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400 BCE
The Egyptians successfully revolt against Achaemenid Persians after being conquered by them for 150 years.
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400 BCE
Democritus discovers that the atom exists and is the building block of matter.
This discovery enabled people to realize that there was a small, constant particle which is the smallest unit of matter. Even though the atom could not be seen, Democritus recognized its existence sparking thought about it in later years. -
400 BCE
Democritus is born
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370 BCE
Democritus dies
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John Dalton is born
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Michael Faraday is born
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America purchases the Louisiana territory from France. The size of the United States was doubled.
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Dalton discovers his atomic theory
Dalton’s atomic theory states that all matter is composed of indivisible, indestructible atoms with distinct properties that determine their characteristics. It formed a basis of understanding for atomic research going forward. His "marble model" portrays the atom as a sphere with the same particles throughout. -
Faraday discovered that atoms have an electrical component.
This realization of an atom’s electromagnetic charge was significant to learning about different unknown parts of the atom and how they interact. -
John Dalton dies
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Eugene Goldstein is born
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JJ Thomson is born
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Michael Faraday dies
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Robert Millikan is born
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Ernest Rutherford is born
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Niels Bohr is born
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Using a cathode ray tube, Goldstein discovered that atoms contained positively charged particles.
This led to the discovery of the proton, majorly contributing to the atomic model by adding to understanding of the nucleus. -
Erwin Schroedinger is born
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James Chadwick is born
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JJ Thomson discovered that atoms contain negatively charged subatomic particles, or electrons. He theorized that they were embedded within the larger field of positively charged particles like in a soup.
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The Philippine-American War begins over Philippine land annexed by the Treaty of Paris.
After 3 years, the war ended with the Philippines becoming a US territory. -
Werner Heisenberg is born
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Since the concept of electrons had already been discovered, Millikan was able to determine the magnitude of an electron’s negative charge. He also discovered that they all have the same amount of charge
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Rutherford discovered that the atom consisted of mostly empty space with most of its mass existing in the positively charged nucleus.
His discovery led to the formation of the “nuclear model”, also known as the “Jimmy Neutron” model which is common today. -
Bohr discovered that electrons orbited around the nucleus in a specific pattern.
This also allowed him to discover that if electrons jump to a lower-energy orbit, they create light or radiation. His discovery significantly changed the preexisting knowledge of atomic orbits and led to more thinking about them. -
After several generations of protests, civil disobedience, and lectures, women gained the right to vote in America!
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Using matrices, Heisenberg formulated an ‘uncertainty principle’ regarding quantum physics which proposed that a particle's position and momentum cannot both be known exactly.
This contributed to thinking about the atom by establishing that atomic fields are not what they were previously known to be. -
Schroedinger thought that matter could be particles and waves, leading him to discover a wave equation to accurately calculate the energy levels of electrons in atoms.
His model assumes that the electron takes on wave-like behaviors, and does not follow defined orbits. -
Eugene Goldstein dies
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Pluto was discovered and named as a planet, a title that would be reclassified in 2006.
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Chadwick discovered the neutron, a particle without any electric charge which exists in the nucleus.
This started the thinking that both protons and neutrons occupy the nucleus, and that they have roughly the same mass. -
Ernest Rutherford
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Japan attacks Pearl Harbor, and the US officially joins WWII.
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JJ Thomson dies
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Robert Millikan dies
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Erwin Schroedinger dies
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Niels Bohr dies
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James Chadwick is born
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Werner Heisenberg dies