Transcript A Pictorial History of Atomic Theory

A Pictorial History of Atomic
Theory
From Ancient Greece to Modern
Quantum Physics
Democritus 460-370 BCE
• Democritus was a
Greek philosopher
and not an
experimental scientist.
• He thought that there
would be a particle
that would be
indivisible.
Ancient Greek Model
• He called this particle
“atomos” or
uncuttable.
• It is not a detailed or
useful model.
• He thought some were
smooth and some
were sharp.
John Dalton 1766-1844
• Dalton was a British
experimental scientist.
• Dalton’s model of an
atom was not that
much advanced from
the ideas of
Democritus.
• He contributed
important ideas about
atoms.
Solid Sphere Model
• Atoms cannot be
broken into smaller
pieces.
• In any element, all the
atoms are exactly
alike.
• Atoms of 2 or more
elements can combine
to form compounds.
Solid Sphere Model
• Atoms of each
element have a unique
mass.
• The masses of the
elements in a
compound are always
in a constant ratio.
J.J. Thomson 1856-1940
• Thomson
experimented with
with particles and
found that they did
not behave as
predicted by Dalton’s
idea of an atom.
• He discovered the
existence of the
electron.
Plum Pudding Model 1900
• An atom that was
composed of a
positively charged
sphere and negatively
charged particles fit
his observations.
Hantaro Nagaoka 1865-1950
• Hantaro Nagaoka was
a Japanese physicist.
He was educated in
Japan and Europe. He
taught at the
University of Tokyo.
Saturnian Model 1904
• He proposed an atom
with a large positively
charged nucleus and
negatively charged
particles orbiting it.
• His idea was like
Saturn with a huge
planet holding
orbiting rings.
Ernest Rutherford 1871-1937
• Rutherford thought
that the atom was
mostly empty space –
not a huge nucleus.
Planetary Model 1911
• Rutherford still
pictured orbiting
electrons but
randomly in all
dimensions around a
smaller nucleus.
Niels Bohr 1885-1962
• Bohr was a Danish
physicist.
• He found that these
models did not
explain what he was
observing.
• They did not explain
how energy was
absorbed or released
in chemical reactions.
Planetary with Energy Shells
1913
• He proposed that
electrons moved from
one energy shell to
another rather than
randomly and that this
explained how the
energy is absorbed or
released.
Planetary with Energy Shells
1913
• He also proposed that
the chemical
properties of an
element are
determined by the
electrons in the
outermost orbit.
Many Scientists
• Contributions of
many scientists have
made advancements
in our concept of the
atom.
Electron Cloud Model
• We do not think in
terms of an orbital
path anymore but in
orbital regions where
there is a probability
of the electron being.
Sir James Chadwick 1891-1974
• Chadwick discovered
a missing piece of the
puzzle in the structure
of the atom.
• The weight of the
protons and electrons
did not add up to the
total weight of the
atom.
Neutrons in Nucleus
• Chadwick discovered
that there was another
particle in the nucleus
(as massive as the
proton but without
any charge).
• There are usually an
equal number of
protons and neutrons.
Neutrons in Nucleus
• Sometimes there are
different numbers of
neutrons than protons.
This changes the
atomic mass of the
atom. We call these
isotopes.
Modern Model of Atom
• Our current
understanding is of a
complicated atomic
structure.
• There are many sub
atomic particles and
forces.
• Electrons travel in
orbitals.