atomic theory

1. By: Group 2 (Cappuccino)

2. Democritus 460 BC
• Greek philosopher proposes the
existence of the atom.
• 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

3. Aristotle
• He did not think there
was a limit to the number
of times matter could be
divided.
• He thought that all substances were
built up from only four elements.
• Earth
• Water
Fire
Air

4. John Dalton 1766-1844
• British chemist
• 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.

5. Dalton’s Model
• Solid Sphere
Model or
Bowling Ball
Model
• Proposed by
John Dalton

6. J.J. Thomson
1856-1940
• English chemist and physicist;
discovered 1st subatomic particles.
• 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

7. J.J. Thomson’s Model
• Plum Pudding
Model or
Raisin Bun
Model
• Proposed by
J.J. Thomson

8. Ernest Rutherford
1871-1937
• New Zealand physicist
discovered the nucleus.
• 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.

9. Rutherford’s Model
•Nuclear
Model
•Proposed
by Ernest
Rutherford

10. Neils Bohr 1913
• Danish physicist; discovered
energy levels.
• 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.

11. Bohr’s Model
• In Bohr’s model,
electrons move with
constant speed in fixed
orbits around the
nucleus, like planets
around a sun.
• Bohr proposed that
electrons move in paths at
certain distances around
the nucleus.
• Electrons can jump from a
path on one level to a path
on another level.

12. Erwin Shrodinger
1924
• Austrian physicist; developed
the electron cloud model.
• 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.

13. Erwin Shrodinger’s Model
•Electron
Cloud Model
•Proposed by
Erwin
Schrodinger

14. James Chadwick 1932
• 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).

15. 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.
• 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.

16. • 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.
• The sum of the number of protons and
neutrons in a particular atom is called the
atomic mass.
• Valence electrons are the outermost
electrons.

17. Thank
you..!!