History of Atomic Theory Scientists

Events

Democritus

430 BC

Discovered that all matter in the universe is made of atoms and also that atoms will always be in motion. He believed that elemts could be broken down into infinate kinds of atoms, which he called ATOMOS, which is the greek word for uncuttable.

Aristotle

322 BC

Aristotle did not believe in the atomic theory and wanted to prove so. He thought that the Earth was made of 4 elements: Earth, fire, water, and air. His theory was that elements were infinite and could not be broken down.

The Alchemists

400 AD - 1400 AD

People who tried to become rich by turning ordinary materials (like iron or lead) into gold. Their work developed into what is now modern chemistry. Because there were 7 heavenly known bodies, the alchemists believed that there were even base elements. They believed they were wizards and wanted to be able to live forever.

John Dalton

1803

Was the first person to prove whether Democritus or Aristotle was right. He developed the first part of the atomic theory:
1. Matter is made up of tiny particles (atoms) which can all be divided into smaller pieces or destroyed.
2. Atoms of the same element, no matter where, will be exactly the same.
3. Atoms of different elements can combine to form compound elements.
Was the father of the atomic theory.

J.J Thomson

1897

Discovered atoms had negatively charges particles called electrons, while studying atomic structure. He concluded atoms have positive cores and negatively charged particles in it. JJ Thomson believed that an atom was positively charged with negatively charged particles on the inside. Plum pudding model.

Pierre and Marie Curie

1898

Discovered the elements of radium and polonium, during their study in radioactivity. Investigated the nature of high energy rays that are spontaneously produced by certain elements. Found out Radioactivity does not depend on how atoms are arranged into molecules, but rather that it originates within the atoms themselves.

Robert Milikan

1909

He was trying to study the elementary electric charge and the photoelectric effect, did the oil drop experiment, which helped quantify the charge of an electron, to show that electrons are negatively charged

Ernest Rutherford

1911

Studying nucelar physics, noticed the atoms have a core called the nucleus. Conducted gold foil experiment where particles were shot at a gold sheet and marked where they hit. Showed that atoms could not be split. The atom looked like a cherry with a positive center with an empty space.

Niels Bohr

1913

Revised atomic model, thought that electrons were only found in specific orbits around the nucleus. Began studying the properties of atoms. It advanced our thoughts because we thought that they were all over and this shows that they are in different orbits. Bohr's expirement was called the Bohr model.

Erwin Schrödinger

1926

He was studying physics, combined the equations for the behavior of waves with the De Broglie equation to generate a mathematical model for the distribution of electrons in an atom, helped change our view because of the distribution of electrons shifted.