Atomic History Timeline

1
Atomic History Timeline

• Major Contributors
• Main Discoveries

2
Objectives

• 4.1.1) List the main points of Daltons 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

3
Democrituss 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

4
Aristotle's Theory

• Opposed the Atomic Theory
• Thought matter was made of air, water, fire, and
  Earth

5
Daltons Atomic Theory

• Chemical elements are made of atoms
• Atoms are indestructible (cant 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

6
Crookes Tube
7
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

8
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

9
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

10
Thomsons Atomic ModelPlum 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.

11
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

12
Rutherfords 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.

13
Bohrs Atomic Model

• Electrons exist in orbits around the nucleus
• Electrons can sometimes jump from one orbit to
  another by gaining or releasing energy

14
Robert Millikan

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

15
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).

16
James Chadwick

• Discovered the neutron in 1932
• Neutrons have approximately the same mass as
  protons
• Neutrons have no electric charge