Atoms:Atoms:Development of Development of

the Atomic the Atomic TheoryTheory

S.MORRIS 2006

Who are these men?Who are these men?In this lesson, we’ll learn about the men whose quests for knowledge about the fundamental nature of the universe helped define our views.

DemocritusDemocritus

460 BC - Greek philosopher 460 BC - Greek philosopher proposes proposes the existence of the the existence of the atom atom

He pounded materials until he made He pounded materials until he made them into smaller and smaller partsthem into smaller and smaller parts

He called them He called them atoma atoma which is which is Greek for “indivisible”.Greek for “indivisible”.

DemocritusDemocritus

His Theory:His Theory:All atoms: All atoms: Are Are smallsmall hard particles hard particles

Are made of a Are made of a single material single material formed formed into different shapes and sizesinto different shapes and sizes

Are always Are always movingmoving, and they form , and they form different materials by joining togetherdifferent materials by joining together

John DaltonJohn Dalton

1803 - British chemist; elements 1803 - British chemist; elements combine in specific proportions to form combine in specific proportions to form compoundscompounds

Solid Sphere Model or Bowling Ball Model

Proposed by John Dalton

John DaltonJohn Dalton His Theory:His Theory:

All substancesAll substances are made of atoms that are made of atoms that cannot be created, divided, or destroyed.cannot be created, divided, or destroyed.

Atoms Atoms joinjoin with other atoms to make new with other atoms to make new substances.substances.

Atoms of the same element are Atoms of the same element are exactlyexactly alike, and alike, and

atoms of atoms of differentdifferent elements are elements are differentdifferent in mass and size.in mass and size.

J.J. ThomsonJ.J. Thomson

1897 - English chemist and physicist; 1897 - English chemist and physicist; discovered discovered 11stst subatomic particles subatomic particles

Plum Pudding Model or Raisin Bun Model

Proposed by J.J. Thomson

J.J. ThomsonJ.J. Thomson

His Theory:His Theory: Atoms contain Atoms contain negatively charged negatively charged

particles called particles called electronselectrons andand positively positively charged matter.charged matter.

Created a model to describe the atom as Created a model to describe the atom as a spherea sphere filled with positive matter with filled with positive matter with negative particles mixed innegative particles mixed in

Referred to it as the Referred to it as the plum pudding modelplum pudding model

Ernest RutherfordErnest Rutherford

1912 - New Zealand physicist 1912 - New Zealand physicist discovered the nucleusdiscovered the nucleus

Nuclear ModelProposed by Ernest

Rutherford

Ernest RutherfordErnest RutherfordHis Theory:His Theory:

Small, dense, positively charged Small, dense, positively charged particle present in particle present in nucleusnucleus called a called a protonproton

ElectronsElectrons travel around travel around the the nucleus,nucleus, but their exact places cannot be but their exact places cannot be described.described.

gold foil

helium nuclei

gold foil

helium nuclei

Niels BohrNiels Bohr 1913 - Danish physicist; discovered 1913 - Danish physicist; discovered

energy levelsenergy levels

Bohr Model or Planetary Model

Proposed by Niels Bohr

Niels BohrNiels Bohr

His Theory:His Theory: ElectronsElectrons travel around the nucleus in travel around the nucleus in

definite paths definite paths and fixed distances.and fixed distances.

Electrons can jump Electrons can jump from one level to a from one level to a path in another level.path in another level.

Erwin ShrodingerErwin Shrodinger

1924 - Austrian physicist; developed 1924 - Austrian physicist; developed the the electron cloud electron cloud modelmodel

Electron Cloud Model

Proposed by Erwin Schrodinger

Erwin ShrodingerErwin Shrodinger

His Theory:His Theory: The exact path of electrons cannot be The exact path of electrons cannot be

predictedpredicted..

The region referred to as the The region referred to as the electron electron cloudcloud, is an area where electrons can , is an area where electrons can likely be found. likely be found.

James ChadwickJames Chadwick 1932 - English physicist; discovered 1932 - English physicist; discovered

neutronsneutrons

His Theory:His Theory: NeutronsNeutrons have have no electrical chargeno electrical charge.. Neutrons have a mass Neutrons have a mass nearly equal nearly equal

to the mass of a protonto the mass of a proton.. Unit of measurement for subatomic Unit of measurement for subatomic

particles is the atomic mass unit particles is the atomic mass unit ((amuamu).).

The Atom’s Family The Atom’s Family Album!Album!

Levels of OrganizationLevels of OrganizationParts of MatterParts of Matter

largestsmallest

Atoms Family Album CoverAtoms Family Album Cover

Now if you a real ‘G’, as in GENIUS…… Now if you a real ‘G’, as in GENIUS…… What you know about this??? Which What you know about this??? Which

element is it?element is it?

Modern Theory of the Modern Theory of the AtomAtom

AtomsAtoms are composed of three main are composed of three main subatomicsubatomic particlesparticles: the : the electronelectron, , protonproton, , and and neutronneutron. .

Most of the Most of the massmass of the atom is of the atom is concentrated in the concentrated in the nucleusnucleus of the atom. of the atom.

Modern Theory of the Modern Theory of the AtomAtom

The The protons protons and and neutrons neutrons are located are located withinwithin the the nucleusnucleus, while the , while the electronselectrons exist exist outsideoutside of the nucleus. of the nucleus.

In stable atoms, the number of In stable atoms, the number of protonsprotons is is equalequal to the number of to the number of electronselectrons. .

Modern Theory of the Modern Theory of the AtomAtom

The type of atom is determined by the The type of atom is determined by the number of number of protons protons it has. it has.

The number of protonsThe number of protons in an atom is equal in an atom is equal to the to the atomic numberatomic number..

Modern Theory of the Modern Theory of the AtomAtom

The sum of the number of protonsThe sum of the number of protons and and neutrons in a particular atom is called the neutrons in a particular atom is called the atomicatomic massmass..

Valence electrons Valence electrons are the outermost are the outermost electrons.electrons.