Transcript Powerpoint for Scientist Contributions and the Modern Theory of

Powerpoint for Scientist
Contributions and the Modern
Theory of Atoms
Mrs. Rigby
Science 8
What is the smallest unit of matter?
Can we see atoms?
So, how do we know about them?
Powers of 10
At what point can you no longer see the objects with your eyes?
What tools would help magnify things?
Size of an atom: 0.00000002 cm or 2 hundred millionth of a cm
Excuse me, how can you discover a particle
so small that nobody has ever seen one?
Democritus
Greek Philosopher
400 B C
Atomos
Democritus
• 460 BC - Greek philosopher proposes the
existence of the atom
• He pounded materials until he made them
into smaller and smaller parts
• He called them atoma which is Greek for
“indivisible”.
Democritus
• His Theory:
All atoms:
– Are small hard particles
– Are made of a single material formed into
different shapes and sizes
– Are always moving, and they form different
materials by joining together
John Dalton
• 1803 - British chemist; elements combine in
specific proportions to form compounds
Solid Sphere Model
John Dalton
• His Theory:
 All substances are made of atoms that cannot be
created, divided, or destroyed.
 Atoms join with other atoms to make new
substances.
 Atoms of the same element are exactly alike, and
atoms of different elements are different in mass
and size.
Edward Frankland
• 1852 - English chemist; developed the valence
theory
• His theory:
– Every atom has a fixed number of bonds that it
can form
– For the atom to be stable, all of these bonds must
be used
J.J. Thomson
• 1897 - English chemist and physicist;
discovered 1st subatomic particles
Plum Pudding Model or
Raisin Bun Model
Proposed by J.J. Thomson
J.J. Thomson
• His Theory:
– Atoms contain negatively charged particles called
electrons and positively charged matter.
– Created a model to describe the atom as a sphere
filled with positive matter with negative particles
mixed in
– Referred to it as the plum pudding model
Ernest Rutherford
• 1912 - New Zealand physicist discovered the
nucleus
Nuclear Model
Proposed by Ernest
Rutherford
Ernest Rutherford
• His Theory:
 Small, dense, positively charged particle present in
nucleus called a proton
 Electrons travel around the nucleus, but their
exact places cannot be described.
Niels Bohr
• 1913 - Danish physicist; discovered energy
levels
Bohr Model or Planetary
Model
Proposed by Niels Bohr
Niels Bohr
• His Theory:
 Electrons travel around the nucleus in definite
paths and fixed distances.
 Electrons can jump from one level to a path in
another level.
Erwin Shrodinger
• 1912 - Austrian physicist; developed the
electron cloud model
Electron Cloud Model
Proposed by Erwin
Schrodinger
Erwin Shrodinger
• His Theory:
 The exact path of electrons cannot be predicted.
 The region referred to as the electron cloud, is an
area where electrons can likely be found.
James Chadwick
• 1924 - English physicist; discovered neutrons
• His Theory:
 Neutrons have no electrical charge.
 Neutrons have a mass nearly equal to the mass of
a proton.
 Unit of measurement for subatomic particles is
the atomic mass unit (amu).
Modern Theory of the Atom
• Atoms are composed of three main subatomic
particles: the electron, proton, and neutron.
• Most of the mass of the atom is concentrated in the
nucleus of the atom.
Modern Theory of the Atom
• The protons and neutrons are located within the
nucleus, while the electrons exist outside of the
nucleus.
• In stable atoms, the number of protons is equal to
the number of electrons.
Modern Theory of the Atom
• The type of atom is determined by the number of
protons it has.
• The number of protons in an atom is equal to the
atomic number.
Modern Theory of the Atom
• The sum of the number of protons and neutrons in a
particular atom is called the atomic mass.
• Valence electrons are the outermost electrons.