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Aristotle's Theory- table
Aristotle's Theory was the idea for the four basic elements: fire, water, earth, and air. Earth is cold and dry; corresponds to the modern idea of a solid. Water is cold and wet; this corresponds to the modern idea of a liquid. Fire is hot and dry; this corresponds to the modern idea of heat. Air is hot and wet; this corresponds to the modern idea of a gas. There is one more element that he came up with and it is Aether. That is the devine substance that makes up the heavenly spheres. -
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Democritus- theory
An ancient Greek per-Socratic philosopher, discovered that all atoms are indivisible to see with eyes. The atomic hypothesis was that everything is made of atoms and that between atoms is empty space. He also proposed the earliest views on the shape and connectivity of atoms. -
Robert Boyle- theory
He measured relationships between volume and pressure of gasses. From his expiraments he concluded that gasses are made up of tiny particles that group together to make different substances. -
John Dalton- theory
His theory was presented in the new systems of Chemical property which stated that all matter was composed of small indivisible particles termed atoms, atoms of a given element that had unique characteristics, weight, and three types of atoms. -
Johann Dobereiner, triad system- table
In the year 1829, Johann Wolfgang Dobereiner, a German scientist, was the first to classify elements into groups based on John Dalton's assertions. He grouped the elements with similar chemical properties into clusters of three called 'Triads'. The distinctive feature of a triad was the atomic mass of the middle element. -
Dmitri Mendeleev- First Periodic Table of the Elements- table
Mendeleev published a table of elements arranged in order of increasing atomic mass. He left gaps for elements not yet discovered for example Scandium, Gallium and Germanium, and predicted their properties. He also corrected the atomic masses of Beryllium, Indium and Uranium. -
Lothar Meyer- A Different Periodic Table- table
Meyer published his own table of elements at the same time as Mendeleev. It was also organised by increasing atomic mass. However Mendeleev is known as the "father of the periodic table", and Meyer is not; even though they both arranged the elements by increasing atomic mass and left gaps for undiscovered elements. The reason taht Mendeleev is credited is because he predicted correctly the characteristics of these undiscovered elements. -
Julius Lothar von Meyer, orgainised by atomic mass- table
Meyer is best known for arraigning them in the order of their atomic weights they fall into groups in which similar chemical and physical properties are repeated at periodic intervals; and in particular he showed that if the atomic weights are plotted as ordinates and the atomic volumes as abscissae, the curve obtained presents a series of maxima and minima, the most electro-positive elements appearing at the peaks of the curve in the order of their atomic weight. -
Electron- theory
J.J Thomson discovery of the electron came out of curiosity when he was conducting an experiment which involved a ray of electricity being passed through a vacuum tube. A mysterious light would appear because of this and it was Thomson who discovered that it would bend slightly towards a positively charged plate. Thus the negatively charged electron was discovered the charged plate and the negative charged electron was also discovered. -
Plum pudding model- theory
Discovered by J. J. Thomson, discovered the electron in 1897. It was proposed in 1904 before the discovery of the atomic nucleus in order to add the electron to the atomic model. It was called the plum pudding model because of the negatively charged plums surrounded by positively charged pudding. -
Rutherford atomic model- theory
Made by Rutherford in 1911. It showed nucleus and the electrons orbiting the nucleus. It was also a major event in the atomic theory. -
Gold foil experiment- theory
Gold foil experiment- The famous gold foil experiment was done by Rutherford. This experiment involved the firing of radioactive particles through a gold thin metal foils and detecting them using screens coated with zinc sulfide. Rutherford found that although most of particles passed straight through the foil about 1 in 8000 were deflected leading him to his theory that most of the atom was made up of 'empty space'. -
Henry Moseley- Atomic Number vs Atomic Mass- table
Moseleyn rearranged the order of the elements from increasing atomic mass to increasing atomic number. In addition, Moseley showed that there were gaps in the atomic number sequence at numbers 43, 61, 72, and 75. These spaces are now known, respectively, to be the places of the radioactive synthetic elements technetium and promethium, and also the last two quite rare naturally-occurring stable elements hafnium and rhenium. -
Bohr's model- theory
Bohr proposed that the electrons orbited the nucleus much the way that planets do to the sun. He also stated that the nucleus of an atom is much tinier than once thought and that the electrons themselves are father apart from the nucleus. Along with showing that there were different electrons clouds in which the electrons were found. -
Glenn T. Seaborg, discovery of elements and rearrangment of element- table
After co-discovering 10 new elements, in 1944 he moved 14 elements out of the main body of the periodic table to their current location below the Lanthanide series. These became knownas the Actinide series. Seaborg was the principal or co-discoverer of ten elements: plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium,nobelium and element 106, which was named seaborgium in his honor while he was still living. -
First Atomic Bomb dropped- theory
They made this bomb by spiting atoms. To highly react with each other to make a big explosion that flattened Hiroshima at the end of World War Two. His bomb was so powerful that when it hit the ground it killed 90,000-166,000 Hiroshima people. -
Quantum Mechanical Model-theory
The current day model of an atom is based on a theory of quantum mechanics. Each electron is thought of as a cloud, of negative charge, instead of one tiny negative particle. It is beleived in this model that electrons "occupy" all of the space in an atom at different levels or rings. An atom consists of energy levels, neutrons, and protons.
