Beginning of Chemistry

Main Characters in the Development of the Atom

Democritus

J.J. Thomson

Lord Ernest Rutherford

Robert Millikan

Niels Bohr

James Chadwick

Vital to the Development

Democritus is associated with the first atomic theory; to him atoms were completely solid, homogeneous, indestructible objects.

Joseph John Thomson discovered the electron in 1897 by experimenting with cathode rays. He also came up with the "plum-pudding" model of the atom, which suggested a solid atom with positively and negatively charged particles evenly distributed throughout the mass of the atom.

Ernest Rutherford discovered that most of the atom is made up of "empty space." In 1909 he conducted the "gold foil" experiment, from which he found that most of the atom's mass was concentrated in a minute nucleus. He concluded that the positively charged nucleus was surrounded by a great deal of "empty space" through which the electrons moved.

Robert Millikan found the mass of the electron to be 9.11x10^-28g by combining the results from his "oil-drop" experiment, which allowed him to measure the charge on an electron, with those of Thomson's.

Niels Bohr added the idea of fixed orbits, or energy levels for the electron traveling around the nucleus, to Rutherford's atomic model. This model allowed for the idea that electrons can become "excited" and move to higher energy levels for brief periods of time.

James Chadwick is known as the discoverer of the neutron. He found these uncharged particles with essentially the same mass as the proton.

What Made them Different

Each scientist was different mainly because of their approach on the atom. They each used different experiments and came out with different results. Even though they were each studying the atom, they each went above and beyond what the one before them studied. They also studied and discovered different parts of the atom such as the proton, neutron, and electron. All in all, each scientist helped with discovering the atom.

Time Period

If we look at the time line of the development of the atom, we notice that as we get closer to modern times, more and more discoveries are made. This is all due to advancements in technology. Also, the advancements in technology allowed the scientists to do further research on past experiments to answer some unanswered questions. This led to clarification and better understanding of the atom. Therefore we may think of the more modern scientists as better scientists but honestly, they had more to work with.

Atomic Theory

After hundreds of years of research, no one has yet seen a single atom. Some of the very best microscopes have produced images of groups of atoms, but no actual picture of an atom yet exists. Therefore, we can't be completely certain of the existence of atoms and of the models they have created for scientists. But. the models of the atom, like other scientific models, can be tested by experimentation. Those models that pass the test of experimentation survive, while those that do not are abandoned. The model of atoms that scientists use today have survived and have been modified by untold numbers of experiments and will be subjected to other such tests in the future. Since we have further testing to do, we can not call it a law yet.

Structure of an Atom

It's important to understand the structure of an atom because atoms are the basic building blocks of matter. They form the molecules that are involved in the processes of living systems. Through the reactions of different atoms, organisms exist. By developing an understanding of the atom and its components, we is develop an understanding of life.