-
460
Democritus's atomic theory
- Discovery date unknown, during lifetime.
- Democritus was born in 460 BCE in Abdera, Greece.
- Democritus theorized all matter was made of tiny indivisible particles called atomos in Greek.
- Democritus died in 370 BCE in an unknown location
-
Antoine Lavoisier proposes the Law of Conservation of Mass
Antoine Lavoisier was born on August 26th, 1943 in Paris France. He was a nobleman who played an important role in discovering the Law of Conservation of Mass in 1789. Licensed to practice law, Lavoisier chose science instead. The man has become known as the "Father of Modern chemistry", and for good reason. He recognized and named hydrogen and oxygen, both of which having to do with his new theory of combustion, and even helped develop the metric system. -
Lavoisier cont.
In 1789, Lavoisier discovered the Law of Conservation of Mass, which stated that mass of a substance before a chemical reaction will equal the mass of the same substance after a chemical reaction. Though this may seem obvious, this idea would revolutionize science. Lavoisier was later executed during the French Revolution on May 8th, 1794. -
Joseph Proust discovers the law of Definite Proportions
- Born on September 26th, 1754 in Angers, France, where he studied chemistry in his father’s apothecary shop.
- Proust created the Law of Definite Proportions in 1806, which stated that a chemical compound always contains exactly the same proportion of elements by mass.
- Died July 5th, 1826 in Angers, France.
-
Dalton's Atomic Theory & Spherical Model
John Dalton was born on September 6th, 1766 in Eaglesfield, England. Dalton became a school teacher at the age of 15, but would later go on to work in science. Working as a mathematics and natural philosophy professor at the “New College” in Manchester, after his teaching days, Dalton developed his atomic theory in 1808. Linking elements to atoms, the Law of Conservation of Mass, and the Law of Definite Proportions, he stated four main ideas for theories: -
Dalton cont. even more
Though this theory and model was partly incorrect, it was one of the first major steps in learning about the atom. Dalton also did extensive research in color-blindness and died on July 27th, 1844. -
Dalton cont.
- All elements are composed of tiny, indivisible, and indestructible particles called “atoms.”
- All atoms of the same element are identical; different elements are different.
- Compounds always have the same relative number and types of atoms.
- Chemical reactions revolve only a rearrangement of atoms. Dalton’s Atomic Theory led him to the spherical model of the atom, one sphere that could not be “broken into smaller parts.”
-
J.J. Thompson discovers the elctron and proposes the Plum Pudding Model
J.J. Thompson was born in Manchester, England on December 18th, 1856, learning at Owens College in Manchester and Trinity College in Cambridge. In 1897, he performed an experiment where he sent electricity through a cathode-ray tube and the gas glowed. When the small cathode ray particles bent toward the positive pole of the magnet, he realized these particles must have a negative charge. He called these particles “corpsucles”, which later came to be known as electrons. -
Thompson cont.
Thompson proposed that all atoms included electrons, and that for the atoms to be neutral, they must also contain a positive charge to cancel out the negative charge. Thompson would later go on to propose the “plum pudding model” of the atom, where tiny negative electrons are embedded in a soft sphere with a positive charge. Thompson had proved atoms were made up of smaller particles that contained charges. Thompson died on August 30th, 1930. -
Max Planck propes his Quantum Theory
- Born on April 23rd, 1858 in Kiel in the Duchy of Holstein. He studied at the University of Munich.
- In 1900, he proposed the quantum theory, which explains the nature of energy down to a sub-atomic level.
- Died on October 4th, 1947
-
Robert Millikan discovers the charge of an electron using the "oil drop experiment."
- Born on March 22nd, 1868 in Morrison, Illinois in the U.S.A. He studied at Oberlin College and Columbia University.
- In 1909, Millikan conducted the oil drop experiment where he was able to determine the charge of an electron is 1.6 x 10 to the negative 19th power coulombs.
- Died December 19th, 1953 in San Marino, California in the U.S.A.
-
Ernest Rutherford publishes Nuclear Model (Planetary Model) of atom
- Born August 30th, 1871 in Brightwater, New Zealand. Studied at Nelson College, Canterbury College, University of New Zealand, and then the University of Cambridge in England.
- In 1898, Rutherford moved to Canada to work at McGill University in Montreal. During the same year, Rutherford coined the terms alpha ray and beta ray to identify two different types of radiation.
- Became chair of physics at University of Manchester in 1907.
-
Rutherford cont. even more
- Rutherford concluded that the atom is mostly empty space, and at the center of the atom was a nucleus.
- The nucleus was mall because of the small number of deflections, and it was also dense because since only something with significant mass could deflect moving particles at such high speed.
- The nucleus has to be positively charged since alpha particles are positively charged and were deflected.
-
Rutherford cont.
-Directed the gold foil experiment in 1909, where associates Hans Geiger and Ernest Marsden fired alpha particles at a thin sheet of gold foil. These particles are positively charged helium nuclei.
- Rutherford believed that most of the particles would be slightly deflected. Instead, most passed right though, only a few were slightly deflected, and very few (1/8000) were greatly deflected.
- Rutherford concluded that the atom is mostly empty space, and at the center of the atom was a nucleus. -
Rutherford cont. for the 4th time
- In 1911, Rutherford published his work and proposed the Nuclear Model of the atom, where the atom is mostly empty space, and a few negative electrons are outside the positive nucleus. It was also called the Planetary Model since the electrons were distributed around the central nucleus.
- In 1920, Rutherford discovered the proton.
- In 1921 while working with Niels Bohr, Rutherford theorized the existence of the neutron. -He died in October 19th, 1937 in Cambridge England.
-
Bohr cont.
- Introduced Bohr’s model in 1913, where negatively-charged electrons move in different fixed orbits that can jump to other orbits surrounding the positively charged nucleus. This was an important contribution to the fields of atomic structure and quantum theory.
- Died November 19th, 1962
-
Niels Bohr proposes Bohr's Model
- Born October 7th, 1885 in Copenhagen, Denmark.
- Studied at Copenhagen University, and then moved to England in 1911.
- Agreed with Rutherford’s idea that electrons move like planets around the sun, but thought they moved in specific circular paths, or in orbits, at different levels, rather than moving randomly around the nucleus.
- Proposed an amount of fixed energy separates on level from another.
- Proposed that electrons could jump from one electron to another.
-
Schrödinger cont.
- The model shows that atoms have energy levels , that the paths are not circular orbits, and that this model can only tell us the probability of finding an electron a certain distance from the nucleus.
- This model was also based of the work of Rutherford, Bohr, and Heisenberg.
- He died on January 4th, 1961 in Vienna, Austria.
-
Erwin Schrodinger proposes the Quantum Mechanical Model
- Born on August 12, 1887 in Vienna, Austria-Hungary. Studied under Frans S. Exner, and later became his assistant.
- In 1926, he developed wave mechanics, and an equation which came to be known as Schrödinger’s Equation.
- This helped him develop a new model of the atom. This model is called the quantum mechanical model (or the electron cloud model) where the electrons, outside the nucleus, are found inside a blurry “electron cloud”- an area where there is a chance of finding an electron.
-
Heisenberg proposes his Uncertainty Principle
- Born on December 5th, 1901 in Wurzburg in the German Empire.
- In 1925, he created the matrix formulation of quantum mechanics with Max Born and Pascual Jordan.
- In 1927, he put forth Heisenberg’s Uncertainty Principle, which stated that it is impossible to calculate both the momentum and location of an electron in an atom.
- Died February 1 1976
-
James Chadwick discovers the neutron and creates the modified nuclear atom model.
-Born on October 20th, 1891 in Bollire, England. He studied at the University of Manchester under Ernest Rutherford.
-In 1932, he discovered the neutron. This discovery leads to the modified nuclear model, which is essentially the same as Rutherford’s original, but instead of a basic positively charged nucleus, the nucleus was made up of positive protons and neutral neutrons.-He was also head of all the British scientists in the Manhattan Project in World War II.
-He died on July 24th, 1974. -
Aristotle's views on atoms.
-Exact date unknown.
-Aristotle was born in 384 BCE in Stagira, Greece.
-Aristotle did not believe in atoms and thought that all matter was made of earth, air, fire, and water.
-Aristotle was believed to be correct at the time, but Democritus was proved correct around 2,000 years later.
-Aristotle died in Chalcis, Greece in 322 BCE.
