History of Atomic Theory

Kashyapa Kanada

600 BCE

Kashyapa Kanada proposes that paramanu (atom) is an indestructible particle of matter. The atom is indivisible because it is a state at which no measurement can be attributed. His proposal of atoms helped us to further develope the structure of atoms

Alchemists

500 BCE

Alchemy is the art of discovering and understanding different matters. Alchemy contributed to the atomic theory, by laying down a great foundation of the modern-day periodic table of the
elements and enables us to further discover the world of chemistry.

Ancient Greek

5 BCE

The idea of all matter is made up of tiny, invisible particles, also known as atoms, is believed to have originated with the Greek philosopher Leucippus of Miletus and his student Democritus of Abdera in the 5th century B.C

Dalton

1803

Dalton proposed that all matter was composed of atoms, indivisible, and indestructible building blocks. While all atoms of an element were identical, different elements had atoms of differing size and mass. Dalton also stated that all compounds were composed of combinations of these atoms in defined ratios. His theory of atoms eventually helped us to understand the construction of an atom and thus contribute to the atomic theory.

Hantaro Nagaoka

1895

Hantaro Nagaoka proposed an alternative planetary model of the atom in which a positively charged center is surrounded by a number of revolving electrons. His discovery on which the electrons are surrounding in positively charged atoms eventually led to the idea that electrons are surrounded in orbitals and give us a better understanding of the construction of an atom; therefore,
has a great impact on the atomic theory development

Max Planck

1900

Max Planck was a German scientist who first discovered that energy is emitted from a black body in discrete amounts called quanta. He showed that the amount of energy was proportional to the frequency of the radiation that was absorbed by the black body, a relationship now known as Planck's Law. His discovery eventually advances our understanding of the atomic structure. (electrons because they also have different energy levels)

Thomson

1904

Thomson’s experiments with cathode-ray tubes showed that all atoms contain tiny negatively charged subatomic particles – also known as electrons. His experiment helped us to understand the composition of an atom and thus further developed atomic theory.

Rutherford

1908

Rutherford proposed that major space in an atom is empty. He also concludes that the positive charge in an atom is not distributed uniformly and it is concentrated in a very small volume from
his gold foil experiment. Later known as the nucleus.

Albert Einstein

1909

Einstein demonstrated that electromagnetic radiation, including light, has the characteristics of both a wave and, consistent with Planck's theory, a particle.

Bohr

1913

Niel Bohr’s atomic theory states that – an atom is like a planetary model where electrons were situated in discretely energized orbits. His discovery allows us to further develop our understanding on electrons.

Louis de Broglie

1924

Louis de Broglie discovered the wave nature of electrons and suggested that all matter have wave properties. His discovery allows people to further understand the structure and properties of electrons.

Werner Heisenberg

1925

Werner Heisenberg contributed to atomic theory through formulating quantum mechanics in terms of matrices and in discovering the uncertainty principle, which states that a particle's position and momentum cannot both be known exactly.

Wolfgang Pauli

1925

Wolfgang Pauli contributed to atomic theory by discovering the Pauli exclusion principle, which states that in an atom no two electrons can occupy the same quantum state simultaneously. Therefore, he is simply stating that no two electrons are similar – they are always different.

Erwin Schrödinger

1926

Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the quantum mechanical model of the atom. His discovery allows us to further understand the behaviors of electrons.

James Chadwick

1932

James Chadwick played a vital role in the atomic theory, as he discovered the Neutron in atoms. A neutron is a particle with no electric charge that, along with positively charged protons,
makes up an atom’s nucleus.

Lise Meitner

1938

Lise Meitner discovered that nuclear fission can produce enormous amounts of energy. She made the discovery in Sweden, after escaping a few months earlier from Nazi Germany. When World War 2 ended, she was acclaimed as the mother of the atom bomb. She had great contributions to the nuclear field (theoretical chemistry field)

Dorothy Crowfoot Hodkin

1964

Hodgkin’s most significant scientific contributions were the determination of the structures of penicillin, insulin, and vitamin B12. In 1964 she won the Nobel Prize in Chemistry “for her determinations by X-ray techniques of the structures of important biochemical substances.” She was the third woman ever to win the prize in chemistry

Ronald James Gillespie

1972

Gillespie explored the chemistry behind the brightly coloured solutions produced when certain elements were dissolved in concentrated sulfuric acid. In the process, he developed superacids, such as HSO3F, which became widely used in organic and inorganic chemistry. This development led to the production of non-metallic elements in the form of polyatomic cations a discovery that opened up a whole new field of chemistry.

Richard F.W. Bader

1991

Richard Bader states that there are no atomic orbitals in the molecules. His new idea resulted in many debates after it was proposed. However, his idea eventually led scientists onto the
correct route of finding the atomic orbital theory and thus have a great contribution to the general understanding of atoms as well