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Atomic History Timeline. Major Contributors Main Discoveries. Objectives. 4.1.1) List the main points of Dalton’s Atomic Theory and describe which parts are still believed to be true 4.1.2) Explain the atomic models of the following scientists: Dalton, Thomson, Rutherford, Bohr, Schrödinger

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Atomic History Timeline

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Atomic history timeline

Atomic History Timeline

Major Contributors

Main Discoveries



  • 4.1.1) List the main points of Dalton’s Atomic Theory and describe which parts are still believed to be true

  • 4.1.2) Explain the atomic models of the following scientists: Dalton, Thomson, Rutherford, Bohr, Schrödinger

  • 4.1.3) Describe the experiments performed by Thomson and Rutherford and what the observations suggested about the structure of the atom

  • Explain the contributions of the following scientists to the development of the Atomic Theory: Democritus, Crookes, Becquerel, Curie, Millikan, Chadwick

Democritus s theory foundation of atomic theory

Democritus’s Theory(Foundation of Atomic Theory)

  • Thought that all things were made of tiny, invisible, indestructible particles, called atoms

  • Thought atoms varied in size, shape and weight

Aristotle s theory

Aristotle's Theory

  • Opposed the Atomic Theory

  • Thought matter was made of air, water, fire, and Earth

Dalton s atomic theory

Dalton’s Atomic Theory

  • Chemical elements are made of atoms

  • Atoms are indestructible (can’t be divided into smaller parts)

  • Atoms have no electric charge

  • Each atom of the same element is identical

  • When elements react, their atoms combine in simple, whole-number ratios

Crooke s tube

Crooke’s Tube

Henri becquerel

Henri Becquerel

  • When Becquerel placed uranium salt in a desk drawer with a photographic plate, radiation from the uranium formed an image on the plate.

  • This proved that radiation could occur without outside energy such as the sun

  • When he placed metal between the uranium and photographic plates, the metal blocked the radiation

  • Discovered natural radiation

  • Discovered that a magnetic field could block radiation

Marie curie

Marie Curie

  • Confirmed the work of Becquerel

  • Invented the term “radioactivity”

  • Discovered two new elements: polonium and radium in 1898.

  • Her research indicated that some atoms are unstable and will disintegrate over time on their own.

    • If they fall apart, the must not be the smallest piece of matter out there

Jj thomson

JJ Thomson

  • Discovered electrons using the Cathode Ray Tube (CRT)

  • Beam will bend towards a positive charge, therefore, it must be made of negatively charged particles

Thomson s atomic model plum pudding model

Thomson’s Atomic Model“Plum Pudding” Model

  • He realized that neutral atoms must have equal amounts of positive and negative charge.

  • His model shows negative charges as plums and positive charges as the pudding.

Rutherford s gold foil experiment

Rutherford's Gold Foil Experiment

  • Consisted of shooting alpha particles (positive charge) at a very thin piece of gold.

  • Most went straight through, some deflected at an angle, and a small percentage bounced straight back

Rutherford s contribution to atomic theory

Rutherford’s Contribution to Atomic Theory

  • Atoms are mostly empty space.

  • Atoms have a tiny dense center called ‘the nucleus’.

  • Nucleus contains most of the mass of an atom.

  • Electrons are found outside of the nucleus.

  • Nucleus is positively charged.

Bohr s atomic model

Bohr’s Atomic Model

  • Electrons exist in orbits around the nucleus

  • Electrons can sometimes jump from one orbit to another by gaining or releasing energy

Robert millikan

Robert Millikan

  • Discovered mass and electric charge of the electron by using the “Falling Drop” Method

Erwin schr dinger

Erwin Schrödinger

  • Stated that one could only predict the probability of where an electron could be (based on a mathematical formula), not its exact location

  • These probabilities form a region of space around the nucleus that he called orbitals (the most probable location of the electrons).

James chadwick

James Chadwick

  • Discovered the neutron in 1932

  • Neutrons have approximately the same mass as protons

  • Neutrons have no electric charge

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