History of Chemistry

democritus

believed the world was made of 2 things-

• empty space

• tiny particles called atomos, which he considered to be the smallest particle of matter

john dalton

• developed the Atomic Theory

• Discovered that the same elements have the same kinds of atoms

• Discovered elements have different kinds of atoms

• Studied works of other scientists (Lavoisier and Proust) and developed his own theory.

Thomson

• Discovered electrons while conducting research using Cathode Ray

• Discovered when an electrical current passed through the Cathode tube, it glowed (he called it the Cathode Ray).

• Found the Cathode Rays deflected away from negatively charged objects.

• Called these negatively charged objects “electrons”; believed to be mixed in with positive protons.

cathode ray

a glass tube filled with a gas at a low pressure

Rutherford

• Bombarded a piece of thin, gold foil (Gold foil experiment) with alpha particles which have a positive charge.

• Noticed some particles bounced back towards the source, indicating something was solid inside.

• Concluded the mysterious object was a densely packed bundle of positively charged matter (protons) that he called “nucleus”

Bohr

• discovered that electrons are arranged in energy levels around the nucleus (not in true circles)

• This keeps the negatively charged electrons from being pulled into the positively charged nucleus.

Schrödinger

• used a matter wave theory to develop a probabilistic model of the atom.

• Ne discovered electrons don’t follow sharply defined objects but are found in orbitals.

• constructed the equation that led to the discovery of the shapes of the orbital.

Chadwick

• discovered the neutron

• discovered a neutral form of radiation that had to be emitted from a neutral particle in an atom