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400 BCE
Birth of Atomic Thoery: Early Greek - 400 BCE
Leucippus of Miletus and his student Democritus of Abdera theorized that all matter were made up of small particles. They believed the particles had the following properties:
~They were indestructible
~They were unchangeable
~They were completely solid
These particles were given the name atomos, meaning "indivisible." The particles came in various shapes and sizes, giving it different colours, textures, and taste. -
384 BCE
Aristotle
Democritus' idea was strongly attacked by Aristotle, who lead people to dismiss such an "absurd" idea for many centuries. Aristotle believed that matter was composed of a combination of four elements - Earth, Fire, Water, and Air. This held back the progress of atomic theory and brought a new concept of Alchemy. While it is even less accurate than Democritus' beliefs, it did introduce the idea of elements and them having properties, which play a large role in chemistry up to this day. -
Jan 1, 800
Geber and the Philosopher's Stone - 800 CE
Geber, an Arabian Alchemist, theorized that transmutation between elements was possible - that was to say, by changing the combination of the four elements of a metal, mercury or silver can be combined with sulfur to form gold. This transmutation must be done by the legendary Philosopher`s Stone. It is important to note that alchemy at this time was spiritual, mystic, and philosophical, and hardly scientific. As a fun fact, Geber's name was the origin of the word "gibberish." -
Jan 1, 1200
Albertus Magnus
(Exact Date Unknown)
Albertus Magnus strongly believed in the works by Aristotle and worked extensively to develop his early ideas. He claimed to have witnessed the transmutation of metal to gold and he claimed the possession of the Philosopher's Stone at some point in his life. While most of his "achievements" were questionable, he was credited for being the first to isolate arsenic by heating soap with arsenic trisulphide. -
Jan 1, 1300
The Golden Age of Alchemy
This occurred in the 13th century when Roger Bacon brought alchemy back to life with this famous writings. His ideas were purely spiritual as he believed in creating an elixir from gold that could prolong life. Alchemy became a part of theology and was usually only taught to clergymen. Its popularity lasted for the idea of longevity and the transmutation of cheap metals to gold in times of hardship. -
Jan 1, 1500
Paracelsus
Paracelsus, born in a Swiss family, was a renowned scholar in medicine and believed that alchemy was to cure disease, not transmute metals. He invented the word "alcohol." -
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17th Century Alchemy
Around this era, alchemy split into two categories. Some focused on compounds and reactions while others on the spiritual part of alchemy, as they searched for the transmutation from lead to gold with the help of God. The first is what eventually evolved into the topic that we call Chemistry today. Newton was known to be a famous alchemist at the time! -
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John Dalton
John Dalton of England is known for his development of Dalton's Law, stating that the total pressure of the gases in a system is equal to the sum of the pressures of the individual gases.He also postulated the law of thermal expansion and contraction. However, arguably his number one contribution to the field of chemistry came from the advancements he made in atomic theory, an idea brought from millennia back. -
John Dalton and Atomic Weights
Dalton made a list of the atomic weights of several common elements. This was published as an essay later in 1805, but he never explained as to how he arrived at these numbers until much later. -
A New System of Chemical Philosophy
The issue of atomic weights was readdressed in Dalton's book. Here he emphasized the four main ideas:
~Chemical elements were composed of atoms
~The element can be determined by the mass of the atom
~Different elements have atoms of different masses
~Atoms combined in small whole-number ratios
These ideas were not quite original, but Dalton was able to actually prove many of the ideas by developing a method for calculating atomic masses.
(Exact date of publication unknown) -
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Henri Becquerel
Henri Becquerel, born in France into a family of scientists, was the first to discover radioactivity, which won him the Nobel Prize for Physis in 1903.
Read more -
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JJ Thomson
JJ Thomson, born of England, studied and Cambridge with his research of cathode rays eventually leading to the discovery of the electron. He won the Nobel Prize in Physics in 1906 for his research into the conduction of electricity through gases. -
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Pierre Curie
Pierre Curie was a French physicist who worked with her wife in the development of the new idea of radioactivity. He won the 1903 Nobel Prize, shared with his wife and Henri Becquerel. -
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Marie Curie
Born of Poland, Marie Curie was the first woman to win the Nobel Prize and the only woman to win it twice (in two categories), due to her fascination of radioactivity. She worked with her husband, Pierre Curie, to continue the research of radioactivity. The element Curium is named in her and her husband's honour. -
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Ernest Rutherford
Born in Zealand, Rutherford was a physicist and chemist that was one of the first to bring about the idea of radioactivity. He won the 1908 Nobel Prize for Chemistry for his theory of atomic structure. Despite his contributions to the atomic model and radioactivity, he was deeply unsettled as he feared that such a discovery will lead to the use of nuclear weapons, which did become a reality. The element Rutherfordium was named in his honour. -
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Niels Bohr
Born in Denmark, Bohr studied under both Thomson and Rutherford and revolutionized scientific progress with his theory on atomic structures and radiation. Taking part in the Manhattan Project in the 1930s, he actively called for agreements that nuclear energy be used for peaceful applications, despite being met by some resistance, and won the Atoms for Peace Award of 1957. He helped to establish CERN in 1954. -
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James Chadwick
James Chadwick was an English researcher who studied under Rutherford. He was credited the discovery of the neutron and received the Nobel Prize for Physics in 1935. He also took part in assessing the feasibility of the Manhattan Project, claiming he couldn't sleep at night knowing the inevitability of a nuclear war. -
Henri Becquerel's Discovery of Radioactivity
Henri Becquerel noticed that the uranium in phosphorescent crystals created images (silhouettes) on a photographic plate. He was surprised when this continued a week later, as he couldn't identify the source of radiation. He determined it had to be from within the substance itself, and this mysterious radiation was named "radioactivity." -
Thomson Discovers the Electron
(Exact Date Unknown)
Thomson set out to solve the problem of cathode rays, which occurred when an electromagnetic current is sent through a tube which is pumped to almost a vacuum. The ray behaved like a particle, and had the same mass to charge ratio regardless of the gas used. He was able to conclude from his experiments that these rays were negatively charged particles with 1/2000 times the mass of a hydrogen atom, which he called "corpuscles," later named the electron. -
1903 Nobel Prize in Physics - Radioactivity
Continuing the discovery of radiation, Becquerel made further studies with beta particles, which he confirmed to be the same as electrons, as proposed by Thomson. He also helped discover that the element of an atom can change due to radiation. All of his work lead him to winning the 1903 Nobel Prize for Physics, shared with Marie and Pierre Curie who had also contributed to the development of this new concept. -
Thomson's Nobel Prize
Thomson was awarded the Nobel Prize in Physics "in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases," as part of his investigation of cathode rays and the electron. -
Rutherford's Nobel Prize
Rutherford's research at Cambridge led him to the discovery of the various particles emitted from radioactivity. While his Nobel Prize was awarded in 1908 for the discovery for the disintegration of atoms and the release of alpha, beta, and gamma emissions, yet his main contribution to chemistry occurred the year after, when he began his famous gold foil experiment. -
Rutherford's Atomic Model
(Exact Date Unknown)
Rutherford's gold foil experiment was to fire alpha particles at a gold foil to see how they pass. Most of the particles went straight through the foil, but some were deflected off course. Rutherford concluded that such a strong repulsion can only be accounted for by a dense, positively charged nucleus. This idea fits into Thomson's idea of the electron neutralizing the atom's charge, yet could not explain the source of the excess mass in atoms resulting from neutrons. -
Marie Curie's Second Nobel Prize and Later Years
Marie Curie became the first woman to win two Nobel Prizes, this time in Chemistry for the discovery and extraction of two new elements, Radium (88) and Polonium (84). Polonium was named after her home country, Poland. She continued to help out with World War I after, by organizing a fleet of X-ray machines for doctors to use up front. Following the war, she raised money to build the first radium research institute in Warsaw. -
Thomson Discovers Isotopes
(Exact Date unknown)
In 1912, Thomson experimented by firing ionized neon through a magnetic and electric field, which oddly resulted in two distinct deflections. His only explanation was that neon could have two different masses, proving one of Dalton's claims to be wrong and resulting in the discovery of isotopes. -
Bohr's Nobel Prize in Physics
Niels Bohr received the 1922 Nobel Prize in Physics for his theory of atomic structures. He quantized the concept of electrons and expanded on the atomic model by proposing that electrons moved in certain orbital shells, with the outer shells having higher energy. Furthermore, it was the outer shell that determined the properties of the element, as is what determined the shape of the present day periodic table. He strengthened Rutherford's Atomic Model and set the basis for quantum mechanics. -
The Discovery of the Neutron
(Exact Date Unknown)
The final subatomic particle, the neutron, was discovered by James Chadwick when he was studying the effects of bombarding beryllium with alpha particles. This resulted in the release of a radiated particle that had similar a mass to the proton but no charge, which he concluded had to be making up the mysterious extra mass present in atoms. This discovery provided a new tool for observing atomic structure, as neutrons won't be deflected by the positively charged nucleus.
