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410
Aristotle
Aristotle disbelieved the ancient Greek theory of atoms being different sizes and being regular geometric shapes. He also didn't think that atoms could be in constant motion while invisible. He developed the theory that all matter consisted of four elements: Earth, Air, Water and Fire. -
440
Democritus
440 BCE - A greek philosopher named Democritus predicted that when grinding a rock into a dust that can't get any smaller, there was matter in that rock that was being broken down as well. -
Isaac Newton
Isaac Newton suggested that atoms were held together by attractions/forces.
"Have not the small particles of bodies certain powers, virtues, or forces, by which they act at a distance, not only upon the rays of light for reflecting, refracting, and inflecting them, but also upon one another for producing a great part of the Phenomena of nature?" -Isaac Newton
By this, he means that the smallest particles should be able to affect one another across a distance. -
Robert Boyle
Robert Boyle published 'The Skepticle Chymist', a book where he replaced Aristotle's theory of the four elements, with the modern idea of the elements. -
John Dalton
John Dalton, a scientist and teacher, reconsidered the ancient idea of each different element having a different kind of atom. He suggested that all matter is made up particles called atoms, all atoms of an element have the same size and mass, and that atoms of different elements can be combined to form new substances. -
Antoine Lavoisier
Antoine Lavoisier discovered that water is made of hydrogen and oxygen. He also invented the analytical balance and showed that chemical elements could be combined into different compounds in chemical reactions. He also showed that diamonds and graphite were both forms of carbon, and by burning each you can make carbon dioxide. -
Joseph Louis Proust
Joseph Louis Proust published his law of definite proportions stating that a chemical compound always contains exactly the same amount of elements by mass. -
Joseph Priestly
Joseph Priestly discovered the element oxygen. -
Jon Berzelius
In 1808, John Dalton published a book of his findings of atomic weights and his atomic theory.
In 1814, Jon Berzelius improved this by providing more accurate atomic weights, as well as supplying the weights for newer elements. He also also replaced Dalton’s symbols with the initial letter of each element’s Latin name. -
Michael Faraday
Michael Faraday demonstrated the relationship between the electric field and the magnetic field. He came up with the term electrolysis (the process used in the extraction of reactive metals). -
Dmitri Mendeleev
Dmitri Mendeleev arranged the elements into seven groups with similar properties. He noticed that when the elements were arranged in order of increasing atomic mass, there were similarities in their chemical properties at regular intervals. This became known as the Periodic Law. -
William Crookes
William Crookes discovered cathode rays could travel in straight lines from the cathode; cause glass to fluoresce; impart a negative charge to objects they strike; they're deflected by electric fields and magnets to suggest a negative charge; and cause pinwheels in their path to spin indicating they have mass. He also developed a better vacuum pump that allowed him to produce cathode-ray tubes with less residual gas pressure -
Henri Becquerel
Henri Becquerel discovered radioactivity. -
J. J. Thomson
J. J. Thompson, an english physicist, considered the idea that atoms were made from a combination of particles. He experimented with electric currents in cathode ray tubes. He was able to cause atoms to create streams of negatively charged particles, which were later named electrons.
Thomson also concluded that atoms that have no overall electric charge, must contain positive charges (protons). -
Marie Curie
Marie Curie created the theory of radioactivity. She also discovered two new elements, radium and polonium. -
Harriet Brooks
Harriet Brooks did a series of experiments to determine the nature of the radioactive emissions from thorium. These experiments served as the foundation for the development of nuclear science. -
Max Planck
Max Planck used the idea of quanta (discrete units of energy) to explain hot glowing matter. For example, why a hot iron poker glows distinctly red and white. -
Hantaro Nagaoka
Hantaro Nagaoka preseted a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle, similar to Bohr's atomic model. -
Hans Geiger
In collaboration with Ernest Rutherford, Hans Geiger developed the first version of the 'Geiger Counter' to count the number of alpha particles and other ionising radiation. -
Ernest Rutherford
Ernest Rutherford, a scientist, conducted an experiment in order to test Thomson's model of the stom. In his experiment, he shot positively charged particles at a thin foil of gold. Most of the high speed positive particles went through the foil. However, a few of the particled bounced back from the particles as if it had been deflected by something. Because of this, Rutherford has discovered the nucleus, and that the nucleus contains most of the atom's mass. -
Niels Bohr
Niels Bohr, a danish physicist, along with some other researchers, transformed Rutherford's model into one of the models that are used today. Bohr suggested that electrons surround the nucleus in specific energy levels, called shells. He discovered that electrons jump between these shells by gaining or losing energy. Each shell can only contain a certain amount of electrons. The first shell can hold two, the second and third shells can hold eight, the fourth shell can hold 18, etc. -
Henry Mosely
Henry Mosely was the first one to realize that the atomic number determined the order of the elements. -
Louis de Broglie
Louis de Broglie proposed the idea that electrons could behave as waves under some conditions. -
Werner Heisenberg
Werner Heisenberg came up with the Uncertainty Principle, which states that the exact location and energy of an electron cannot be determined simultaneously. Finding one value (either the energy or the location), means that there will be some uncertainty when finding the other value. -
James Chadwick
James Chadwick discovered the neuron.
