atoms: development of the atomic theory. democritus 460 bc - greek philosopher proposes the...

Atoms:Atoms:Development of Development of

the Atomic the Atomic TheoryTheory

DemocritusDemocritus

460 BC - Greek philosopher proposes 460 BC - Greek philosopher 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 small hard particles Are small hard particles

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

Are always moving, and they form Are always moving, 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 substances are made of atoms that All 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 new Atoms join with other atoms to make new substances.substances.

Atoms of the same element are exactly Atoms of the same element are exactly alike, and atoms of different elements are alike, and atoms of different elements are different in mass and size.different in mass and size.

J.J. ThomsonJ.J. Thomson

1897 - English chemist and physicist; 1897 - English chemist and physicist; discovered 1discovered 1stst 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 negatively charged Atoms contain negatively charged

particles called particles called electrons electrons andand positively positively charged matter.charged matter.

Created a model to describe the atom as Created a model to describe the atom as a sphere filled with positive matter with a sphere 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

Ernest RutherfordErnest Rutherford

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

Nuclear ModelProposed by Ernest

Rutherford

Ernest RutherfordErnest Rutherford

His Theory:His Theory: Small, dense, positively charged particle Small, dense, positively charged particle

present in present in nucleusnucleus called a called a protonproton

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

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 and fixed distances.definite paths and fixed distances.

Electrons can jump from one level to a Electrons can jump 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

predicted.predicted.

The region referred to as the electron The region referred to as the electron cloud, is an area where electrons can cloud, 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 no electrical charge. have no electrical charge. Neutrons have a mass nearly equal to Neutrons have a mass nearly equal to

the mass of a proton.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).).

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.