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Lived c. 460 - c. 370 BCE

Commonly thought to be from Abdera, Thrace (Modern Greece), though some say Miletus (Greek city in modern Turkey).

Worked closely with his teacher Leucippus to develop atomic theory. Hypothesized that everything is composed of tiny particles called atoms, which have always and will always exist, are always in motion through a void, and have different shapes and sizes. (Bertrand Russell, A History of Western Philosophy) Believed atoms clung together via hooks on their surfaces. (Ernst Cassirer, An Essay on Man)

Believed atoms had different textures, which explained the textures of the substances they made up: iron atoms were barbed, so they clung together tightly, making iron tough and heavy, water atoms were smooth and slippery, etc. (Jeremy L. Pfeffer and Shlomo Nir, Modern Physics: An Introductory Text)

https://youtu.be/thnDxFdkzZs
(Watch through 1:05)

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Cheerful Democritus - Chalres-Antoine Coypel

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Lived 384 B.C. - 322 B.C, Stagira, Greece.

Known as a great philosopher and was a student of Plato, later teaching Alexander The Great.

Believed in alchemy and that everything (elements) were endlessly divisible (a theory which has been greatly discredited and replaced by chemistry).

He proposed that there were four elements: earth, air, fire, water, (and quintessence) and that things were not made of atoms (he did not believe in the atomic theory proposed by Democritus) but of these four elements.

His theory was partially belived and accepted for many years until more reliable science surfaced.

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Lived 25 Jan. 1627 - 31 Dec. 1691, Lismore, Ireland

Fourteenth child of the first Earl of Cork (Encyclopædia Britannica (11th ed.))

Was an alchemist (Louis Trenchard More, Boyle as Alchemist: Journal of the History of Ideas)

Studied the expansion of water as it freezes. The previous belief was that “cold” was a particle that would get into water as it froze and leave as it warmed up, explaining the expanding of ice. Boyle tested this by weighing a barrel of water, leaving it out overnight to freeze, and re-weighing it, finding it to weigh the same. This caused him to theorize that “cold” is not a particle, and that water simply expands as it freezes, (PBS Nova) paving the way for the study of water molecules in ice.

Published research establishing Boyle’s Law in 1662, showing the inverse relationship between the volume and the pressure of gasses. His experiment involved a J-shaped tube, into which he poured mercury to study the compression of the air trapped at the closed end.

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Joseph Proust is most famous for his discovery of the Law of Definite Proportions, which stated that chemical compounds always combine in the same proportions.

Joseph Proust was born in Angers, France. His father was an apothecary and young Joseph studied Chemistry while working with his father. Proust moved to Paris, where he was the apothecary in chief to the Salpêtrière and taught chemistry with Pilâtre de Rozier. Eventually, Proust moved to Spain, where he taught at the University of Salamanca. When Napoleon invaded Spain, his lab was burned and he was forced back to France. He died in 1826 in Angers, France.

In the world of Chemistry, Proust is most famous for disproving Berthollet[1] with the Law of Definite Proportions. He did this by studying copper carbonate, tin oxides, and iron sulfides.

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Antoine Laurent Lavoisier was largely responsible for making Chemistry into a quantitative science vs a qualitative one.

Lavoisier was a powerful member of many councils and groups.

Antoine Laurent Lavoisier was born into a privileged family. At school and university, while he was attracted to the sciences, he focuses on gaining his law degree, hoping to follow after his father. He did obtain his law degree but decided against practicing law.

Throughout his time studying law, he maintained his interest in the sciences, publishing his first scientific paper the same year he graduated with his law degree. During this time he also read a paper to the highly prestigious French Academy of Sciences. These combined led to him being elected to the French Academy of Sciences in 1769, aged just 26.

After this Lavoisier turned his focus solely towards the sciences. He completed an experiment and study on the law of Mass Conservation using a large diamond and charcoal with a mirror burning the two, which lead him to the discovery of carbon dioxide gas. He also came to the conclusion that the two were the same form of the same element, Carbon, which he named.

Lavoisier, along with Joseph Priestley, was responsible for the discovery of Oxygen. This led him to the idea of combustion, respiration, that respiration is a form of combustion and Oxygens relation to the two.

Lavoisier discovered the Element Sulfur.

After carrying out various studies on various substances, Lavoisier came up with the Law of Conservation of Mass.

While working with Pierre-Simon Laplace, Lavoisier discovered that water was not its own Element, but instead, a compound made up of Hydrogen and Oxygen.

Perhaps what Lavoisier is most famous for is his revolutionary Elementary Treatise on Chemistry. This detailed his Oxygen theory of chemistry and his list of the chemical elements. This Treatise was hugely responsible for pulling Chemistry up onto firmer grounds, even if it contained some inaccuracies.

Later in life, Lavoisier helped develop the Metric system.

During the French Revolution, Lavoisier was sentenced to death for his work with the French government along with some false accusations. He died by guillotine at the age of 50.

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John Dalton is most known for introducing Atomic Theory into chemistry. He is also well known for his research in colorblindness, often called Daltonism.

John Dalton was born in a Quaker family. He learned from his father as well a John Fletcher, a fellow Quaker. His family was unable to continue his education and he went to work for wealthy local Quaker Elihu Robinson. After a period of time, John went to work with his brother running a Quaker school. It was during this time when John would have look more into education, but since he was a Dissenter, he was not encouraged too. He learned mostly from being self-taught and John Gough, a blind philosopher.  He eventually became a professor at a Quaker community where he begin his scientific work, which continued after he left the school.

John Dalton's scientific work into research and work in meteorology, color blindness, gas laws, but his most important work was in Atomic Theory. It is not sure where or when the first idea for Atomic Theory came to him. Even though he was not the first person with a similar idea, John's was novel because he provided a way of calculating relative atomic weights. The principles of this theory remain today.

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Discovered the positively charged protons in the nucleous

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Ernest Rutherford (1871-1937)

Discoveries from 1899

Ernest Rutherford, a physicist from New Zealand who spent most of his career in England and Canada.

Rutherford's gold foil experiment showed that the atom is mostly empty space with a tiny, dense, positively-charged nucleus.

Based on these results, Rutherford proposed the nuclear model of the atom.

All atoms have positively charged particles in the nucleus called protons

If the plum pudding model were true, then the Rutherford hypothesis would have proven the Thompson model correct. However a few alpha particles were deflected in the process. Therefore proving that there is a positively charged nucleus in the center of the atom.

Video- on Earnest Rutherford's contribution to atomic theory

https://www.youtube.com/watch?v=1EdTw4I6L0U

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Plum pudding module where the entire ball is positively charged and only negatively charged electrons exist

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JJ Thomson (1856-1940)

Cathode experiment in 1897

Contribution to atomic theory - Through his experiments with gas particles and a cathode  Thompson discovered electrons, tiny negatively charged subatomic particles within the atom.

JJ Thompson also created the plum pudding model which consisted of negatively charged ions floating in positive “soup”

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Lord William Kelvin lived 1824 to 1907 Between 1870 and 1890 the vortex atom theory was becoming increasingly popular. Lord William Kelvin joined in on the theory where it was believed that an atom had a vortex in the center. This led Kelvin to theorize the knotted atom. Lord Kelvin theorized the knot theory where atoms can have up to 7 crossings in the atoms passing over each other. It was also theorized that each atom knot contained a different element. The knot theory worked with the vortex theory since if all atoms were vortexes then they would pull on each other and cause them to make knotted patterns with the way they are pulling other atoms around.                                                Lord Kelvin also worked with JJ Thomson to put together the first atomic structure.

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James Chadwick discovered the neutron in 1932. A neutron is an atomic particle with no electric charge that makes up an atom’s nucleus.

Chadwick put a piece of beryllium in a vacuum chamber with polonium. The polonium emitted alpha rays, which struck the beryllium. When struck, the beryllium emitted neutral rays.

https://youtu.be/tY7J1Iz0j2o

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Niels Henrik David Bohr was a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory, for which he received the Nobel Prize in 1922.

Bohr travelled to England in 1911 to work with J.J. Thomson at the Cavendish Laboratory, but failed to impress him with his experiments, though he received an invitation for post-doctoral work with Ernest Rutherford.

In 1912 Niels Bohr was working with Ernest Rutherford when he realized Rutherford's model of the atom wasn’t totally accurate. Niels Bohr with the help of Ernest Rutherford discovered that every atom has a nucleus and they all have electrons “orbiting” around the nucleus similar to a solar system, this is known as the Bohr Model. Today the Bohr Model is the most widely accepted model of the atom.

https://youtu.be/uXUqWlcZrss