1800

1803 - J. Dalton: defined atom as the smallest part of a subs. that can participate in a chem. rxn.

1835 - C. Wheatstone: different metals ,different bright lines in their sparks’ emission spectra

1850

1853 - Angstrom

1860 – Kirchoff:

showed that there are three types of spectra emitted by objects

1869 - Mendeleev: published the periodic table

1900

1900 – Planck: thermal radiation is emitted from

a heated surface in discrete packets of energy called QUANTA. Quantum theory is born.

1904 - J.J. Thomson: Plum–Pudding Model: the atoms of the elements consist of a number of negatively electrified corpuscles enclosed in a sphere of uniform positive electrification...

1905 – Einsteininterpreted the photoelectric results by suggesting that

the energy in a ight wave is also contained in discrete packets.

The particle-like packet of energy is called a PHOTON.

1911 – E. Rutherford proposes the nuclear atomic model.

1913 - N. Bohr proposes his planetary model of the atom, along with the concept of stationary energy states and accounts for hydrogen spectrum.

1924 - De Broglie generalizes wave-particle duality by suggesting that particles of matter are also wavelike.

1924 -Bose & Einstein find a new way to count quantum particles (Bose-Einstein statistics), and they predict that extremely cold atoms should condense into a single quantum state, later known as a Bose-Einstein condensate.

1925 – Pauli enunciates the exclusion principle.

1926 - Schrödinger develops a second description of quantum physics, called wave mechanics to describe the motion of electrons in a crystal.

Under construction

1926 – Fermi and Dirac find that quantum mechanics requires a second way to count particles, Fermi-Dirac statistics, opening the way to SOLID STATE PHYSICS.

1927 - Heisenberg states his UNCERTAINTY PRINCIPLE, that it is impossible to exactly measure the position and momentum of a particle at the same time.

1950