Question 1B

Examine the history of the development of the atom. We have already discussed the
major players in the development of the atom. Pick out at least 8 major players who
helped aid in the development of the concept of the atom. Then explain each
experiment in a concise explanation. Then explain how each one aided in the
development of the next or how their concept assisted in the further development of the current quantum model of the atom.

JJ Thomson- Used Cathode rays to hypothesize that there were smaller particles contained inside of the atom. JJ was right and the particles inside are called electrons. These are negatively charged particles and are fundamental parts of the atom. The cathode rays are currents of electricity inside of glass tubes. Thomson finding electrons helped with the quantum model because it shows that there are electrons in the outer parts.

Democritus- Looked at the world with a mechanistic view, and would only give mechanistic views. He came up with a theory that everything is made up of atoms and that they are indestructible and that they are always in motion, leading up to how Dalton looked at history.

Chadwick- used alpha particles to find the neutrons in an atom. Rutherford had been working with Chadwick and thought that there was a neutral element of the atom because the atomic mass did not add up when compared the whole atom and the things inside. Chadwick used a different type of experiment to track particle radiation that showed that the neutrons were .01 percent bigger than a proton and could account for the mass. Soon after they started using neutron bombarding to split up an atom, the neutron helped with providing how the atomic mass could be equal. This helped show where to put neutrons providing that they did not bond with any other particle.

Dalton-He came up with Dalton’s atomic theory. This theory was partly right by him saying that atoms of the same element are alike in weight and other properties and those different atoms are different in weight and other properties. He was also right about compounds forming by the union or separation of definite numbers of atoms. The incorrect part was that all matter is composed of very small indivisible particles called atoms. Also, those atoms do not divide in chemical reactions; only whole atoms unite with other atoms, this was incorrect. Dalton helped with our quantum model by providing that every atom is different.

Rutherford- Discovered that atoms of the heavier elements disintegrate into radiation. Rutherford also used the gold foil experiment to find that there were protons in the atom. This experiment used a particle emitter and shot it through a slit in the detection screen at a piece of gold. While most of the particle went through the gold some came back at a very small amount. Rutherford concluded these were protons. Rutherford helped in the quantum model by showing that there is positive charged particles, which led to other people drawing the atom and leading up to the quantum atom.

Moseley- Put elements in the periodic table by atomic number because it proved to make the elements fit better. He even showed that nickel and cobalt had the wrong atomic masses and that with his calculating of the atomic numbers it correctly ordered the periodic table. Mendeleev also knew there were missing elements in the periodic table. Moseley provided the used of the PT to many people, even though there are some unknown elements, this provided the most accurate calculations and helped with the quantum by telling the atomic number which shows how many electrons there are.

Bohr- In 1913, Bohr published a theory about the structure of the atom based on an earlier theory of Rutherford's. Rutherford had shown that the atom consisted of a positively charged nucleus, with negatively charged electrons in orbit around it. Bohr expanded upon this theory by proposing that electrons travel only in certain successively larger orbits. He suggested that the outer orbits could hold more electrons than the inner ones, and that these outer orbits determine the atom's chemical properties.

Mendeleev- organized the periodic table by the elements atomic weight and properties. Predicted where there was a gap in the periodic table that the element would be found and that it would be put in to the proper place without affecting the order of the table. Mendeleev was right and three elements were found in his lifetime. These elements are lifetime gallium, scandium, and germanium. This helped with understanding the universe and how things are in the world.