Part II. 1897 - Discovers the Electron Experimented with cathode rays Took a glass tube and pumped most of the air out of it. Applied a high voltage that.

Part II

History of the Atom

1897 - Discovers the ElectronExperimented with cathode raysTook a glass tube and pumped

most of the air out of it. Applied a high voltage that

traveled from the negative cathode to the positive anode.

The radiation that was produced from this high voltage is known as a cathode ray.

Joseph John Thomson

In his first experiment he deflected the cathode ray by introducing a magnetic field.

In his second experiment he deflected the cathode ray by introducing an electric field.

From these experiments he determined that the particles in the cathode ray were negatively charged particles emitted by atoms called electrons.

Thomson continued

Thomson ContinuedThomson concluded that

the atom was a positively charged mass that was filled with these tiny negatively charged electrons.

This model of the atom is referred to as the plum pudding model.

Robert Millikan1909 - calculated the charge of an electronSmall droplets of oil were

dropped between electrically charged plates.

Millikan was able to determine the charge by varying the voltage of the plates and observing how it effected the rate of falling.

Determine the charge to be 1.602 x 10-19 Coulomb.

1910 – Credited with the discovery of the protonWorked on his gold foil

experiment with Geiger and Marsden.

Noticed that when alpha particles were aimed at a piece of gold foil, most of them passed through but with a small amount deflected back.

Ernest Rutherford

Rutherford’s gold foil experiment provided data that was inconsistent with Thomson’s cathode ray experiment.

Rutherford explained his results by stating that the atom had an extremely dense region called the nucleus. He stated that most of the atom was empty space in which the electrons orbited this nucleus.

Rutherford continued

1913 - Established that the electrons were spinning in orbitsRefined Rutherford’s idea

of electrons rotating around a dense nucleus.

Determined that the orbits could only contain a set number of electrons

Niels Bohr

Used Planck’s constant, developed by Max Planck to determine that electrons were orbiting at different energy levels.

Electrons can gain or lose energy by jumping from different energy levels

h is Planck’s constant.

Bohr Continued

1926 - Schrödinger developed the Quantum Mechanical Model of the Atom. Looking at Bohr’s model, he used

mathematical equations to determine the likelihood of finding an electron in a certain position.

In this view of the atom, electrons are orbiting the nucleus in different energy level, orbitals with varying spatial arrangements.

Erwin Schrödinger

Quantum Mechanical Model

1932 – Discovered the neutronSmashed alpha particles

into BerylliumThe radiation that was

released hit hydrogen atoms in paraffin wax and sent them to a detecting chamber. (This could only happen if the particles that were released from radiation were the same size as a hydrogen atom. )

James Chadwick

Chadwick continued