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”.

1. Atoms:Atoms:
Development ofDevelopment of
the Atomicthe Atomic
TheoryTheory

2. DemocritusDemocritus
 460 BC - Greek philosopher proposes460 BC - Greek philosopher proposes
the existence of thethe existence of the atomatom
 He pounded materials until he madeHe pounded materials until he made
them into smaller and smaller partsthem into smaller and smaller parts
 He called themHe called them atomaatoma which is Greekwhich is Greek
for “indivisible”.for “indivisible”.

3. DemocritusDemocritus
His Theory:His Theory:
All atoms:All atoms:
 Are small hard particlesAre small hard particles
 Are made of a single material formed intoAre made of a single material formed into
different shapes and sizesdifferent shapes and sizes
 Are always moving, and they formAre always moving, and they form
different materials by joining togetherdifferent materials by joining together

4. John DaltonJohn Dalton
 1803 - British chemist; elements1803 - British chemist; elements
combine in specific proportions to formcombine in specific proportions to form
compoundscompounds
Solid Sphere Model or
Bowling Ball Model
Proposed by John Dalton

6. John DaltonJohn Dalton
 His Theory:His Theory:
 All substances are made of atoms thatAll substances are made of atoms that
cannot be created, divided, or destroyed.cannot be created, divided, or destroyed.
 Atoms join with other atoms to make newAtoms join with other atoms to make new
substances.substances.
 Atoms of the same element are exactlyAtoms of the same element are exactly
alike, and atoms of different elements arealike, and atoms of different elements are
different in mass and size.different in mass and size.

7. J.J. ThomsonJ.J. Thomson
 1897 - English chemist and physicist;1897 - English chemist and physicist;
discovered 1discovered 1stst
subatomic particlessubatomic particles
Plum Pudding Model or
Raisin Bun Model
Proposed by J.J. Thomson

9. J.J. ThomsonJ.J. Thomson
His Theory:His Theory:
 Atoms contain negatively chargedAtoms contain negatively charged
particles calledparticles called electronselectrons andand positivelypositively
charged matter.charged matter.
 Created a model to describe the atom as aCreated a model to describe the atom as a
sphere filled with positive matter withsphere filled with positive matter with
negative particles mixed innegative particles mixed in
 Referred to it as the plum pudding modelReferred to it as the plum pudding model

10. Ernest RutherfordErnest Rutherford
 1912 - New Zealand physicist1912 - New Zealand physicist
discovered the nucleusdiscovered the nucleus
Nuclear Model
Proposed by Ernest
Rutherford

11. Ernest RutherfordErnest Rutherford
His Theory:His Theory:
 Small, dense, positively charged particleSmall, dense, positively charged particle
present inpresent in nucleusnucleus called acalled a protonproton
 ElectronsElectrons travel around thetravel around the nucleus,nucleus, butbut
their exact places cannot be described.their exact places cannot be described.

13. Niels BohrNiels Bohr
 1913 - Danish physicist; discovered1913 - Danish physicist; discovered
energy levelsenergy levels
Bohr Model or Planetary
Model
Proposed by Niels Bohr

14. Niels BohrNiels Bohr
His Theory:His Theory:
 ElectronsElectrons travel around the nucleus intravel around the nucleus in
definite paths and fixed distances.definite paths and fixed distances.
 Electrons can jump from one level to aElectrons can jump from one level to a
path in another level.path in another level.

15. Erwin ShrodingerErwin Shrodinger
 1924 - Austrian physicist; developed1924 - Austrian physicist; developed
thethe electron cloudelectron cloud modelmodel
Electron Cloud Model
Proposed by Erwin
Schrodinger

16. Erwin ShrodingerErwin Shrodinger
His Theory:His Theory:
 The exact path of electrons cannot beThe exact path of electrons cannot be
predicted.predicted.
 The region referred to as the electronThe region referred to as the electron
cloud, is an area where electrons cancloud, is an area where electrons can
likely be found.likely be found.

17. James ChadwickJames Chadwick
 1932 - English physicist; discovered1932 - English physicist; discovered
neutronsneutrons
 His Theory:His Theory:
 NeutronsNeutrons have no electrical charge.have no electrical charge.
 Neutrons have a mass nearly equal to theNeutrons have a mass nearly equal to the
mass of a proton.mass of a proton.
 Unit of measurement for subatomicUnit of measurement for subatomic
particles is the atomic mass unit (particles is the atomic mass unit (amuamu).).

18. Modern Theory of theModern Theory of the
AtomAtom
 AtomsAtoms are composed of three mainare composed of three main
subatomicsubatomic particlesparticles: the: the electronelectron,, protonproton, and, and
neutronneutron..
 Most of theMost of the massmass of the atom is concentratedof the atom is concentrated
in thein the nucleusnucleus of the atom.of the atom.

19. Modern Theory of theModern Theory of the
AtomAtom
 TheThe protonsprotons andand neutronsneutrons are locatedare located withinwithin
thethe nucleusnucleus, while the, while the electronselectrons existexist
outsideoutside of the nucleus.of the nucleus.
 In stable atoms, the number ofIn stable atoms, the number of protonsprotons isis
equalequal to the number ofto the number of electronselectrons..

20. Modern Theory of theModern Theory of the
AtomAtom
 The type of atom is determined by theThe type of atom is determined by the
number ofnumber of protonsprotons it has.it has.
 The number of protonsThe number of protons in an atom is equal toin an atom is equal to
thethe atomic numberatomic number..

21. Modern Theory of theModern Theory of the
AtomAtom
 The sum of the number of protonsThe sum of the number of protons andand
neutrons in a particular atom is called theneutrons in a particular atom is called the
atomicatomic massmass..
 Valence electronsValence electrons are the outermostare the outermost
electrons.electrons.