C.6A: Atomic Theory Atomic Structure and Nuclear Chemistry

KEY CONCEPTS Texas Essential Knowledge and Skills Statement C.6: �The student knows and understands the historical development of atomic theory. The student is expected to:

(A)  understand the experimental design and conclusions used in the development of modern atomic theory, including Dalton's Postulates, Thomson's discovery of electron properties, Rutherford's nuclear atom, and Bohr's nuclear atom; (i)   understand the experimental design used in the development of modern atomic theory,

including Dalton's Postulates (ii)  understand the conclusions used in the development of modern atomic theory, including

Dalton's Postulates (iii)  understand the experimental design used in the development of modern atomic theory,

including Thomson's discovery of electron properties (iv)  understand the conclusions used in the development of modern atomic theory, including

Thomson's discovery of electron properties (v)   understand the experimental design used in the development of modern atomic theory,

including Rutherford's nuclear atom (vi)  understand the conclusions used in the development of modern atomic theory, including

Rutherford's nuclear atom (vii)  understand the experimental design used in the development of modern atomic theory,

including Bohr's nuclear atom (viii) understand the conclusions used in the development of modern atomic theory, including

Bohr's nuclear atom�

Key Concept #1: �The concepts of the atom and the nature of matter originated with Greek philosophers more than 2,000 years ago. These ideas, though not scientifically tested, formed the basis for later scientists to build upon and develop modern atomic theory. �

Key Concept #2: �John Dalton extensively investigated the nature of gases in the early 1800s in order to gain a better understanding of the Laws of Conservation of Mass and of multiple proportions. His resulting five postulates of atomic theory helped to define the structure and nature of the atom. The scientific community accepted his postulates due to his sound experimental evidence. �

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C.6A: Atomic Theory Atomic Structure and Nuclear Chemistry

KEY CONCEPTS Key Concept #3: �J.J. Thomson experimented with particles known as cathode rays. In the late 1800s he discovered that these rays were actually negatively charged particles with a charge of 1-, and that they were much smaller than atoms. He conducted further experiments to investigate the relationship between electric charge and matter. Thomson developed the “plum pudding model,” in which electrons were embedded in a positively charged sphere.

Key Concept #4: Ernest Rutherford developed the nuclear model of the atom in the early 1900s. He came to his conclusion after analyzing the results of his experiment, known as the Rutherford scattering experiment, in which he found that atoms contained an extremely small, dense, and positively charged nucleus, and that the area around the nucleus was mostly empty space with a few negative electrons.

Key Concept #5: Niels Bohr refined the findings of Rutherford in the early 1900s. Bohr used spectral light emissions to conclude that electrons had specific energy levels, known as quantized energy levels. His atomic model consisted of spherical shells of electrons on various states surrounding the positively charged nucleus.

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FUNDAMENTAL QUESTIONS

•  Where did the concept of the atom originate, and what were the limitations of this initial theory?

•  How did Dalton’s Postulates contribute to the development of modern atomic theory?

•  What was J.J. Thomson’s contribution to the development of the model of the atom?

•  What did Ernest Rutherford discover that significantly changed the model of the atom?

•  How did Niels Bohr’s research further develop the Rutherford model of the atom?

©2012RiceUniversity‐AllRightsReserved

C.6A: Atomic Theory Atomic Structure and Nuclear Chemistry