Atomic Theory: the beginningAtomic Theory: the beginning

Chapter 3 Part IChapter 3 Part I

DemocritusDemocritusAn Ancient GreekAn Ancient Greek

Theorized about Theorized about the existence of the existence of atoms.atoms.

Did not use Did not use Scientific Method.Scientific Method.

John DaltonJohn DaltonA school teacher in A school teacher in England.England.

Worked out his Worked out his ideas at home.ideas at home.

Used Scientific Used Scientific Method.Method.

Dalton’s Atomic TheoryDalton’s Atomic TheoryAll Elements are composed of tiny All Elements are composed of tiny indivisible particles called atoms.indivisible particles called atoms.Atoms of the same element are Atoms of the same element are identical. Atoms of one element are identical. Atoms of one element are different from any other element.different from any other element.Atoms of different elements can Atoms of different elements can physically mix or chemically combine physically mix or chemically combine with one another in simple whole with one another in simple whole number ratios.number ratios.Chemical reactions occur when atoms Chemical reactions occur when atoms are separated, joined, or rearranged as are separated, joined, or rearranged as a result of a chemical reaction.a result of a chemical reaction.

Dalton’s Atomic TheoryDalton’s Atomic Theory

ElectronsElectronsAtoms are know to Atoms are know to be divisible.be divisible.

One part of the One part of the atom, the electrons atom, the electrons are negatively are negatively charged subatomic charged subatomic particles.particles.

These were These were discovered by JJ discovered by JJ Thomson.Thomson.

Possible video of Cathode TubesPossible video of Cathode Tubes

http://www.chem.uiuc.edu/clcwebsitehttp://www.chem.uiuc.edu/clcwebsite/cathode.html/cathode.html

FoxTrotFoxTrot

Millikan and the charge of an Millikan and the charge of an electronelectron

http://www.britannica.http://www.britannica.com/nobel/cap/omillikcom/nobel/cap/omillik001a4.html001a4.html

Robert Millikan carried Robert Millikan carried out experiments that out experiments that allowed him to allowed him to calculate the charge calculate the charge and mass of an and mass of an electron. Charge is electron. Charge is one unit and mass is one unit and mass is 1/1840 the mass of a 1/1840 the mass of a hydrogen atom.hydrogen atom.

ProtonsProtonsE. Goldstein observed a E. Goldstein observed a cathode-ray tube and cathode-ray tube and discovered rays discovered rays traveling in the traveling in the opposite direction.opposite direction.He called these canal He called these canal rays and That they had rays and That they had a positive charge.a positive charge.We now call them We now call them protons. Their mass is protons. Their mass is 1840 times and 1840 times and electronelectron

NeutronsNeutronsJames Chadwick James Chadwick confirms the confirms the existence of the existence of the neutron. These neutron. These have no charge but have no charge but add weight to the add weight to the atom.atom.

How did the modern atomic model How did the modern atomic model develop?develop?

http://www.mhhe.com/physsci/chemihttp://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther1stry/essentialchemistry/flash/ruther14.swf4.swf

Development of Atomic modelDevelopment of Atomic modelIt all started with It all started with Plum Pudding.Plum Pudding.

Not this Plum Not this Plum Pudding!!Pudding!!

This is JJ Thompson’s Plum This is JJ Thompson’s Plum Pudding ModelPudding Model

Rutherford’s ModelRutherford’s ModelRutherford realized Rutherford realized from his experiments from his experiments that the positively that the positively charged particles charged particles had converged into a had converged into a small “nucleus” in small “nucleus” in the center of the the center of the atom and were atom and were surrounded by the surrounded by the very small electrons.very small electrons.

Bohr’s modelBohr’s model

Bohr took Bohr took Rutherford’s Rutherford’s model one step model one step further and further and theorized the theorized the electrons orbit electrons orbit the nucleus.the nucleus.

Common View: But is it correct?Common View: But is it correct?