Download The history of the atomic model

THE HISTORY OF
THE ATOMIC MODEL
DEMOCRITUS
4 6 0 B. C. T O 3 7 0 B. C.
All matter consists of
extremely small particles that
cannot be divided.
Called them “Atoms”
from Greek atomos meaning
indivisible
ARISTOTLE
384 BC – 320 BC
There is no limit to
how many times you can
divide matter.
Aristotle:
Four elements:
Earth
Water
Air
Fire
For many centuries,
people believed
Aristotle’s theory of
matter
John Dalton
1766-1844
Dalton’s Theory:
1) All elements are composed of atoms
2) All atoms of the same element have the same
mass, and atoms of different elements have
different masses
3) Compounds contain atoms of more than one
element
4) In a particular compound, atoms of different
elements always combine in the same
proportions
Dalton made these wooden spheres to
represent the atoms of different elements
Dalton’s model of the atom is sometimes called
the “solid sphere” or “Billiard ball” model
Joseph John (J.J.) Thomson
1856-1940
Cathode Ray Tube
• Thomson calculated the mass and
charge of the particles in the beam
• Negatively charged, 2000 times
smaller than a hydrogen atom
• Concluded that atoms must contain
tiny, negatively-charge particles
• Thomson had discovered the first
subatomic particle, the electron
Thomson’s “Plum
Pudding” model
Small electrons
moving around in
a sea of positive
charge
Ernest Rutherford
1871-1937
Designed an experiment in
which small, positively
charged particles were
launched at a thin sheet of
gold
The experiment was performed by his
students Geiger and Marsden
He expected the particles to fly straight through
Rutherford concluded that all of the
positive charge and nearly all the mass
of an atom was located in a tiny
nucleus in the center.
Electrons orbit around the nucleus
like planets around the sun
Rutherford’s
model of the
atom
Neils Bohr
1885-1962
Proposed a theory that
electrons can only be
stable at certain distances
from the nucleus
The electrons in orbits
farther from the nucleus
have more energy
Bohr Model
of the atom
Erwin Schrödinger
Werner Heisenberg
1925
Schrodinger and Heisenberg:
The Electron Cloud
James Chadwick
In 1932, discovered the
neutron
Neutrons are found in
the nucleus
They are about the same
size as protons
They have zero charge
The History of the Atomic model
Atoms are made up of
protons, neutrons, and
electrons.
Protons have a positive
charged, and neutrons have no
charge.
Protons and neutrons make up
the nucleus in the center of the
atom.
Electrons have a negative charge and
orbit the nucleus.
The nucleus contains nearly all the
atom’s mass. Protons and neutrons
both have around 1800 times more
mass than electrons.
Electrons are located in the electron
cloud, an area that surrounds and is
much larger than the nucleus.