History of Chemistry

Leuccippus and Democritus

• proposed that matter is composed of tiny particles

• “atomos” = uncuttable or indivisible

• attributed properties of substances to the forms of the atom

Antoine Laboisier

• proposed the Law of Conservation of Mass

John Dalton

• all matter is made up of atoms

• atoms cannot be created or destroyed

• atoms are indivisible

• atoms combine to form compounds

• atoms of one element are different from atoms of another element

J.J. Thompson

• cathode raty tubes, discovered electrons

  • noticed that the ray bends toward positive charge and deflect negative charge

  • discovered that mass of rays were 1000 times lighter than a hydrogen

  • concluded cathode rays were very light, small negativel charged particles

  • “corpuscles” - electron

• developed the raisin bun or plum pudding model

Hantaro Nagaoka

• developed a Saturnian model

Ernest Rutherford

• gold foil experiment, determined atoms are mostly empty space

  • most alpha particles went through gold foil = mostly empty space

  • some alpha particles bounced back = very small, dense centre = nucleus

  • some alpha particles were deflected at large angles = alpha particles deflected by positive charge = proton

• discovered the nucleus to be very small and positively charged

• discovered if he bombarded nitrogen particles with alpha particles, it creates hydrogen ions = protons

Neils Bohr

• developed “shell” model of the atom, electrons travel on specific orbits around the nucleus

Dimitri Mendeleev

• organized 63 elements in periodic table,

• left gaps and predicted properties of undiscovered elements

Max Planck + Alber Winstein + Neils Bohr

• Quantum theory = electrons are not particles and waves, but has properties of both and neither

James Chadwick

neutron

J.J. Thompson

electron

Rutherford

nucleus, proton

Bohr

shells