atomic

1. By: Group 2

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. A r istotle
•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
• Wate
r
Fir
e
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

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,

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.

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

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..!!