Download Chapter 7 History of the Atomic Theory

History of the
Atomic Theory
Democritus and Aristotle
• Ancient Greek philosophers
that pronounced that the
atom was the smallest unit
of an element and it was
indivisible
Dalton
John Dalton
developed his
atomic theory
from observations
gathered from
many
experiments.
http://www.britannica.com/eb/art/print?id=15469&articleTypeId=0
Dalton’s Atomic Theory
•All substances are made
of atoms. Atoms are
small particles that
cannot be created,
divided, or destroyed.
Dalton’s Atomic Theory
•
Atoms of the same
element are exactly
alike, and atoms of
different elements are
different
Dalton’s Atomic Theory
•
Atoms join with other
atoms to make new
substances.
Dalton’s Atomic Image
J.J.
Thomson
o In 1897, J.J. Thomson made a
discovery that identified an error in
Dalton’s theory.
o There are small
particles inside
the atom.
Thomson’s Results
o Thomson discovered atoms can be
divided into even smaller parts.
o What he discovered was the “electron.”
Thomson called it a “corpuscle” back then.
J.J. Thomson
His atomic theory said that the
atom was a central sphere of
positive charge and was off set
by negative charges attached to
the outside of the atom.
Basically a “plum pudding”
structure
Revision of the Atomic
Theory
Because Thomson knew atoms have
no overall charge, he realized that
positive charges must be present to
balance the negative charges of the
electron.
Rutherford
(1909)
Ernest Rutherford,
a former student of
Thomson, designed an
experiment to investigate
the structure of the atom.
http://www.pbs.org/wgbh/aso/databank/entries/bpruth.html
Rutherford’s Model
Rutherford
Theorized that the atom was
made of a dense nucleus with
a positive charge and negative
charged particles circling the
nucleus in a “planetary type
orbit.”
Rutherford’s Atomic Image
Bohr (1913)
Neils Bohr was a Danish
scientist who worked
with Rutherford.
He suggested electrons
travel around the
nucleus in definite
paths.
http://www.pbs.org/wgbh/aso/databank/entries/bpbohr.html
These paths are located in energy
levels at certain distances away
from the nucleus.
Bohr’s Atomic Model
electron
neutron
proton
Chadwick (1932)
James Chadwick, an English
scientist, discovered the
“NEUTRON.”
He won the Nobel Prize for Physics in 1935, and
his research prepared the way for the
development of the atomic bomb.
http://nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html
Chadwick’s Atomic Image
Electrons do not travel in definite
paths around the nucleus like Bohr
thought.
This discovery was made by
scientist Erwin Schrodinger; it is
called an Electron Cloud
Erwin Schrodinger
Still more changes…
Many 20th century scientists have contributed to
our current understanding of the atom.
http://particleadventure.org/frameless/modern_atom.html
In the modern atomic theory…
The exact path of a moving electron cannot be
predicted, but there are regions inside the
atom where electrons are likely to be found.
These regions are called electron clouds.
https://www.youtube.com/watch?v=07yDiELe83Y
Atom Smasher in Switzerland
• A 17 mile diameter atom smasher
was built in Switzerland and
many scientist were worried that
when it went into operation there
might be particles found that
possibly might destroy mankind.
Picture of atom Smasher
ATOM
An atom is the smallest
particle into which an
element can be divided and
still be the same substance.
Atoms
• Atoms are basic
building blocks
of matter that
make up
everyday
objects.
Atoms
• Atoms have three
parts.
• They are Protons,
Neutrons, and
Electrons.
Electrons
• Electrons orbit around an
atom. In this picture, they
are the small yellow bits.
• They have a negative charge.
• They are lighter than protons
or neutrons.
• The number of
protons=number of
electrons in a neutral atom
Protons
• They are positively
charged.
• Are located in the nucleus.
• Atomic Number=Number
of protons
• In this picture, the protons
are the blue pieces in the
center of the atom.
Neutrons
• Neutrons are neither
positive nor negative.
• Neutrons are in the
nucleus of an atom.
• The atomic mass –
number of protons =
number of neutrons
• In this picture, neutrons
are the purple pieces in
the center of the atom.
Atomic Number
•The atomic number
is the number of
protons or electrons
in a neutral atom
8 is the atomic number of Oxygen
=the number of protons
11 is the atomic number of
Sodium= the number of protons
Atomic Mass
•Atomic mass is the
number of protons
and neutrons in a
neutral atom.
Number of protons and neutrons
is the atomic mass number
Number of protons and neutrons is
the atomic mass number
Chemical Symbol
•The chemical symbol is
either a capitalized single
letter or a capitalized
letter followed by a lower
case letter.
Capitalized Symbol if only
one letter
Capitalized first letter and
lower case second letter if
two letters
Element Name
•The name of the
element is usually
written below the
chemical symbol.