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460 BCE
The birth of Democritus
Democritus didn't work with anyone to prove his ideas. Back then, no one believed him. -
Period: 460 BCE to 370 BCE
The life of Democritus and his accomplishments
Democritus (c.460 BC - 370 BC) first believed in the atom's importance. He reasoned that any piece of matter could be broken in half constantly until it couldn't be broken apart any further, resulting in the atom. However, no one in his time accepted this theory. Aristotle's theory was most accepted back then and for a long time after that. However, in 1803 (over two millenniums and two centuries later), John Dalton proposed his atomic theory similar to Democritus's, making his theory accepted. -
400 BCE
Democritus proposes the model of the atom
Democritus developed the idea of the atom: -
384 BCE
Birth of Aristotle and a picture of him
The following is what Aristotle looked like: -
Period: 384 BCE to 322 BCE
Life of Aristotle
Aristotle was born in c.384 BC and died in c.322 BC due to stomach problems. He thought that the world was built using the basic 4 elements (fire, air, water, earth). He also developed the scientific method, which is used to this date often. His ideas contradict Democritus's ideas of the atom, resulting in Aristotle's ideas proving to be more believable back then. All the way until the 18th or 19th century, everyone believed Aristotle, until his ideas about elements were proven wrong. -
355 BCE
Aristotle proposes his theory (day unknown - 335 BC - when he started teaching)
The following diagram shows what Aristotle believed in: (it turned out to be incorrect) -
Lavoisier's birth
The following is a picture of him: -
Period: to
The life of Antoine Lavoisier
Lavoisier created the idea of conservation of matter, distinguished between elements and compounds, and started discussion on atoms and what they actually look like. Conservation of matter is essential to modern chemistry, which made him an excellent scientist. Matter was changed and reformed, not created or destroyed, according to this law. He didn’t really do work with atoms, but he did a lot of work with different elements, including experimenting with mercury and oxygen, separating them. -
The birth of Dalton
This is a picture of the scientist: -
Period: to
The Life of John Dalton
John Dalton proposed an atomic theory. He had experimented with different chemicals that showed that matter contain various particles called atoms. Elements were made up of atoms. Elements were also pure (all atoms of an element are pure). A compound is a pure substance as elements are bonded together. He also believed that all elements have different masses. Basically, everything is made up of atoms. He also thought that chemical reactions rearranged atoms. Thanks to Dalton, we have the atom. -
Lavoisier proposes his law of conservation of matter
The following is a picture of Lavoisier's law of conservation of matter: (date proposed unknown)
Lavoisier did a lot of his work with his wife. -
John Dalton proposes his atomic theory
This is a picture of John's atom: (it's similar to Democritus) -
Period: to
The life of Henri Becquerel
Henri Becquerel discovered radioactivity, but sadly he never knew it. He was in the middle of an experiment, trying to experiment with crystals and a photographic plate. In the experiment, he shined a crystal in sunlight that contained uranium. After he exposed it to light, he placed it on black paper, creating an image. For two days, he couldn’t continue his work due to the weather, but when he took the paper out, to his surprise the image was clear and strong. He had discovered radioactivity. -
The birth of J. J. Thomson
The following is a picture of the scientist: -
Period: to
The life of J.J. Thomson
J.J Thomson discovered the electron. He was studying cathode rays. He was doing an experiment involving the rays and let them transfer thorough air without a vacuum. He also deflected the ray using differently charged fields, one positive and one negative. Glowing materials bent on the positive plate. He discovered that these were sub-atomic particles, smaller than an atom. He had discovered the electron. His legacy was the discovery of the electron, changing the whole world in a very new way. -
The birth of Max Planck
The following is a picture of the scientist:
Max Planck worked with Einstein and created a new theory, but he didn't work with other scientists listed here. -
Period: to
The accomplishments and life of Max Planck
Max Planck (born Apr. 23, 1858) originated the quantum theory and several constants. He discovered the theory along with another equation about black body radiation. He wanted to combine formulas to discover the answer to a specific question. It’s called Planck’s radiation law (he also discovered Planck’s constant, h). The quantum theory (quantum is a measure of energy in physics) changed what we now think about atoms and radiation. His ideas led him to obtain the Nobel Prize in physics in 1918. -
Period: to
The lifetime of the Curies (Marie and Pierre Curie - the timespan is Marie Curie's life)
Marie Curie was a chemist that discovered two different elements, radium and polonium, with the help of her husband Pierre Curie. Slightly before her time, Henri Becquerel had discovered radiation using uranium and the sun. She based her work off that, resulting in her discovering ideas like radioactivity could be measured. Her legacy was very important to current important ideas, including radioactive dating, isotopes, medical use of radioactive isotopes, and support of Dalton’s atomic theory. -
Period: to
The life and accomplishments of Robert Millikan
Robert Millikan was a chemist that wanted to continue work in the electron. He did an experiment to discover the incremental charge of an electron. His results indicated that the charge was just one specific value. He also found out the charge to mass ratio. The formed electron clouds could be measured. The denser the clouds, the easier it was to find an electron. He helped scientists like Einstein and Niels Bohr and provided them with helpful info. He also discovered the weight of the electron. -
The birth of Ernest Rutherford
The following is a picture of the scientist: -
Period: to
The life of Ernest Rutherford and his discoveries
Ernest Rutherford (born Aug. 30, 1871) was the scientist that discovered the nucleus of an atom, proving J.J. Thomson’s plum pudding model incorrect. He used an extremely thin sheet of gold and positively charged helium atom particles to conduct his gold foil experiment. The results of the experiment show that there was a small, positively charged area in the middle of an atom that was most of the mass of the atom. In J.J. Thomson’s plum pudding model, the particles were spread out in the atom. -
The birth of Niels Bohr
The following picture is a picture of the scientist: -
Period: to
The life and accomplishments of Niels Bohr
Niels Bohr stated that electrons moved around the nucleus at fixed rates and that atoms take in or emit radiation at limited times. The chemical properties of the atom were based on the number of electrons it had. This theory also explained how atoms emitted light in fixed wavelengths. He explained what happens in an atom. In his models, there were layers of electrons and electron shells. Each layer had a limit to the number of electrons possible and there was no limit on the number of layers. -
The birth of Erwin Shrodinger
The following is what he looked like: -
Period: to
The life of Erwin Shrodinger
Erwin Shrodinger was a physicist that improved quantum mechanics, He used mathematical equations to better describe the position of an electron. The model that he made is based on odds of how likely the electron will arrive at a specific spot. Basically, the model is an electron cloud surrounding the nucleus of the atom. He also worked with mathematical models involving “wave mechanics” and atoms. The new model that he proposed was based off of Bohr’s model, taking it one step further to today. -
Period: to
The short life of Henry Moseley
Henry Moseley (born Nov. 23, 1887) was a physicist who discovered the atomic number for various elements using x-rays. Before his time, the periodic table was full of assumption and guesses. As a result of his ideas, scientists over the next 30 years filled in gaps in the Periodic Table. He decided to investigate after he started a collaboration with Niels Bohr. To actually do the x-rays, he consulted the grandson of Charles Darwin, C.S. Darwin, and changed the periodic table to the current one. -
The birth of James Chadwick
The following is a picture of him: -
Period: to
The life and accomplishments of James Chadwick
James Chadwick was the scientist that proved the existence of neutrons in atoms. He had gone through many failed experiments while trying to prove the existence of particles with a neutral charge. He was using wax and gamma rays to determine how to separate protons from neutrons. He had no idea that it was a new particle, not a proton + an electron. As a result from his findings, he was awarded the Nobel Prize in Physics in 1935. It also led to the first atomic bomb and the end to World War II. -
Henri Becquerel's atom picture (radioactivity)
The following is a picture of radioactivity: -
The Curies propose radioactivity
The Curies propose their discovery on this date. -
Max Planck proposes the quantom theory
The following is an image of the quantum theory: (day and month unknown) -
Period: to
The life of Werner Heisenberg and his accomplishments
Werner Heisenberg worked with electrons and showed that the electron did not move in a specified, neat path. He used math to help determine the position of atoms. The quantum theory was used to determine the exact path of the electrons. Not everything about electrons could be seen. As a result, Heisenberg used what he could, creating an unfamiliar mathematical statement in the 1920s. His mentor thought it made sense, so the paper was published, leading to a new breakthrough in quantum mechanics. -
J.J.Thomsonn proposes his atomic theory
J.J. Thomson proposed his atomic theory in this month and year. Here's a picture of the atom: -
Rutherford discoveres that J.J. Thomson's ideas were wrong
The following is the result of the gold foil experiment by Rutherford: -
Henry Moseley uses radioactivity to discover the atom
Henry Moseley used radioactivity and x-rays to determine atomic numbers for elements: -
The discovery Niels Bohr made
He discovered the path of the electron: -
The Oil drop experiment: Robert Millikan
The picture is a description of the experiment: -
Erwin Shrodinger creates the modern quantom model
The following is a picture of it: -
Werner Heisenberg proposes his theory
He thought that the electron cloud existed. (back in hs day it would be 5 years befor the existenc of neutons would be proved.) -
James Chadwick discovers the neutron and proves Ruterford correct
The folloig year is whe Chadwick povd the existence of the neutron:
