Test Question 1A

-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. 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.
1) The first atomic theory was made by Democritus in 460 B.C. He asked this question: If you break a piece of matter in half, and then break it in half again, how many breaks will you have to make before you can break it no further? Democritus thought that it ended at some point, a smallest possible bit of matter. He called these basic matter particles, atoms. These atoms were all composed of the same primary matter with the only differences between them being their size, shape and weight. The differences in these characteristics explained the differences in the properties of the matter around us.
2) Couloumb (1780's), France - formulated the Coulomb's law, which states that that the force between two electrical charges is proportional to the product of the charges and inversely proportional to the square of the distance between them, one of the main forces involved in atomic reactions.
3) John Dalton helped to explain the laws of chemical reactivity; He performed experiments with various chemicals that showed that matter, indeed, seem to consist of elementary lumpy particles (atoms). Although he did not know about their structure, he knew that the evidence pointed to something fundamental. Dalton's theory also helped further the concept of atomic weights. By assuming that nature would be a simple as possible, Dalton assumed that the elements preferred to combine in one to one ratios, and was therefore able to tabulate a set of relative weights.
Dalton's theory can be summarized as follows:
-Matter is composed of small particles called atoms.
-All atoms of an element are identical, but are different from those of any other element.
-During chemical reactions, atoms are neither created nor destroyed, but are simply rearranged.
-Atoms always combine in whole number multiples of each other.
4) In 1897, the English physicist J.J. Thomson discovered the electron and proposed a model for the structure of the atom. Thomson knew that electrons had a negative charge and thought that matter must have a positive charge.
5) Robert Millikan (1908), USA - found out the electric charge of the electron. He determined the unit charge of the electron in 1909 with his oil drop experiment at the University of Chicago. Thus allowing for the calculation of the mass of the electron and the positively charged atoms. e = 1.60 x 10^-19 coulombs
6) Ernest Rutherford-1909-1911---British physicist, who became a Nobel laureate for his pioneering work in nuclear physics and for his theory of the structure of the atom. He used the results of his gold-foil experiment to state that all the mass of an atom were in a small positively-charged ball at the center of the atom.
7) Neils Bohr-1913---Bohr made numerous contributions to our understanding of atomic structure and quantum mechanics. He stated that the electrons moved around the nucleus in successively large orbits. He also presented the Bohr atomic model which stated that atoms absorb or emit radiation only when the electrons abruptly jump between allowed, or stationary, states.
Bohr’s Rules:
-Electrons can orbit only at certain allowed distances from the nucleus.
-Atoms radiate energy when an electron jumps from a higher-energy orbit to a lower-energy orbit. Also, an atom absorbs energy when an electron gets boosted from a low-energy orbit to a high-energy orbit.
8) In 1931 Chadwick discovered the neutrally-charged neutron. He found it to measure slightly heavier than the proton with a mass of 1840 electrons and with no charge (neutral). The proton-neutron together, received the name, "nucleon.”