
What subatomic
particle has the
same mass as a
neutron?
same mass as the proton. Neutrons keep the nucleus intact.
Modern Electron Cloud Model
• Electrons exist in orbitals (areas of probability of finding an electron)
What is the name
of the modern
atomic model?
In the modern
model, where are
electrons located?
Describe how the
model of the
atom has changed
over time.
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