-
700 BCE
Asharya Kanada
It is assumed that Acharya Kanad was the first to understand the concept of an indestructible substance particle. The theory came to Kanad when he walked with food in his hand and cut it into small pieces. He did so until he could no longer split it up into smaller pieces. It was then that he knew that he could not split the food into other sections and that he was talking about the notion of a particle that could not be further divided. He called the "Anu" or atom of the particle. -
450 BCE
Empedocles
Empedocles lived in ancient times during the dawn of scientific thought, and his most significant contribution to atomic theory is probably his theory of natural selection, in which he suggested that the four elements (Earth, Wind, Fire, Water) make up everything. He was one of the first people to try to divide nature into different elements, even though his theory is disproved. -
420 BCE
Democritus
Democritus is attributed to one of the first people to say that all things are made up of small, geometrically indivisible particles that he called "atoms." Together with his teacher Leucippus and Epicurus, Democritus proposed the idea of how all things are made up of atoms and the various properties each element has to do with the form of the atom and how it is bonded. -
John Dalton
The contribution of John Dalton to the atomic theory is that he theorized that all matter is made up of atoms. Now the concept belongs to Democritus initially, but Dalton is the first to construct a modern atomic theory definition. In which he notes that atoms are fundamental building blocks of chemical structures and that each chemical element is made up of atoms, and these atoms can be combined to create a more complex structure through experiments in which he came to the realization. -
JJ Thomson
Thomson's innovations began with his cathode ray tubes experiments. Thomson came up with the idea of the electron he labeled cathode ray particles using his experiment. He concluded through his experiment that the particles must be charged negatively and their mass is very small. Thomson understood that atoms were neutral and he extended the concept of Dalton by developing the plum pudding system where the atoms pudded with negative and positive charges. -
Marie Sklodowska Curie
Through her work on radioactivity, Curie contributed to the atomic theory. Curie researched uranium rays when she believed that the rays did not depend on the shape of the uranium, but on its atomic structure. Her theory created a new field of study, nuclear physics, and Marie invented the term "radioactivity" herself. At the time, she described radioactivity as this activity of rays based on the atomic structure of uranium, the number of uranium atoms. -
Nagaoka Hantaro
Notably, in 1904, Hantaro created the "Saturnian" method. As postulated in this model, the atom was inherently unstable as the electron would gradually lose energy and fall into the nucleus by continually radiating. With his model, he predicted two things, one that the atom has a very massive atomic center, and electron by electrostatic forces revolves around the center. -
Max Planck
While Max Planck did not precisely influence the theory of the atom, his observations helped other scientists, including Neils Bohr, to develop the theory of the atom. His key results were that energy was radiated in discrete quantities which he called quanta, a theoretical description of the spectrum radiation emitted by an object which glows when heated. -
Albert Einstien
The contribution made by Albert Einstein to the atomic theory was that he confirmed the existence of atoms mathematically. He presented his paper on the Special Theory of Relativity that same year, which later led to the General Theory of Relativity. -
Lise Meitner
Meitner and Hahn discovered radioactive recoil, discovering that when an alpha particle is released by an atomic nucleus, the nucleus would recoil like a weapon that fired a bullet. The positively charged nucleus recoiling may be drawn to an electrode that is negatively charged. Meitner and Hahn have shown that radioactive recoil can be used to generate very pure elements and store them on the negative electrode. -
Ernest Rutherford
The nuclear model of the atom was Rutherford's significant contribution to the atomic theory. In which he defines the positive charge, the negative charges around it are in the center of the atom, and most of the atom is nothing but space. Via his gold foil experiment, he came to this discovery where he fired alpha particles on a thin sheet of gold and found how not all alpha particles move through the layer of gold. -
Niels Bohr
The contribution of him was that he proposed a theory for the hydrogen atom based on the quantity theory that only certain well-defined quantities of energy are transferred. Only in prescribed orbits should electrons pass around the nucleus. A light quantum is released when moving from one orbit to another with lower energy. The theory of Bohr may explain how atoms in fixed wavelengths emitted light. -
louis de Broglie
Experiments in the early 20th century had shown that the electron had to travel around a nucleus and that and that its mobility was limited. The notion of a particle with a wave's properties explained the restricted motion by De Broglie. A wave contained within limits imposed by the nuclear charge would be constrained in form and therefore in action, because any wave shape that did not fit within the atomic boundaries would conflict with itself and be canceled. -
Wolfgang Pauli
As Wolfgang Pauli invented two new numbers and proposed the Pauli rule, which stated that no two electrons in an atom could have similar quantity sets, he contributed to the atomic theory. It was later discovered that quantity numbers could also be allocated to protons and neutrons in nuclei and that the method of Pauli also applied here. -
Erwin Schrodinger
Schrödinger suggested the concept of the electron stream, which no longer shows electrons traveling in an orbit around the nucleus. Alternatively, Schrodinger proposed a model that would only allow scientists to make educated guesses about electrons ' positions. Therefore, their locations could only be represented as part of a' wave' around the nucleus where they are likely to find the electrons. -
Werner Heisenberg
Through formulating quantum mechanics in terms of matrices and also introducing his uncertainty principle, Heisenberg contributed to the atomic theory. In which he states we can know a position of particles, but it's not momentum, or we can know it's momentum, but it's not position. -
James Chadwick
James Chadwick's leading role in atomic theory is that he found the neutrons in the atoms and that the neutrons are located in the middle of the atom in the nucleus, along with the protons. Neutrons also have neither a positive nor a negative charge but contribute with the same effect as a proton to atomic weight. By using a neutron chamber in his experiments, Chadwick discovered this subatomic particle. -
Peter Higgs
Higgs added to the atomic theory by theorizing that how particles interact with something he called the Higgs field produced by the Higgs boson would gain all mass. He was not taken seriously at the time but was given light as a source of the particle accelerators with the upcoming but recently. -
Murray Gell Mann
When a lot of new elementary particles were identified by new accelerators and apparatuses. Murray Gell-Mann described particles and their interactions in theoretical works of the same time. He proposed that observed particles were possibly composite, i.e. made up of smaller building blocks called quarks. According to this theory, there should be as yet undiscovered particles. He first explained how the quarks are made up of protons, neutrons. -
Ronald J.Gillespie
By creating the widely used theory of Valence Shell Electron Pair Repulsion (VSEPR), Gillespie contributed to the atomic theory. Predicting the shape based on the number of pairs of electrons in the outer shell. -
Richard F.W Bader
Richard Bader discovered that in understanding the action of atoms in molecules, electron density is very important. According to his theory, the molecules do not contain atomic orbitals. This was a new idea that went against ideas that were accepted. He fought hard for and found it hard to publish his revolutionary ideas. Eventually, the ideas became more accepted and a book Atoms in Molecules, a 1991 Quantum Theory, was published.
