Atomic Theory

Let’s Take a Trip Through Time!

Democritus 400 B.C. There are various basic elements from which all matter is made Everything is composed of small atoms Some atoms are round, pointy, oily, have hooks, etc. to account for their properties

Democritus’s Model

John Dalton Introduced his ideas in 1803 Each element is composed of extremely small particles called atoms All the atoms of a given element are identical, but they differ from those of any other element Atoms are neither created nor destroyed in any chemical reaction

Dalton’s Model

J.J. Thompson 1904 Discovered electron (negative particle) in the Cathode Ray Experiment Plum Pudding model 1904 Electrons in a soup of protons (positive charges) There is an equal number of positive and negative charges because the atom is neutral

Cathode Ray Tube Experiment

Thompson’s Model Protons Electrons

Ernest Rutherford 1910 Nucleus Theory 1910 alpha particle gold foil experiment An atom’s mass is mostly in the nucleus The nucleus has a positive charge because it contains the protons and because it is so large in mass it contains another particle called the neutrons(neutral) Electrons in fixed orbit

Alpha Particle Experiment

Rutherford Model

Niels Bohr 1913 Planetary Model 1913 Nucleus surrounded by orbiting electrons at different energy levels Electrons have definite orbits Worked on the Manhattan Project (US atomic bomb)

Bohr’s Model Neutrons (No charge) Electrons (negative charge) Protons (positive charge)

Ernst Schrödinger Werner Heisenberg Quantum Mechanical Model 1926 Electrons are in probability zones called “orbitals”, not orbits and the location cannot be pinpointed and they are constantly moving (they are not moving in circular orbits) Schrödinger and Heisenburg’s Model of the Atom is the Model still accepted today.

Schrödinger and Heisenburg’s Model of the Atom