Question 1 by Charlotte Quaas

Democritus- stated that the material cause of all things that exist is the coming together of atoms and void. Atoms can never be destroyed and have many different shapes and can cluster together to form things that we can see, touch, taste, smell, etc. Different shapes and arrangements of atoms as well as positions can produce different things as well.

John Dalton- proposed the Atomic Theory in 1803. This theory stated that: all matter was composed of small indivisible particles called atoms, atoms of given elements possess unique characteristics and weight, and there are 3 types of atoms; simple, compound, and complex.

Dmitiri Mendeleev- is known for arranging the 63 known elements into a Periodic Table based on atomic mass. His first periodic table was created on the basis of organizing the elements in ascending order of atomic weight and grouping them by similarity of properties. Mendeleev gave space and variety from strict atomic weight order, which left space for new elements to be discovered. The original table has been modified and corrected several times over the years especially by Mosley. The non modified Periodic Table accommodated the discovery of isotopes, rare gases, etc.

J.J. Thompson- he was experimenting with electricity inside empty glass tubes as was investigating a very old puzzle known as "cathode rays". These experiments gave him the idea to make a bold proposal: that these mysterious rays are particles much smaller than atoms and also are parts of an atom these were called "corpuscles". This proposal turned out to be correct, the rays were made up of electrons.

Earnest Rutherford- whose work constituted a notable land mark in the history of the atom. How he did this was he developed Bacquerel's discovery of Radioactivity into proof that atoms of heavier elements actually disintegrate into different forms of radiation. He is also famous for using particles as atomic bullets and shot them at a thin piece of gold foil. He stated that the nucleus was very dense, small and positively charged. He assumed electrons were located outside of the nucleus.

H.G.J. Moseley- he studied the x-ray spectra of elements and created a truly scientific basis of the Periodic Table by arranging chemical elements in the order of their atomic numbers. During this time Rutherford and his team ( Niels Bohr, Moseley, and others) developed the first coherent theory of the structure of the atom. Their work demonstrated that each element has its own "finger print"; no element was the same. They discovered this by using spectroscopy which they did to nearly all of the elements.

Niels Bohr- he began to work on the problem of the atomic structure. Rutherford had recently said that the atom had a miniature nucleus surrounded by a cloud of electrons. There were some problems with this like: the electrons orbiting the nucleus would lose energy until the spiraled down into the center of the nucleus which would further collapse the atom. Bohr added the new idea of quanta to the model. If the atom absorbed energy the electron would move um a level from the nucleus, and vice versa. This model was a huge leap forward in making a theory fit the evidence gathered over the years.

Schrodinger- his great discovery was his wave equation, which came as a result of his dissatisfaction with the quantum condition in Bohr's orbit theory. he believed that the atomic spectra should be determined by some kind of problem. Schrodinger viewed electrons as continuous clouds which introduced wave mechanics as a mathematical model of the atom.