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440 BCE
Plato
Plato discovered that solid forms of matter are composed of indivisible elements. He believed that there were four elements (earth, air, fire, and water). He also said that atoms, contrary to popular belief, were shaped like triangles instead of spheres. He thought that this must be correct because you can put triangles together to make other shapes. While we now know that they really are spherical and not triangular, his discoveries still played a big role in what we know today. -
400 BCE
Democritus
Though technology definitely was not very developed during his time, Democritus still discovered many important things about atoms. He found that atoms are uniform, solid, hard, incompressible, and they move in infinite numbers through empty space until stopped. He also found that differences in atomic shape and size determined the various properties of matter. -
500
The Alchemists
The Alchemists were a group of people (around 500-1700 AD) that sought to change metals to different kinds of metals. Let me explain. Alchemy is the practice of changing "ordinary metals" such as aluminum, tin, and lead to "noble metals" such as gold and silver. The Alchemists used Aristotle's ideas about matter to create experiments. These experiments sought to change metals and ore so they could be more valuable. They believed changing properties of a metal could change the metal itself. -
Robert Boyle
Robert Boyle believed that everything was composed of tiny particles called atoms. During this time he referred to these tiny particles as corpuscles. This idea was known as atomism. He also created Boyles law, stating in simple terms: The volume of gas increases as the pressure around it decreases. -
Antoine Lavoisier
Antoine Lavoisier found out that all matter was composed of atoms, and he found out that atoms were not created or destroyed during chemical reactions. He also grouped the elements. These groups included simple substances, earthly simple substances, metals, and non metals. -
Billiard Ball Model
The Billiard Ball Model was made in 1804 by John Dalton. This model shows how John Dalton describes the atom, (a ball-like structure) though the nucleus and electrons were not known at the time. -
John Dalton
John Dalton made many discoveries about atoms. He discovered that all matter is composed of atoms and that atoms of a given element are identical in size and mass. Also atoms can't be subdivided, created, or destroyed and atoms of different elements can combine in whole number ratios to form chemical compounds. Another discovery was that in a chemical reaction, atoms are rearranged, combined, or destroyed. He also created the billiard ball model which basically states that an atom is round. -
Amadeo Avogadro
Amadeo Avogadro made lots of discoveries about gases. He found that "elementary gas" which includes things like hydrogen, nitrogen, and oxygen, are composed of two atoms. He also found that equal volumes of gas contain equal numbers of molecules. -
Dimitri Mendeleev
Dimitri Mendeleev's law allowed him to create a periodic table built up of 70 elements. He arranged the elements based off their atomic weight. As the creator of the periodic table, he left spaces allowing future scientists to add to it as science is everchanging and he knew it would need updates. -
JJ Thompson
Based off his experiments, JJ Thompson discovered that all atoms contain tiny negatively charged subatomic particles called electrons. These electrons are placed randomly in an area of positive charge. He showed this in his Plum Pudding Model that was released in 1904. -
Pierre and Marie Currie
Most famous for discovering Radium, Pierre and Marie Currie also worked with atoms. Together they discovered two elements that are now on the Periodic table: Radium and Polonium. On her own, Marie deduced that radioactivity doesn't depend on how atoms are arranged into molecules, but rather it originates from the atoms themselves. -
Plum Pudding Model
The Plum pudding model was made by JJ Thompson in 1904. This model depicts how electrons (as negatively charged particles) are embedded in a sea of positive charge. The model was named the Plum Pudding Model because plum pudding is served round like an atom and the fruit is randomly placed into the pudding just like how the electrons are randomly placed in the positive charged sphere. -
Albert Einstein
Albert Einstein's work was revolutionary to science in many ways, including his work with atoms! Einstein mathematically proved the existence of atoms, and mathematically predicted the size of both atoms and molecules. As you can see, he revolutionized all science through the use of statistics and probability. He also found out that liquid was made of molecules and that molecules are always in random ceaseless motion. -
Robert Millikan
Robert Millikan proved that electrons have a fixed measurable charge that does not vary, and discovered the charge of a single electron using the famous oil drop experiment. In this experiment, tiny oil droplets are suspended in an electric field, and the motion of these droplets are observed, determining the charge of electrons. Through his discoveries, he also allowed future scientists to calculate the mass of a single electron. His discoveries were made in 1910 but published in 1913. -
Ernest Rutherford
Ernest Rutherford described the atom as having a tiny dense and positively charged core called the nucleus. He also stated that the mass of an atom is concentrated in its nucleus. Based off this information, he created the Rutherford Planetary Model also known as the Rutherford Nuclear Atom, or the Rutherford Atomic Model. -
Niels Bohr
Niels Bohr discovered that electrons moved around a nucleus but only in prescribed orbits. This showed in his model, the Solar System Model. Using Quantum Theory, Bohr proposed a theory for the hydrogen atom, stating that some physical properties only take discrete values. (Discrete values are basically whole numbers instead of fractions) -
Solar System Model
Also known as the Bohr Model or the Planetary Model, the Solar System Model was made in 1913 by Niels Bohr. According to the Solar System Model, electrons encircle the nucleus of the atom in specific allowable paths called orbits. This is just like planets (the electrons) orbiting the sun (the nucleus containing protons and neutrons). When an electron is in one of these orbits, its energy is fixed. -
Henry G.J Moseley
Henry G.J Mosely discovered that each element is defined by its atomic number. An atomic number represents the number of protons in an element's nucleus. Because of this he found that the square root of the frequency of the emitted x-ray is proportional to its atomic number. -
Electron Cloud Model
The Electron Cloud Model was made by Erwin Schrödinger in 1962. An electron cloud is the area around atoms in the nucleolus where electrons are most likely to be formed. Therefor the Electron Cloud Model is a mathematical model that helps predict where electrons will be at a given time. -
Erwin Schrödinger
Similar to Albert Einstein, Erwin Schrödinger mainly used math to make discoveries. For example, Schrödinger formulated an equation that accurately calculates energy levels of electrons in atoms. He also used mathematical models to create an equation used to predict the likelihood of finding an electron in orbit. This model was called the Electron Cloud Model. -
James Chadwick
James Chadwick discovered the neutron in 1932. A neutron is a subatomic particle found in the nucleus of an atom that has no electric charge; it's neutral.