Download HISTORY OF THE ATOM AND ATOMIC THEORY

HISTORY OF THE ATOM
AND
ATOMIC THEORY
ATOMS
• The smallest part of an
element that retains the
properties of that element
DEMOCRITUS
• Greek philosopher
• Came up with the word
“atom”
• Thought atoms were
indivisible (couldn’t be
broken down any further)
JOHN DALTON
• All atoms of an element are exactly
alike.
• Atoms of different elements
combine to form compounds.
• Law of Definite Proportions - those
compounds always contain elements
in the exact same proportions
–Ex.; water is always H2O
JJ Thomson
• Discovered atoms were NOT indivisible…
they could be divided into smaller parts
• Discovered electrons – negatively charged
particles within the atom
• Plum-Pudding Model – said the electrons
were spread throughout the atom
ERNEST RUTHERFORD
• Gold foil experiment – helped revise
Thomson’s Plum-Pudding model
– positively charged particles aimed at a thin sheet
of gold foil.
– thought most particles would travel straight
through the foil, a few would be slightly
deflected.
– most went through, but some were deflected by
a large amount
– this indicated there was a positive charge in the
center of the atom, and the center was small
compared to the size of the atom
GOLD-FOIL EXPERIMENT
RUTHERFORD’S MODEL OF THE
ATOM
• Nucleus – center of the atom containing
protons (positively charged) and neutrons
(no charge)
• Electrons – negatively charged particles
that orbit around the nucleus
NIELS BOHR
• Suggested electrons are in certain
energy levels surrounding the nucleus
and they gain energy to move to higher
levels or lose energy to move to lower
levels
MODERN ATOMIC THEORY
• Nucleus of an atom is small, dense & in
the center with protons and neutrons.
• Electrons don’t occupy energy levels
• Electrons behave more like waves than
particles
• It’s impossible to pinpoint the exact
location of an electron
• Orbital – region of space around the
nucleus where an electron is likely to be