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700 BCE
Asharya Kanada
By mana historians Kanada the Hindu philosopher was believed to come up with the concept of atoms. He thought of this when he was eating food, he kept breaking his food into smaller pieces and realized that the pieces became separated at a linear rate and smaller at an exponential rate. He then theorized that everything on earth is created by smaller pieces, which he called "Anu", and is known today as the atom. -
465 BCE
Empedocles
Empedocles was a philosopher, in ancient times. His mind and philosophies usually revolved around scientific thought, He was mainly known for his theory of natural selection. He theorized that everything on earth was created or made up of four elements, which consisted of earth, wind, fire, and water. Even though in modern chemistry this has been disproven and not taught anymore, this theory was very prominent around his time, and he is known for being one of the first people to study this idea. -
460 BCE
Democritus
Democritus was known as very knowledgeable scientist. He was mainly known for his contribution to his theory, that was everything is made up of small indivisible particles. Which today is called atoms. He with his teachers proposed this idea that went against Empedocles's theory. He also theorized that all theses "atoms" contained different properties, and were all bonded in different manners. -
John Dalton
John Dalton's biggest contribution to chemistry was that he thought all matter is composed of atoms. Even though this theory was first developed by Democritus. Dalton stated that atoms are building blocks of chemical structures and that these atoms can be combined into compounds to form a more complex structure. He then tested his theory with multiple different types of experiments -
J.J. Thomson
J.J. Thomson was mainly known for two things. The first thing was his idea of cathode ray particles, which today are known as electrons. He also discovered that these electrons had a negative charge, and that the mass was very minimal of these electrons. He also knew that atoms were neutral, and so he then showed this with what he mainly has known for the plum pudding model. Which represented the electrons as negatively charged, and the protons as positively charged, displaying the neutral atom. -
Marie Sklodowska Curie
Curie was recognized for her research in radioactivity, and it was her research in radioactivity that created a new study called atomic physics. Marie's theory that the rays from radioactive elements such as uranium were no dependent on the form of the element but rather the atomic structure of the element. -
Nagaoka Hantaro
In general, Hantaro developed the "Saturnian" model in 1904. As postulated in this model, the atom was inherently unstable as the electron would gradually lose energy and fall into the nucleus by constantly radiating. For his model, he predicted two things, one that the atom has a very large atomic nucleus, and electron by electrostatic forces travels around the center. -
Max Planck
Max Planck did not directly affect the atomic theory of matter, his research helped scientists like Bohr to help and expand the atomic theory. His main acknowledgment was that energy radiated in very minimal amounts. He called this theory quanta. -
Albert Einstein
Einstein who was mainly known for his achievments in mathamatics and physics, also had a huge contribution in the atomic theory of matter. He had mathematically proved the existence of atoms, which later led to the general theory of relativity. -
Lise Meitner
Lise Meitner was most known for her studies in nuclear physics, in which she studied about alpha particles and the reaction that the nucleus and the protons and neutrons go through when the nucleus emits an alpha particle. She then discovered that these radioactive recoils can be used to produce very pure elements. -
Ernest Rutherford
Rutherford was known for his amazing model. In his model, it displays the positive charge within the nucleus in the middle, and electrons with negative charges around he theorized that most of the atom is just empty space. He came to this conclusion with his gold foil experiment. -
Niels Bohr
Bohr is mostly acknowledged for his diagram which displayed, different shells of the atom and show where the electrons are kept within the atom. Even so, his main contribution to the atomic theory was a theory for the hydrogen atom which he based on the quantum theory. This theory possibly explains why atoms emit light in fixed wavelengths. -
Louis de Broglie
Louis de Broglie was known for conducting multiple experiments. Through these experiments, he theorized that electrons must contain restrictions on its motion. He then came up with the idea of waves and claimed that it was these waves had properties and boundaries that would restrict the motion of electrons. -
Wolfgang Pauli
Pauli came up with two new and different integers. This formulated the Pauli principle. This principle states that two electrons could not have the same sets of quantum numbers. The Pauli principle is also applicable when it was discovered that protons and neutrons also could be assigned quantum numbers. -
Erwin Schrodinger
Schrodinger came up with the idea of the electron cloud model. Which denies the theory that electrons move in an orbit motion around the nucleus. So then Shrodinger came up with a mathematical equation that informed scientists about the location of the electron. -
Werner Heisenberg
Werner Heisenberg was a mathematical genius. He is remembered for formulating quantum mechanics in terms of matrices and also for discovering the uncertainty principle. This principle states that we can't know the displacement or position of a particle and know the momentum (kilogram*meters/second). Or we can know the position and not the momentum. -
James Chadwick
The main role of James Chadwick in atom theory is that he found the neutron in atoms and that neutrons are located in the middle of an atom, along with the protons, in the nucleus. Neutrons also have neither a positive nor a negative charge but contribute to the same effect as a proton to atomic weight. Chadwick observed this subatomic particle in his experiment using a neutron chamber -
Peter Higgs
Peter Higgs was a physicist, yet still had an impact on the atomic theory. He theorized that all mass is attained through the Higgs field, which created the Higgs boson and leads the creation of quarks. The Higgs boson has just recently begun to be proven right by many chemists and physicists. -
Murray Gell-Mann
Murray Gell-Mann was known for observing protons and neutrons. He then claimed that protons and neutrons are were made up of smaller building blocks, and named these building blocks quarks. This theory was first proven through experiment by taking two atoms and smashing it against each other to see what happens. -
Ronald J. Gillespie
Ronald contributed to the atomic theory, by coming up with the valence shell electron repulsion theory. Which is used in advanced chemistry to determine the future shape based on the number of electron pairs outside the nucleus. -
Richard F.W. Bader
Richard Bader was very experimental, and through his experiments, he discovered that the density of an electron was crucial to explain the behavior of atoms in molecules. He also claimed that there were no orbitals or shells in the molecules. His ideologies were shunned upon as it went against many theories that were accepted in society. Sooner though his theories became more prominent and more accepted by the chemist community.
