Modern Atomic Theory: Subatomic Particles

Atoms are composed of three particles: protons, electrons, and neutrons

History of the Atom:

400 B.C. - Democritus

Greek philosopher who theorized that atoms are the building blocks of matter

atomos = “uncuttable”

300 B.C. - Aristotle

Believed everything was made up of 4 elements: earth, fire, air, and water. Also believed that matter had 4 main properties: hot, cold, dry, and wet.

1803 - John Dalton

English chemist, physicist, and meteorologist. Best known for introducing the atomic theory into chemistry.

1. each element is composed of atoms

2. atoms of each element are identical, but those of different elements are different

3. atoms are neither created nor destroyed

1839 - Michael Faraday

His research concluded with the idea that atoms contain particles with electric charge

1897 - JJ Thompson

British physicist credited with discovering the electron, which was the first subatomic particle to be discovered.

Developed a model where negative particles are stuck in a positively charged ion, called the “plum pudding” model.

1911 - Ernest Rutherford

New Zealand physicist who is known as the father of nuclear physics. Discovered that an atom has electrons scattered at a distance from the small positively charged dense nucleus.

Experiment was called the “Gold Foil”

1913 - N. Bohr

Danish philosopher, promoter of scientific research, and physicist. Developed the “planetary model” of atoms.

Electrons locations are reliant on how much energy they have. Energy levels are located at specific distances from the nucleus.

1926 - Schrodinger

Electrons are found in electron clouds and not paths. They move around the nucleus billions of times in a second.

1932 - James Chadwick

English physicist who discovered that the nucleus of an atom contained a neutral particle with a mass similar to a proton. This particle is called a neutron.