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400 BCE
400 BC/BCE: Democritus proposed the idea of the "atom"
Democritus was an ancient Greek philosopher. He developed the concept of an atom, which is a Greek word that means "indivisible". He believed that everything in the universe was made up of microscopic particles that were indestructible. This belief later led to the development of the atomic theory. -
340 BCE
340 BC/BCE: Aristotle formulated his own theory of the elements of matter
Aristotle was a Greek philosopher and scientist who believed that all materials on Earth were not made of atoms, but of the "four elements of matter", Earth, Fire, Water, and Air. He believed all substances were made of small amounts of these four elements of matter. Many years later, other scientists continued to expand on Aristotle's theory of the elements and realize that matter is made of atoms. -
762
750-800: Abu Musa Jabir ibn Hayyan created distillation and crystallization methods
Abu Musa Jabir ibn Hayyanwas or "the father of Arab chemistry" was an Islamic alchemist, pharmacist, philosopher, astronomer, and physicist. He was able to create simple crystallization and distillation methods. It is unclear when these discoveries were made but it is believed to be somewhere around 762. These crystallization and distillation methods are commonly used today and can help scientists separate substances. -
1250
1250: Magnus discovered arsenic
Magnus was a German scientist who discovered the element of arsenic. This was discovered when he heated soap together with orpiment. This discovery later led to more discoveries of elements, which can combine to make matter. -
1440
1440: The printing press was invented
The printing press was invented by Johannes Gutenberg. This technology allowed many scientific works to be officially published. -
1654: The vacuum tube and electric generator were invented
The Vacuum tube and electric generator were invented by a German scientist named Otto von Guericke. This invention was helpful to increasing studies of air particles and air pressure. -
1662: Robert Boyle formulated Boyle's Law
Boyle was an Anglo-Irish philosopher, chemist, physicist and inventor. He discovered that the pressure of a given quantity of gas is the inverse of it's volume at constant temperature; pv = k.
(Boyle's Law). This law is constantly being used in studying chemical reactions or anything using gases. -
The Early 1700's: The precision balance was invented
The precision or analytical balance was invented by early Egyptians. Historians say that it was invented sometime around 1700. This balance is used in modern chemistry frequently. -
1766: Cavendish discovered hydrogen
Cavendish was a philosopher, chemist, and physicist. He is known for the discovery of hydrogen, or as Cavendish called it: "inflammable air". He realized that hydrogen gas is a discrete substance. This discovery allowed for the discovery of the three states of matter; solids, liquids, and gases. -
December 9, 1787: French Chemist Antoine Lavoisier
In December of 1787, Lavoisier established the Law of Conservation of Mass.The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction. He also conducted a careful study of the burning process which resulted in his proposal of the Combustion Theory which was based on sound mass measurements. Lavoisier began the conversation of what an atom actually is. -
1803: John Dalton proposed the atomic theory
John Dalton was an English chemist, physicist, and meteorologist. He created the atomic theory. This theory states that all matter is made of atoms that are indestructible and indivisible. In addition to proposing the atomic theory, Dalton also discovered that compounds are formed by a combination of two or more different kinds of atoms. Dalton's discoveries enabled other scientists to figure out the basic building blocks of matter and chemical reactions. -
1811: Avogardo proposes his molecular theory which eventually became "Avogardo's Law"
Avogordo was an Italian scientist & is most well-known for his contribution to the molecular theory, which is now known as Avogadro's law. This law states that "equal volumes of all gases, at the same temperature and pressure, have the same number of molecules".He developed "Avogardo's number"(6.022×10 23) which means that the mass of a mole of a substance is equal to that substance's molecular weight. This discovery expanded the molecular theory & allowed a better understanding of molecules. -
1869: Mendeleev proposed periodic law
Dmitri Mendeleev was a Russian inventor and chemist. He proposed his own periodic law that states: "when the elements are arranged in order of increasing atomic mass, certain sets of properties recur periodically." This discovery led to the arrangement of the periodic table of elements. -
1879-1897: JJ Thompson discovered and identified electrons and the first subatomic particles.
Thompson was an English physicist who is most famous for his discovery of the first subatomic particles and his identification of electrons. He clarified the idea that Dalton's atoms are not the
fundamental particles of nature, but pieces of even smaller particles.In addition to his first two discoveries, he also is responsible for the discovery of isotopes. This led to a better understanding of molecules and added to the atomic theory that there are smaller particles that make up an atom. -
1894-1898: Ramsay discovered Noble gases and three elements
William Ramsay was a British chemist who is responsible for the discovery of the noble gases among the elements. Additionally, Ramsay discovered three new elements; neon, krypton, and argon. This discovery later helped the format of the periodic table to be made and more elements to be studied and discovered. -
1898: The Curies discovered radium and polonium.
Marie and Pierre Curie Pierre spent many years studying radioactivity. This led to the discovery of the elements radium and polonium. -
1911: Rutherford created the model of the atom
Ernest Rutherford was a physicist from New Zealand who came to be known as the father of nuclear physics. He was the first to discover that atoms have a small, charged nucleus and are circled by tiny electrons. This is what is known as the Rutherford model(the model of the atom). Rutherford also contributed further by naming the "proton" for the positively charged particles in the nucleus of an atom. Rutherford's breakthrough is now a part of the basis of the atomic model. -
1913: Bohr proposed a theory for the hydrogen atom
Bohr was a Danish physicist who made many contributions to understanding atomic structure & the quantum theory. Bohr proposed that "energy is transferred only in certain, well defined quantities, electrons move only in prescribed orbits around the nucleus, and when jumping from an orbit to another with lower energy, a light quantum is emitted. The number of electrons in the outer orbit determines the properties of an element. The atomic model was officially formed after Bohr's discovery. -
1924: Louis de Brogile discovered the wave patterns of electrons
Louis de Broglie is a French physicist who studied the wave patterns of electrons and proposed that all matter has wave properties. De Brogile spent time researching the quantum theory and then was able to predict "the wave nature of electrons". This breakthrough was beneficial to the study of matter and helped scientists dig deeper into the subatomic particles of the atom. -
1925: Heisenberg formulated the theory of quantum mechanics.
Heisenberg was a German physicist and philosopher. He is most famous for his theory of quantum mechanics which compares smallest scales of energy levels of atoms and subatomic particles. This theory later led to the discovery of allotropic forms of hydrogen. -
1926: Schrodinger developed the quantum mechanical model of the atom
Schrodinger was an Austrian physicist. He added to the Bohr atom model and developed the quantum mechanical model of the atom. He was able to formulate and use equations to describe the likelihood of finding an electron in a certain position in an atom. Schrodinger and Bohr's work greatly contributed to the atomic theory because together, they developed the atomic model. -
1932: Chadwick discovered neutrons in an atom
James Chadwick discovered that neutrons are located in the center of an atom with the protons. They have neither a positive nor negative charge, but contribute the the atomic weight with the same effect as a proton.This is now one of the principles of the atomic model and allowed many other scientists to add to this model and theory. -
1934: Artificial radioactivity was discovered by Irene and Frederic Joliot-Curie
Irene Joliot-Curie was the daughter of Pierre and Marie Curie. She was a French chemist who discovered artificial radioactivity with her husband, Frederic. This discovery led to further study of using radiation. An example is the use of radiation to cure cancer. -
December of 1938: Meitner discovered nuclear fission
Meitner was an Austrian-Swedish physicist who studied radioactivity and nuclear physics. She is also responsible for leading the small group of scientists who first discovered nuclear fission; specifically of uranium. Meinter's discovery of nuclear fission allowed further studies into what happens to matter during nuclear fission and chemical reactions. -
1950's: Proteins were discovered by Linus Pauling
Pauling was an American chemist, biochemist, author, and teacher. In 1954, he was awarded the Nobel Prize in Chemistry. In the 1950's he also became known as the founder of molecular biology. He is awarded this title and the Nobel prize for the discovery of proteins. His studies and research eventually contributed to the breakthrough of the double-helix DNA model. -
1952: Franklin discovered the shape of DNA molecules
Franklin was an English chemist. She contributed to Watson and Crick's DNA model by stating that DNA is shaped like a "twisted ladder". Franklin's discovery later contributed to the DNA model and further studies conducted on DNA.
