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Democritus
Democritus was the first scientist to create a model of the atom. He was the first one to discover that all matter is made up of invisible particles called atoms. He created the name "atom" from the Greek word "atomos", which means uncuttable. He also discovered that atoms are solid, insdestructable, and unique. HIs model was just a round solid ball. In 400 B.C.. -
Antoine Lavoisier
Lavoisier founded several elements and put the first table of elements together. He used Aristotle's ideas of fire, earth, air, and water to create experiments invesigating combustion and oxidation. By using previous knowledge of atomic bonding, he discovered important elements like oxygen, hydrogen, and sulfur. He discovered that water was made of oxygen and hydrogen, and air included nitrogen. -
Law of conservation of mass
Law of Conservation of Mass is a relation stating that in a chemical reaction, the mass of the products equals the mass of the reactants. Established in 1789 by French Chemist Antoine Lavoisier
States that mass is neither created nor destroyed in any ordinary chemical reaction. -
John Dalton
John Dalton was an English chemist that created the Atomic Theory of Matter, a composition of previous findings by Democritus and his own findings. He included in this theory that all matter is made of atoms, that atoms cannot be created nor destroyed and also, atoms of different elements combine in whole ratios to form chemical compunds. His theory would later contribute to an advance in the atomic model. -
Dalton's Atomic theroy
John Dalton created the Atomic Theory of Matter, a composition of previous findings by Democritus and his own findings. He included in this theory that all matter is made of atoms, that atoms cannot be created nor destroyed and also, atoms of different elements combine in whole ratios to form chemical compunds. His theory would later contribute to an advance in the atomic model. He also wrote the first symbols for the elements. -
Dmitri Medeleev
Created the first periodic table. -
J.J. Thomson
Up until his time, all models of the atom looked like a big solild ball. J.J. Thomson discovered the electron, which led him to create the "plum pudding" atomic model. In this model, he thought that the atom was mostly positive, and negative electrons wandered around the atom. The "plum pudding" model influenced other scientists to make better atomic models. -
plum pudding atomic model
In Thomson’s "Plum Pudding Model" each atom was a sphere filled with a positively charged fluid. The fluid was called the "pudding." Scattered in this fluid were electrons known as the "plums." The radius of the model was 10-10 meters. -
Ernest Rutherford
Ernest Rutherford was another scientist that changed the atomic model. He felt that J.J. Thomson's model was incorrect, so he created a new one. He created the nucleus, and said that instead of the positive matter being the whole atom, it was just in the middle. He said the atom was mostly empty space and that the electrons surrounded the positive nucleus. This model influenced one of his own students to perfect the atomic model later on. -
Robert Millikan
Robert Millikan is most notable for his discovery of the actual charge of the electron. J.J Thompson had already discovered the charge-to-mass ratio so the calculation of the charge directly resulted in the calculation of the mass of the electron. This allowed them to better understand the charges taking place within the atom. -
Gold foil experiment
The Rutherford Gold Foil experiment shot minute particles at a thin sheet of gold. It was found that a small percentage of the particles were deflected, while a majority passed through the sheet. This caused Rutherford to conclude that the mass of an atom was concentrated at its center. -
Niels Bohr
Niels Bohr was a Danish scientist that was a student of Rutherford. He decided to make a new model based off of Rutherford's model, but changed the orbit of the electron. Also, he created energy levels in the atom, where only a certain amount of electrons could fit on one energy level of the atom. Bohr also used Planck's ideas in order to create quantum mechanics, his new concept regarding energy. This model is still used to this day. -
Henery Moseley
Henry Mosely was an English scientist who worked with Niels Bohr in order to create the real atomic number. Mosely used X-rays to find the frquencies of elements on the periodic table. Before his discovery, the atomic number was just an assigned number to a random element. Mosely used these frequencies to find that the number of protons in the nucleus correlated with the atomic number. This created Mosley's Law. The image to the left is one of Mosely's periodic tables. -
bhor's planetary model
In 1913 Bohr published a theory about the structure of the atom based on an earlier theory of Rutherford's. Rutherford had shown that the atom consisted of a positively charged nucleus, with negatively charged electrons in orbit around it. Bohr expanded upon this theory by proposing that electrons travel only in certain successively larger orbits. He suggested that the outer orbits could hold more electrons than the inner ones, and that these outer orbits determine the atom's chemical properties -
Erwin Schrodinger
Erwin Scrhodinger was an Austrian scientist that worked with the Quantum model of the atom. He disagreed with Bohr's theory, so he created his own. He thought that the only way to find the location and energy of an electron in an atom was to calculate its probability of being a certain distance from the nucleus. This equation influenced the Quantum mechanical model of the atom. Came up with the electron cloud method. -
Quantum mechanical model
Erwin Scrhodinger was an Austrian scientist that worked with the Quantum model of the atom. He disagreed with Bohr's theory, so he created his own. He thought that the only way to find the location and energy of an electron in an atom was to calculate its probability of being a certain distance from the nucleus. This equation influenced the Quantum mechanical model of the atom. -
Electron cloud method
The electron cloud model is an atom model wherein electrons are no longer depicted as particles moving around the nucleus in a fixed orbit. Instead, as a quantum mechanically-influenced model, we shouldn’t know exactly where they are, and hence describe their probable location around the nucleus only as an arbitrary -
James Chadwick
Chadwick proved the existance of neutron. He discoverd a particle within the nucleus that has a mass similar to that of a proton. -
cathode raya tube
Electrons are distributed throughout uniformly charged positive sphere of atomic dimensions. J.J. did not like the term electron. He called the electron, the "corpuscle" of electrical charge. Another British electrochemist John Stoney called it the "electron" from the Greek term "Elecktra" which is the Greek word for amber. Amber when rubbed builds up static charge.
