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428 BCE
Plato
Plato was a philosopher during the 5th century BCE. He was a student of Socrates and later taught Aristotle. He founded the Academy, an academic program which many consider to be the first Western university. Plato wrote many philosophical texts—at least 25. -
400 BCE
Democritus
Democritus was a central figure in the development of the atomic theory of the universe. He theorized that all material bodies are made up of indivisibly small “atoms.” Aristotle famously rejected atomism in On Generation and Corruption. -
342 BCE
Aristotle
Aristotle did not believe in the atomic theory and he taught so otherwise. He thought that all materials on Earth were not made of atoms, but of the four elements, Earth, Fire, Water, and Air. He believed all substances were made of small amounts of these four elements of matter. -
400
The Alchemists
Alchemy was based on the belief that there are four basic elements in nature: air, fire, water and earth. Alchemy is an ancient practice shrouded in mystery and secrecy. Its practitioners mainly sought to turn lead into gold, a quest that has captured the imaginations of people for thousands of years. -
Robert Boyle
He discovered that the volume of a gas decreases with increasing pressure and vice versa—the famous Boyle's law. A leading scientist and intellectual of his day, he was a great proponent of the experimental method. -
Lavoisier
Antoine-Laurent Lavoisier, a meticulous experimenter, revolutionized chemistry. He established the law of conservation of mass, determined that combustion and respiration are caused by chemical reactions with what he named “oxygen,” and helped systematize chemical nomenclature, among many other accomplishments. -
John Dalton
Dalton's atomic theory 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. -
Solid Sphere of "Billiard Ball" Model
Because Dalton thought atoms were the smallest particles of matter, he envisioned them as solid, hard spheres, like billiard (pool) balls, so he used wooden balls to model them. -
Dmitri Mendeleev
Russian chemist Dmitri Mendeleev jotted down the symbols for the chemical elements, putting them in order according to their atomic weights and inventing the periodic table. So convinced was he of the soundness of his periodic law that he left gaps for these elements in his table. -
J.J. Thomson
J.J. Thomson's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. Thomson proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged "soup." -
"Plum Pudding" Model
Summary. J.J. Thomson's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. Thomson proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged "soup." -
The Curies
Marie Curie was a physicist, chemist and a pioneer in the study of radiation. She and her husband, Pierre, discovered the elements polonium and radium. They and Henri Becquerel were awarded the Nobel Prize in Physics in 1903, and Marie received the Nobel Prize in Chemistry in 1911. -
Albert Einstein
Albert Einstein is best known for his equation E = mc2, which states that energy and mass (matter) are the same thing, just in different forms. He is also known for his discovery of the photoelectric effect, for which he won the Nobel Prize for Physics in 1921. -
Robert Millikan
His oil drop experiment helped to quantify the charge of an electron, which contributed greatly to our understanding of the structure of the atom and atomic theory. -
Ernest Rutherford
Ernest Rutherford postulated the nuclear structure of the atom, discovered alpha and beta rays, and proposed the laws of radioactive decay. He also discovered the nucleus of the atom. -
Niels Bohr
Niels Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. Electrons should move around the nucleus but only in prescribed orbits. When jumping from one orbit to another with lower energy, a light quantum is emitted. -
Henry G. J. Mosely
He experimentally demonstrated that the major properties of an element are determined by the atomic number, not by the atomic weight, and firmly established the relationship between atomic number and the charge of the atomic nucleus. -
Solar System Model
The Bohr or solar system model of the atom states that atoms consist of a nucleus with a number of electrons in orbits around that nucleus, similar to a solar system. People have speculated that perhaps atoms are tiny solar systems. ... Likewise, perhaps our solar system is an "atom" in some larger entity. -
Werner Heisenberg
German physicist and philosopher who discovered a way to formulate quantum mechanics in terms of matrices.Heisenberg's name will always be associated with his theory of quantum mechanics. For this theory and the applications of it which resulted especially in the discovery of allotropic forms of hydrogen, Heisenberg was awarded the Nobel Prize for Physics for 1932. -
Electron Cloud Model
An electron cloud model is different from the older Bohr atomic model by Niels Bohr. Bohr talked about electrons orbiting the nucleus. The electron cloud model says that we cannot know exactly where an electron is at any given time, but the electrons are more likely to be in specific areas.
