Atomic Timeline

Democritus

450 BCE

Democritus was a Greek philosopher that believed atoms were uniform, solid, indestructible and moved in infinite numbers through empty space until stopped. He called the atoms "atomos". Him and his mentor are considered the first atomists in the Grecian tradition.

Plato

427 BCE

Plato was a Greek philosopher and he taught Aristotle, another famous philosopher. He created a theory that stated solid forms of matter are composed of indivisible elements shaped like triangles. He believed these are the correct form because they join together to make different shapes.

The Alchemists

500

The Alchemists were a group of people that believed all metals were formed from 2 principles, mercury and sulfur. Alchemists attempted to perfect, purify, and mature certain materials.

Robert Boyle

1662

Robert Boyle was born in London, England on January 25, 1627. He was a philosopher and chemist that believed everything was composed of very tiny particles and was called atomism.

Antone Lavoisier

1789

Antone Lavoisier studied law before going into the field of sciences. He was a chemist that worked on the first periodic table helping with the organization of elements. Lavoisier defined the law of conservation of mass which stated that matter was composed of atoms that were not destroyed or created during chemical reactions.

John Dalton

1803

John Dalton created his theory that stated all matter is made of atoms, all atoms of a given elements are identical, and compounds are combinations of 2 or more different types of atoms. Because of Dalton's achievements, his body was placed in Manchester Town Hall after he died.

Billiard Ball Model

1803

This model was created by John Dalton defining an atom to be in a ball-like structure. Since the ideas of electrons and the nucleus were unknown at the time, the model is just a circle.

Amedeo Avogadro

1811

Amedeo Avogadro was an Italian scientist that created the Gas Law, or Avogadro Law, that stated equal volume of gases at the same temperature and pressure contain the same number of molecules regardless of chemical nature and physical properties. Before discovering his interest in science, Avogadro started to practice as a ecclesiastical lawyer at only 20 years old.

Dmitri Mendeleev

1869

Dmitri Mendeleev was a Russian chemist who created the Periodic Law that states elements arranged according to the value of their atomic weights present a clear periodicity of properties. Mendeleev was given the Davy Medal from the Royal Society of London in 1882 for his achievements.

Pierre and Marie Curie

1898

Pierre and Marie Currie were husband and wife that discovered the energy polonium and radium gave off were particles from tiny atoms that were disintegrating inside the elements. The couple won the Nobel Prize for their research in physics.

JJ Thomson

1900

JJ Thomson began his studies at only 14 years old at Owens College. He was a British physicist that discovered atoms have negative particles called electrons when using a cathode ray tube in an experiment. Thomson proposed the Plum Pudding Model of the atom.

Plum Pudding Model

1904

This model was proposed by J.J. Thomson and represented negatively charged particles, also known as electrons, swim in a sea of positively charged particles. Thomson claims that atoms need positive charges to cancel out the negatives charges of electrons.

Albert Einstein

1905

Albert Einstein was a German physicist that mathematically proved the existence of atoms by the movement of molecules in a liquid. His love for physics all started when his father gift a compass to him when he was a boy.

Robert Millikan

1909

Robert Millikan was born in Morrison, Illinois. He was an American physicist and his work showed that electrons did have a small, defining charge. This allowed the calculation of mass. Millikan measured the charge using oil drops.

Ernest Rutherford

1911

Ernest Rutherford was a New Zealand physicist that described the atom having a tiny, dense, positive charged core called the nucleus. He established mass of an atom is concentrated in the nucleus. Rutherford also demonstrated that their are 2 types of radiation, alpha and beta in 1899.

Henry G. J. Mosely

1913

Henry G. J. Mosely created the Mosely Law stating the square root of the frequency of the x-ray emitted by an atom is proportional to its atomic number, or protons. In 1914, he ended up enlisting in the army when World War I broke out and shortly died a year later by being shot in the head during his service.

Neils Bohr

1913

Neils Bohr was a Danish physicist who created the theory on the hydrogen atom, that stated electrons moved around a nucleus but only in certain orbits and energy is differentiated by radiation. This was based the quantum theory. In 1922, he was awarded the Nobel Prize in physics for his research.

Solar System Model

1913

This model was proposed by Neils Bohr. It describes atoms including a nucleus with a number of electrons in orbits around the nucleus, which is very similar to how the solar system works. Some people think atoms are like tiny solar systems because of this. This model was also known as the Bohr Model.

Electron Cloud Model

1926

This model is proposed by Erwin Schrodinger. The electron cloud is the area around an atom's nucleus where electrons are usually found. The model allowed scientists to make educated guesses on where the electrons were located.

James Chadwick

1932

James Chadwick discovered neutrons which have a neutral charge and is the same mass as a proton. He was awarded the Hughes Medal of the Royal Society in 1932 and in 1935, the Nobel Prize for Physics.