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Period: 800 BCE to 350 BCE
Ancient Greece
Evolution of Atomic Theory during the Ancient Greek epoch -
600 BCE
Thales
Thales thought deeply about matter. He decided that, fundamentally, everything must be made of the same thing – much as today we believe that all matter is made of atoms. His idea was that in its most fundamental form, all matter is water. -
430 BCE
Democritus
Democritus named the building blocks of matter atomos, meaning literally “indivisible”. Democritus believed that atoms were uniform, solid, hard, incompressible, and indestructible and that they moved in infinite numbers through empty space until stopped. -
350 BCE
Aristotle
Aristotle believed that matter was continuous and that all things were made of the four elements: Earth, water, wind, and fire. Because he was better known, Aristotle's ideas were followed and Democritus' teachings were forgotten. -
Period: to
Modern Day
Evolution of Atomic Theory dating back to 300 years ago -
Isaac Newton
Isaac Newton contributed to atomic theory through his systematic development of calculus-based object modeling concepts e.g. displacement, velocity, acceleration, and energy, as well as gravity, uniform circular motion, angular momentum, etc. With his work, scientists would soon come to apply said concepts to the electron in orbit about a nucleus. -
John Dalton
Dalton theorized that all matter is comprised of tiny, definite particles called atoms, atoms are indivisible and indestructible, all atoms of a particular element share identical properties, including weight, atoms of different elements contain different masses, and atoms of different elements combine in fixed whole-number ratios when forming compounds. -
Michael Faraday
Michael Faraday, a British physicist, made one of the most significant discoveries that led to the idea that atoms had an electrical component. -
Julius Plucker
Julius Plucker noted that the rays given off by the cathode can be deflected by a magnetic field in a direction which suggests that these cathode rays are negatively charged. This helped in the discovery of the electron -
Dmitri Mendeleev
Mendeleev found that, when all the known chemical elements were arranged in order of increasing atomic weight, the resulting table displayed a recurring pattern, or periodicity, of properties within groups of elements. -
Eugene Goldstein
Eugene Goldstein discovered positive particles by using a tube filled with hydrogen gas. This resulted in the positive particle having a charge equal and opposite to the electron. The positive particle was hence named the proton. -
J J Thompson
J.J. Thomson's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. Thomson proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged "soup." -
Marie Sklodowska Curie
French physicists Pierre and Marie Curie discovered the strongly radioactive elements polonium and radium, which occur naturally in uranium minerals. Marie coined the term radioactivity for the spontaneous emission of ionizing, penetrating rays by certain atoms. -
Max Planck
Planck's work in thermodynamics led to the formulations of his quantum theory. To explain the colours of hot glowing matter, he proposed that energy is radiated in very minute and discrete quantized amounts or packets, rather than in a continuous unbroken wave. -
Hantaro Nagaoka
Nagaoka's Saturnian system suggests that the atom was inherently unstable because, by radiating continuously, the electron would gradually lose energy and spiral into the nucleus. -
Ernest Rutherford
Rutherford's atomic model is the model which described the atom as a tiny, dense, positively charged core called a nucleus, in which nearly all the mass is concentrated, around which the light, negative constituents, called electrons, circulate at some distance, much like planets revolving around the Sun. -
Niels Bohr
Bohr postulated that electrons orbit the nucleus in orbits that have a set size and energy, the lower the energy of the electron and that the lower the orbit. This meant that as electrons fill up the orbitals, they
will fill the lower energy level first. If that energy level is fill (or at capacity), a new energy level will begin. Radiation is when an electron moves from one level to another. -
Louis de Broglie
Louis de Broglie introduced the idea that particles, such as electrons, could be described not only as particles but also as waves. This was substantiated by the way streams of electrons were reflected against crystals and spread through thin metal foils.