Atomic structure Bohr-Rutherford model

In the early part of the twentieth century, then, a simple model of atomic structure became accepted, now known as the Rutherford nuclear model of the atom, or, subsequently, the Bohr-Rutherford model. This supposed that most of the mass of the atom is concentrated in the nucleus, which consists of protons (positively charged particles) and neutrons (electrically neutral particles, of approximately the same mass). The number of protons in the nucleus is called the atomic number, which essentially defines the nature of... 

Although there is no detector that allows us to see the inside of an atom, scientists infer its structure from the properties of its components. Rutherford s model shows electrons orbiting the nucleus like planets around the sun. In Bohr s model the electrons travel around the nucleus in specific energy levels. According to the current model, electron orbitals do not have sharp boundaries and the electrons are portrayed as a cloud. 

The dual wave-particle model of light accounted for several previously unexplainable phenomena, but scientists still did not understand the relationships among atomic structure, electrons, and atomic emission spectra. Recall that hydrogens atomic emission spectrum is discontinuous that is, it is made up of only certain frequencies of light. Why are the atomic emission spectra of elements discontinuous rather than continuous Niels Bohr, a Danish physicist working in Rutherford s laboratory in 1913, proposed a quantum model for the hydrogen atom that seemed to answer this question. Bohr s model also correctly predicted the frequencies of the lines in hydrogens atomic emission spectrum. 

Models are often used to describe the structure of atoms, the configuration of their subatomic particles, and their interactive behavior. Of the several models for atomic structure, including those of J.J. Thomson in 1907 and Lord Rutherford in 1911, the Bohr model, proposed in 1913, is used here to illustrate atomic principles.Two assumptions made by Bohr are critical to using his model (1) Stationary energy states exist such that an atom in one of these states is stable and the atom in this state is populated for a finite period of time and (2) the emission or absorption of radiation from an atom is exactly equal to the difference between two of the discreet energy states. 

One example that is often used in chemistry classrooms may illustrate this. In the core of learning about the nature of science is learning about scientific models. Among other characteristics it is important to understand that models in science are developed by scientists, these models are never fully true or false, and can be changed or replaced in the light of new evidence. Different historical models of atomic structure are a good example to reflect about the nature of models in chemistry education. Models of Democritus, Dalton, Thomson, Rutherford and Bohr can be compared in the chemistry classroom, e.g. in a drama play (see Chapter 7). Students can start reflecting about the predictive potential and limitations of the different models. But students can also learn about the time in which the models were developed and about the scientists behind them. Other examples are different models of oxidation and reduction or acid-base chemistry. 

The first steps toward the understanding of the nature of the chemical bond could not be taken until the composition and structure of atoms had been elucidated. The model of the atom that emerged from the early work of Thomson, Rutherford, Moseley, and Bohr was of... 

An estimate of die size of the proton and an understanding of the structure of the hydrogen atom resulted from two major developments in atomic physics the Rudierford scattering experiment (1911) and the Bohr model of die atom (1913). Rutherford showed that the nucleus is vanishingly small compared to the size of an atom. The radius of a proton is on the order of 10-13 centimeter as compared with atomic radii of 10-3 centimeter, Thus, the size of a hydrogen atom is determined by the radius of the electron orbits, but the mass is essentially that of the proton,... 

The spectrum emitted by an atom presumably is related to the structure of the atom. Until 1913, attempts to relate the spectrum to a definite atomic model were unsuccessful. By 1913 it was known that the atom had a positively charged nucleus, but the nuclear model of Rutherford was unstable according to classical electromagnetic theory. This Gordian knot was cut by Niels Bohr in 1913. 

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