Sunday, October 24, 2010
Question 1B
Niels Bohr- A model of the atom, first described by Niels Bohr, that explains the emission and absorption of radiation as transitions between stationary electronic states in which the electron orbits the nucleus at a definite distance. The Bohr model violates the Heisenberg uncertainty principle, since it postulates definite paths and momenta for electrons as they move around the nucleus. Modern theories usually use atomic orbitals to describe the behavior of electrons in atoms.
Ernest Rutherford- Ernest Rutherford explains his atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons. This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space. Rutherford came to this conclusion following the results of his famous gold foil experiment. This experiment involved the firing of radioactive particles through minutely thin metal foils (mostly gold) and detecting them using screens coated with zinc sulfide (a scintillator). Rutherford found that although the vast majority of particles passed straight through the foil approximately 1 in 8000 were deflected leading him to his theory that most of the atom was made up of 'empty space'. His model didn't make any headway in the explanation of the electrons but just kinda helped in the understanding of the past and present atomic structures.
William Crookes- This fascinating scientist discovered the phenomenon upon which depends the action of the well-known little instrument, the Crookes radiometer, in which a system of vanes, each blackened on one side and polished on the other, is set in rotation when exposed to radiant energy. He did not, however, provide the true explanation of this apparent attraction and repulsion resulting from radiation. Of more fundamental importance were his researches on the passage of the electrical discharge through rarefied gases. He found that as the attenuation of the gas was made greater the dark space round the negative electrode extended, while rays, now known as cathode rays, proceed from the electrode. He investigated the properties of the rays, showing that they travel in straight lines, cause phosphorescence in objects upon which they impinge, and by their impact produce great heat. He believed that he had discovered a fourth state of matter, which he called "radiant matter". But his theoretical views on the nature of "radiant matter" proved to be mistaken. He believed the rays to consist of streams of particles of ordinary molecular magnitude. It remained for J. J. Thomson to discover their subatomic nature, and to prove that cathode rays consist of streams of negative electrons, that is, of negatively electrified particles whose mass is only 1/1,800 that of the atom of hydrogen.
J.J. Thompson-Thomson's work suggested that the atom was not an "indivisible" particle as John Dalton had suggested but, a jigsaw puzzle made of smaller pieces.
Thomson's notion of the electron came from his work with a nineteenth century scientific curiosity: the cathode ray tube. For years scientists had known that if an electric current was passed through a vacuum tube, a stream of glowing material could be seen; however, no one could explain why. Thomson found that the mysterious glowing stream would bend toward a positively charged electric plate. Thomson theorized, and was later proven correct, that the stream was in fact made up of small particles, pieces of atoms that carried a negative charge. These particles were later named electrons. The present day atom has electrons in it so that has not changed. His discovery played a huge part in the constructing of the present day model.
John Dalton-a study of Dalton's own laboratory notebooks, discovered in the rooms of the Lit & Phil, concluded that so far from Dalton being led by his search for an explanation of the law of multiple proportions to the idea that chemical combination consists in the interaction of atoms of definite and characteristic weight, the idea of atoms arose in his mind as a purely physical concept, forced upon him by study of the physical properties of the atmosphere and other gases. Dalton proceeded to print his first published table of relative atomic weights. Six elements appear in this table, namely hydrogen, oxygen, nitrogen, carbon, sulfur, and phosphorus, with the atom of hydrogen conventionally assumed to weigh 1. Dalton provided no indication in this first paper how he had arrived at these numbers. However, in his laboratory notebook under the date 6 September 1803 there appears a list in which he sets out the relative weights of the atoms of a number of elements, derived from analysis of water, ammonia, carbon dioxide, etc. by chemists of the time. His discoveries led to the discovery of a few elements his atomic theory has also played a major role in the new discoveries.
H.G.J Mosley-Before Moseley and his created law, atomic numbers had been thought of as a semi-arbitrary ordering number, vaguely increasing with atomic weight but not strictly defined by it. Moseley redefined the idea of atomic numbers from its previous status as an ad hoc numerical tag to help sorting the elements, in particular in the Periodic Table, into a real and objective whole-number quantity that was experimentally measurable. Furthermore, as noted by Bohr, Moseley's law provided a reasonably complete experimental set of data that supported the conception by Ernest Rutherford and Antonius Van den Broek of the atom, with a positively-charged nucleus surrounded by negatively-charged electrons in which the atomic number is understood to be the exactly physical number of positive charges in the central atomic nuclei of the elements. Simple modification of Rydberg's and Bohr's formulas were found to give theoretical justification for Moseley's empirically-derived law for determining atomic numbers. The atomic number is one of the most important things of an atom. It has helped us understand so much about current atoms. His dicovery was a very important and useful discovery.
Dmitri Mendeleev- Developed the first periodic table when trying to classify elements not by accidental or instinctive reasons, but by a set principle. He believed it should be numerical in nature to eliminate any margin of arbitrariness. The trend of increasing atomic mass allowed him to discover a periodicity of elemental properties. The first model used vertical columns and showed that there were some missing places where there could be undiscovered elements.
James Chadwick- discovered a third type of subatomic particle, which he named the neutron. Neutrons help stabilize the protons in the atom's nucleus. Because the nucleus is so tightly packed together, the positively charged protons would tend to repel each other normally. Neutrons help to reduce the repulsion between protons and stabilize the atom's nucleus. Neutrons always reside in the nucleus of atoms and they are about the same size as protons. However, neutrons do not have any electrical charge; they are electrically neutral.
Atoms are electrically neutral because the number of protons + charges is equal to the number of electrons - charges and thus the two cancel out. As the atom gets larger, the number of protons increases, and so does the number of electrons in the neutral state of the atom. The illustration linked below compares the two simplest atoms, hydrogen and helium. The present day model still consists of the protons. His discovery is still a very important factor today and for the present day atom.
gatorshelton
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.
Democritus:The theory of Democritus and Leucippus held that everything is composed of "atoms", which are physically, but not geometrically, indivisible; that between atoms lies empty space; that atoms are indestructible; have always been, and always will be, in motion; that there are an infinite number of atoms, and kinds of atoms, which differ in shape, and size. Of the mass of atoms, Democritus said "The more any indivisible exceeds, the heavier it is." But their exact position on weight of atoms is disputed.
Issac Newton: Newton laid the foundation for differential and integral calculus. His work on optics and gravitation make him one of the greatest scientists the world has known. Newton's greatest achievement was his work in physics and celestial mechanics, which culminated in the theory of universal gravitation. By 1666 Newton had early versions of his three laws of motion. He had also discovered the law giving the centrifugal force on a body moving uniformly in a circular path. However he did not have a correct understanding of the mechanics of circular motion.
john dalton:John Dalton developed the first useful atomic theory of matter around 1803. In the course of his studies on meteorology, Dalton concluded that evaporated water exists in air as an independent gas. He wondered how water and air could occupy the same space at the same time, when obviously solid bodies can't. If the water and air were composed of discrete particles, Dalton reasoned, evaporation might be viewed as a mixing of water particles with air particles. He performed a series of experiments on mixtures of gases to determine what effect properties of the individual gases had on the properties of the mixture as a whole. While trying to explain the results of those experiments, Dalton developed the hypothesis that the sizes of the particles making up different gases must be different.
J.J. Thomson: J J Thomson experimented on cathode rays. In Britain, physicists had argued these rays were particles, but German physicists disagreed, thinking they were a type of electromagnetic radiation. Thomson showed that cathode rays were particles with a negative electric charge and much smaller than an atom. He also thought all atoms contained them. These particles were later named electrons.
micheal faraday:Faraday's introduction of the concept of lines of force was rejected by most of the mathematical physicists of Europe, since they assumed that electric charges attract and repel one another, by action at a distance, making such lines unnecessary. Faraday had demonstrated the phenomenon of electromagnetism in a series of experiments, however. This experimental necessity probably led the physicist James Clerk Maxwell to accept the concept of lines of force and put Faraday's ideas into mathematical form, thus giving birth to modern field theory.
Dmitri Mendeleev: Arranged elements into 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of the their atomic weights". This became known as the Periodic Law.
albert einstein:Einstein's contributions to physics began in 1905 with three major results: the explanation of Brownian motion in terms of molecules; the explanation of the photoelectric effect in terms of the quantum; and the special theory of relativity that links time to space and energy to matter. From 1907 to 1915 Einstein developed general relativity, a theory of gravity more accurate than Newton's; it became the basis of theoretical cosmology. In failed efforts in the 1930s to refute the interpretation of quantum theory in terms of probability, Einstein contributed to the theoretical basis for what is sometimes called teleportation of photons (which Einstein called "spooky action at a distance"). His last major effort was an attempt to unify electromagnetism and gravity into a single unified field theory, still an active problem of physics.
niels bohr:Niels Bohr was a Danish physicist who made fundamental contributions to understanding atomic structure and quantum mechanics, for which he received the Nobel Prize in Physics in 1922. He was also part of the team of physicists working on the Manhattan Project. Bohr married Margrethe Nørlund in 1912, and one of their sons, Aage Niels Bohr, grew up to be an important physicist, who like his father received the Nobel prize, in 1975. Bohr is widely considered to be the one of the greatest physicists of the 20th century.
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.
Democritus:The theory of Democritus and Leucippus held that everything is composed of "atoms", which are physically, but not geometrically, indivisible; that between atoms lies empty space; that atoms are indestructible; have always been, and always will be, in motion; that there are an infinite number of atoms, and kinds of atoms, which differ in shape, and size. Of the mass of atoms, Democritus said "The more any indivisible exceeds, the heavier it is." But their exact position on weight of atoms is disputed.
Issac Newton: Newton laid the foundation for differential and integral calculus. His work on optics and gravitation make him one of the greatest scientists the world has known. Newton's greatest achievement was his work in physics and celestial mechanics, which culminated in the theory of universal gravitation. By 1666 Newton had early versions of his three laws of motion. He had also discovered the law giving the centrifugal force on a body moving uniformly in a circular path. However he did not have a correct understanding of the mechanics of circular motion.
john dalton:John Dalton developed the first useful atomic theory of matter around 1803. In the course of his studies on meteorology, Dalton concluded that evaporated water exists in air as an independent gas. He wondered how water and air could occupy the same space at the same time, when obviously solid bodies can't. If the water and air were composed of discrete particles, Dalton reasoned, evaporation might be viewed as a mixing of water particles with air particles. He performed a series of experiments on mixtures of gases to determine what effect properties of the individual gases had on the properties of the mixture as a whole. While trying to explain the results of those experiments, Dalton developed the hypothesis that the sizes of the particles making up different gases must be different.
J.J. Thomson: J J Thomson experimented on cathode rays. In Britain, physicists had argued these rays were particles, but German physicists disagreed, thinking they were a type of electromagnetic radiation. Thomson showed that cathode rays were particles with a negative electric charge and much smaller than an atom. He also thought all atoms contained them. These particles were later named electrons.
micheal faraday:Faraday's introduction of the concept of lines of force was rejected by most of the mathematical physicists of Europe, since they assumed that electric charges attract and repel one another, by action at a distance, making such lines unnecessary. Faraday had demonstrated the phenomenon of electromagnetism in a series of experiments, however. This experimental necessity probably led the physicist James Clerk Maxwell to accept the concept of lines of force and put Faraday's ideas into mathematical form, thus giving birth to modern field theory.
Dmitri Mendeleev: Arranged elements into 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of the their atomic weights". This became known as the Periodic Law.
albert einstein:Einstein's contributions to physics began in 1905 with three major results: the explanation of Brownian motion in terms of molecules; the explanation of the photoelectric effect in terms of the quantum; and the special theory of relativity that links time to space and energy to matter. From 1907 to 1915 Einstein developed general relativity, a theory of gravity more accurate than Newton's; it became the basis of theoretical cosmology. In failed efforts in the 1930s to refute the interpretation of quantum theory in terms of probability, Einstein contributed to the theoretical basis for what is sometimes called teleportation of photons (which Einstein called "spooky action at a distance"). His last major effort was an attempt to unify electromagnetism and gravity into a single unified field theory, still an active problem of physics.
niels bohr:Niels Bohr was a Danish physicist who made fundamental contributions to understanding atomic structure and quantum mechanics, for which he received the Nobel Prize in Physics in 1922. He was also part of the team of physicists working on the Manhattan Project. Bohr married Margrethe Nørlund in 1912, and one of their sons, Aage Niels Bohr, grew up to be an important physicist, who like his father received the Nobel prize, in 1975. Bohr is widely considered to be the one of the greatest physicists of the 20th century.
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.
Democritus: Started the idea that matter was composed of the tiny particles called "atoms".The theory of Democritus and Leucippus held that everything is composed of "atoms", which are physically, but not geometrically, indivisible; that between atoms lies empty space; that atoms are indestructible; have always been, and always will be, in motion; that there are an infinite number of atoms, and kinds of atoms, which differ in shape, and size. Of the mass of atoms, Democritus said "The more any indivisible exceeds, the heavier it is." But their exact position on weight of atoms is disputed. These were the things that composed all matter and the only differences were the size, shape, and weight. There was much speculation and without a clear way to prove the idea, they largely ignored his ramblings because they didn't have the technology to further study it. They didn’t look at this again for about 2000 years.
John Dalton: Credited with developing the atomic theory. His theory is as follows. 1. Matter is composed of small particles called atoms. 2. All atoms of an element are identical, but are different from those of any other element. 3. Atoms are neither created nor destroyed. 4. Atoms always combine in whole number multiples of each other. Dalton proceeded to print his first published table of relative atomic weights. Six elements appear in this table, namely hydrogen, oxygen, nitrogen, carbon, sulfur, and phosphorus, with the atom of hydrogen conventionally assumed to weigh 1. Dalton provided no indication in this first paper how he had arrived at these numbers. However, in his laboratory notebook under the date 6 September 1803[4] there appears a list in which he sets out the relative weights of the atoms of a number of elements, derived from analysis of water, ammonia, carbon dioxide, etc. by chemists of the time.
Dmitri Mendeleev: Developed the first periodic table when trying to classify elements not by accidental or instinctive reasons, but by a set principle. He believed it should be numerical in nature to eliminate any margin of arbitrariness. The trend of increasing atomic mass allowed him to discover a periodicity of elemental properties. The first model used vertical columns and showed that there were some missing places where there could be undiscovered elements. On 6 March 1869, Mendeleev made a formal presentation to the Russian Chemical Society, entitled The Dependence between the Properties of the Atomic Weights of the Elements, which described elements according to both atomic weight and valence. This presentation stated that 1.The elements, if arranged according to their atomic weight, exhibit an apparent periodicity of properties. 2.Elements which are similar in regards to their chemical properties have atomic weights which are either of nearly the same value (e.g., Pt, Ir, Os) or which increase regularly (e.g., K, Rb, Cs). 3. The arrangement of the elements in groups of elements in the order of their atomic weights corresponds to their so-called valencies, as well as, to some extent, to their distinctive chemical properties; as is apparent among other series in that of Li, Be, B, C, N, O, and F. 4.The elements which are the most widely diffused have small atomic weights. 5. The magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body. 6. We must expect the discovery of many yet unknown elements–for example, two elements, analogous to aluminum and silicon, whose atomic weights would be between 65 and 75. 7. The atomic weight of an element may sometimes be amended by knowledge of those of its contiguous elements. Thus the atomic weight of tellurium must lie between 123 and 126, and cannot be 128. Here Mendeleev seems to be wrong as the "atomic mass" of tellurium (127.6) remains higher than that of iodine (126.9) as displayed on modern periodic tables, but this is due to the way atomic masses are calculated, based on a weighted average of all of an element's common isotopes, not just the one-to-one proton/neutron-ratio version of the element to which Mendeleev was referring. 8. Certain characteristic properties of elements can be foretold from their atomic weights
Pierre and Marie Curie: These two worked in the discovery of radioactivity by following the notes of Henri Becquerel. In 1896 Henri Becquerel discovered that uranium salts emitted rays that resembled X-rays in their penetrating power. He demonstrated that this radiation, unlike phosphorescence, did not depend on an external source of energy, but seemed to arise spontaneously from uranium itself. Becquerel had, in fact, discovered radioactivity. Curie decided to look into uranium rays as a possible field of research for a thesis. She used a clever technique to investigate samples. Fifteen years earlier, her husband and his brother had invented the electrometer, a sensitive device for measuring electrical charge. Using the Curie electrometer, she discovered that uranium rays caused the air around a sample to conduct electricity. Using this technique, her first result was the finding that the activity of the uranium compounds depended only on the quantity of uranium present. She had shown that the radiation was not the outcome of some interaction of molecules, but must come from the atom itself. In scientific terms, this was the most important single piece of work that she conducted.
Ernest Rutherford: Determined that radiation was emitted from two different components of uranium. He unsuccessfully attempted to separate the two by using prisms of glass, aluminum, and paraffin wax. Using two positively charged plates, he identified the components as positive particles and lighter mass negative particles. During the investigation of radioactivity he coined the terms alpha and beta in 1899 to describe the two distinct types of radiation emitted by thorium and uranium. These rays were differentiated on the basis of penetrating power. From 1900 to 1903 he was joined at McGill by the young Frederick Soddy and they collaborated on research into the transmutation of elements. Rutherford had demonstrated that radioactivity was the spontaneous disintegration of atoms. He noticed that a sample of radioactive material invariably took the same amount of time for half the sample to decay—its "half-life"—and created a practical application using this constant rate of decay as a clock, which could then be used to help determine the age of the Earth, which turned out to be much older than most of the scientists at the time believed. In 1903, Rutherford realized that a type of radiation from radium discovered (but not named) by French chemist Paul Villard in 1900 must represent something different from alpha rays and beta rays, due to its very much greater penetrating power. Rutherford gave this third type of radiation its name also: the gamma ray.
J.J. Thomson: Until 1897, scientists believed atoms were indivisible; the ultimate particles of matter, but Thomson proved them wrong when he discovered that atoms contained particles known as electrons. Thomson discovered this through his explorations on the properties of cathode rays. Thomson found that the rays could be deflected by an electric field (in addition to magnetic fields, which was already known). By comparing the deflection of a beam of cathode rays by electric and magnetic fields he was able to measure the particle's mass. This showed that cathode rays were matter, but he found that the particles were about 2000 times lighter than the mass of the lightest atom, hydrogen. He concluded that the rays were composed of very light negatively charged particles which he called "corpuscles". Thomson believed that the corpuscles emerged from the atoms of the trace gas inside his cathode ray tubes. He thus concluded that atoms were divisible, and that the corpuscles were their building blocks. To explain the overall neutral charge of the atom, he proposed that the corpuscles were distributed in a uniform sea of positive charge; this was the plum pudding model as the electrons were embedded in the positive charge like plums in a plum pudding (although in Thomson's model they were not stationary).
Henry Mosley: Before Moseley's discovery, the atomic numbers (or elemental number) of an element had been thought of as a semi-arbitrary sequential number, based on the sequence of atomic masses, but modified somewhat where chemists found this to be desirable, such as by the great Russian chemist, Dmitri Ivanovich Mendeleev. In his invention of the Periodic Table of the Elements, Mendeleev had interchanged the orders of a few pairs of elements in order to put them in more appropriate places in this table of the elements. For example, the metals cobalt and nickel had been assigned the atomic numbers 27 and 28, respectively, based on their known chemical and physical properties, even though they have nearly the same atomic masses. In fact, the atomic mass of cobalt is slightly larger than that of nickel, which would have placed them in backwards order if they had been placed in the Periodic Table blindly according to atomic mass. Moseley's experiments in X-ray crystallography showed directly from their physics that cobalt and nickel have the different atomic numbers, 27 and 28, and that they are placed in the Periodic Table correctly by Moseley's objective measurements of their atomic numbers. Hence, Moseley's discovery demonstrated that the atomic numbers of elements are not just rather arbitrary numbers based on chemistry and the intuition of chemists, but rather, they have a firm experimental basis from the physics of their X-ray spectra.
James Chadwick: He solved the problem of the extra nuclear mass when he identified the neutron. This occurred while studying the radiation resulting from bombarding of beryllium with alpha particles. He noted a particle with approximately the same mass as a proton being released. He determined that, since the particle was not bent by electrical fields and was highly penetrating, it was electrically neutral. In 1932, Chadwick discovered a previously unknown particle in the atomic nucleus. This particle became known as the neutron because of its lack of electric charge. Chadwick's discovery was crucial for the fission of uranium 235. Unlike positively charged alpha particles, which are repelled by the electrical forces present in the nuclei of other atoms, neutrons do not need to overcome any Coulomb barrier and can therefore penetrate and split the nuclei of even the heaviest elements. For this discovery he was awarded the Hughes Medal of the Royal Society in 1932 and the Nobel Prize for Physics in 1935. Chadwick’s discovery made it possible to create elements heavier than uranium in the laboratory. His discovery particularly inspired Enrico Fermi, Italian physicist and Nobel laureate, to discover nuclear reactions brought by slowed neutrons, and led Lise Meitner, Otto Hahn and Fritz Strassmann, German radio chemists in Berlin, to the revolutionary discovery of “nuclear fission”.
Democritus: Started the idea that matter was composed of the tiny particles called "atoms".The theory of Democritus and Leucippus held that everything is composed of "atoms", which are physically, but not geometrically, indivisible; that between atoms lies empty space; that atoms are indestructible; have always been, and always will be, in motion; that there are an infinite number of atoms, and kinds of atoms, which differ in shape, and size. Of the mass of atoms, Democritus said "The more any indivisible exceeds, the heavier it is." But their exact position on weight of atoms is disputed. These were the things that composed all matter and the only differences were the size, shape, and weight. There was much speculation and without a clear way to prove the idea, they largely ignored his ramblings because they didn't have the technology to further study it. They didn’t look at this again for about 2000 years.
John Dalton: Credited with developing the atomic theory. His theory is as follows. 1. Matter is composed of small particles called atoms. 2. All atoms of an element are identical, but are different from those of any other element. 3. Atoms are neither created nor destroyed. 4. Atoms always combine in whole number multiples of each other. Dalton proceeded to print his first published table of relative atomic weights. Six elements appear in this table, namely hydrogen, oxygen, nitrogen, carbon, sulfur, and phosphorus, with the atom of hydrogen conventionally assumed to weigh 1. Dalton provided no indication in this first paper how he had arrived at these numbers. However, in his laboratory notebook under the date 6 September 1803[4] there appears a list in which he sets out the relative weights of the atoms of a number of elements, derived from analysis of water, ammonia, carbon dioxide, etc. by chemists of the time.
Dmitri Mendeleev: Developed the first periodic table when trying to classify elements not by accidental or instinctive reasons, but by a set principle. He believed it should be numerical in nature to eliminate any margin of arbitrariness. The trend of increasing atomic mass allowed him to discover a periodicity of elemental properties. The first model used vertical columns and showed that there were some missing places where there could be undiscovered elements. On 6 March 1869, Mendeleev made a formal presentation to the Russian Chemical Society, entitled The Dependence between the Properties of the Atomic Weights of the Elements, which described elements according to both atomic weight and valence. This presentation stated that 1.The elements, if arranged according to their atomic weight, exhibit an apparent periodicity of properties. 2.Elements which are similar in regards to their chemical properties have atomic weights which are either of nearly the same value (e.g., Pt, Ir, Os) or which increase regularly (e.g., K, Rb, Cs). 3. The arrangement of the elements in groups of elements in the order of their atomic weights corresponds to their so-called valencies, as well as, to some extent, to their distinctive chemical properties; as is apparent among other series in that of Li, Be, B, C, N, O, and F. 4.The elements which are the most widely diffused have small atomic weights. 5. The magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body. 6. We must expect the discovery of many yet unknown elements–for example, two elements, analogous to aluminum and silicon, whose atomic weights would be between 65 and 75. 7. The atomic weight of an element may sometimes be amended by knowledge of those of its contiguous elements. Thus the atomic weight of tellurium must lie between 123 and 126, and cannot be 128. Here Mendeleev seems to be wrong as the "atomic mass" of tellurium (127.6) remains higher than that of iodine (126.9) as displayed on modern periodic tables, but this is due to the way atomic masses are calculated, based on a weighted average of all of an element's common isotopes, not just the one-to-one proton/neutron-ratio version of the element to which Mendeleev was referring. 8. Certain characteristic properties of elements can be foretold from their atomic weights
Pierre and Marie Curie: These two worked in the discovery of radioactivity by following the notes of Henri Becquerel. In 1896 Henri Becquerel discovered that uranium salts emitted rays that resembled X-rays in their penetrating power. He demonstrated that this radiation, unlike phosphorescence, did not depend on an external source of energy, but seemed to arise spontaneously from uranium itself. Becquerel had, in fact, discovered radioactivity. Curie decided to look into uranium rays as a possible field of research for a thesis. She used a clever technique to investigate samples. Fifteen years earlier, her husband and his brother had invented the electrometer, a sensitive device for measuring electrical charge. Using the Curie electrometer, she discovered that uranium rays caused the air around a sample to conduct electricity. Using this technique, her first result was the finding that the activity of the uranium compounds depended only on the quantity of uranium present. She had shown that the radiation was not the outcome of some interaction of molecules, but must come from the atom itself. In scientific terms, this was the most important single piece of work that she conducted.
Ernest Rutherford: Determined that radiation was emitted from two different components of uranium. He unsuccessfully attempted to separate the two by using prisms of glass, aluminum, and paraffin wax. Using two positively charged plates, he identified the components as positive particles and lighter mass negative particles. During the investigation of radioactivity he coined the terms alpha and beta in 1899 to describe the two distinct types of radiation emitted by thorium and uranium. These rays were differentiated on the basis of penetrating power. From 1900 to 1903 he was joined at McGill by the young Frederick Soddy and they collaborated on research into the transmutation of elements. Rutherford had demonstrated that radioactivity was the spontaneous disintegration of atoms. He noticed that a sample of radioactive material invariably took the same amount of time for half the sample to decay—its "half-life"—and created a practical application using this constant rate of decay as a clock, which could then be used to help determine the age of the Earth, which turned out to be much older than most of the scientists at the time believed. In 1903, Rutherford realized that a type of radiation from radium discovered (but not named) by French chemist Paul Villard in 1900 must represent something different from alpha rays and beta rays, due to its very much greater penetrating power. Rutherford gave this third type of radiation its name also: the gamma ray.
J.J. Thomson: Until 1897, scientists believed atoms were indivisible; the ultimate particles of matter, but Thomson proved them wrong when he discovered that atoms contained particles known as electrons. Thomson discovered this through his explorations on the properties of cathode rays. Thomson found that the rays could be deflected by an electric field (in addition to magnetic fields, which was already known). By comparing the deflection of a beam of cathode rays by electric and magnetic fields he was able to measure the particle's mass. This showed that cathode rays were matter, but he found that the particles were about 2000 times lighter than the mass of the lightest atom, hydrogen. He concluded that the rays were composed of very light negatively charged particles which he called "corpuscles". Thomson believed that the corpuscles emerged from the atoms of the trace gas inside his cathode ray tubes. He thus concluded that atoms were divisible, and that the corpuscles were their building blocks. To explain the overall neutral charge of the atom, he proposed that the corpuscles were distributed in a uniform sea of positive charge; this was the plum pudding model as the electrons were embedded in the positive charge like plums in a plum pudding (although in Thomson's model they were not stationary).
Henry Mosley: Before Moseley's discovery, the atomic numbers (or elemental number) of an element had been thought of as a semi-arbitrary sequential number, based on the sequence of atomic masses, but modified somewhat where chemists found this to be desirable, such as by the great Russian chemist, Dmitri Ivanovich Mendeleev. In his invention of the Periodic Table of the Elements, Mendeleev had interchanged the orders of a few pairs of elements in order to put them in more appropriate places in this table of the elements. For example, the metals cobalt and nickel had been assigned the atomic numbers 27 and 28, respectively, based on their known chemical and physical properties, even though they have nearly the same atomic masses. In fact, the atomic mass of cobalt is slightly larger than that of nickel, which would have placed them in backwards order if they had been placed in the Periodic Table blindly according to atomic mass. Moseley's experiments in X-ray crystallography showed directly from their physics that cobalt and nickel have the different atomic numbers, 27 and 28, and that they are placed in the Periodic Table correctly by Moseley's objective measurements of their atomic numbers. Hence, Moseley's discovery demonstrated that the atomic numbers of elements are not just rather arbitrary numbers based on chemistry and the intuition of chemists, but rather, they have a firm experimental basis from the physics of their X-ray spectra.
James Chadwick: He solved the problem of the extra nuclear mass when he identified the neutron. This occurred while studying the radiation resulting from bombarding of beryllium with alpha particles. He noted a particle with approximately the same mass as a proton being released. He determined that, since the particle was not bent by electrical fields and was highly penetrating, it was electrically neutral. In 1932, Chadwick discovered a previously unknown particle in the atomic nucleus. This particle became known as the neutron because of its lack of electric charge. Chadwick's discovery was crucial for the fission of uranium 235. Unlike positively charged alpha particles, which are repelled by the electrical forces present in the nuclei of other atoms, neutrons do not need to overcome any Coulomb barrier and can therefore penetrate and split the nuclei of even the heaviest elements. For this discovery he was awarded the Hughes Medal of the Royal Society in 1932 and the Nobel Prize for Physics in 1935. Chadwick’s discovery made it possible to create elements heavier than uranium in the laboratory. His discovery particularly inspired Enrico Fermi, Italian physicist and Nobel laureate, to discover nuclear reactions brought by slowed neutrons, and led Lise Meitner, Otto Hahn and Fritz Strassmann, German radio chemists in Berlin, to the revolutionary discovery of “nuclear fission”.
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.
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.
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.
Democritus, Dalton, Mendeleev, JJ Thomson, Rutherford, Moseley, Bohr, Chadwick,
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. This led to Dalton with how Dalton looked at his theory.
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 that 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, that 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.
Mendeleev- organized the periodic table by the elements atomic weight and properties. Predicted where there was gaps 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 lifetimeógallium, scandium, and germanium. This helped with understanding the universe and how things are in the world. Mendeleev helped with Moseley to see that the PT needed to be arranged by atomic number.
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.
Rutherford- Discovered that atoms of the heavier elements disintegrate into radiation. Rutherford also used the gold foil experiment to find that there was 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. Bohr helped with the quantum model by showing that there were electron energy levels and that they belonged to a certain level.
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 the whole atom and the things inside. Chadwick used a different type of experiment to track particle radiation. This 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 finally equal. This helped show where to put neutrons providing that they did not bond with any other particle.
Question 1B
Examine the history of the development of the atom. We have already discussed themajor players in the development of the atom. Pick out at least 8 major players whohelped aid in the development of the concept of the atom. Then explain eachexperiment in a concise explanation. Then explain how each one aided in thedevelopment of the next or how their concept assisted in the further development of the current quantum model of the atom.
J.J. Thomson- In 1897 the British physicist Joseph John (J. J.) Thomson (1856–1940) discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube, an area being investigated by numerous scientists at the time. Thomson interpreted the deflection of the rays by electrically charged plates and magnets as evidence of "bodies much smaller than atoms" that he calculated as having a very large value for the charge-to-mass ratio. Later he estimated the value of the charge itself.
In 1904 Thomson suggested a model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces. His efforts to estimate the number of electrons in an atom from measurements of the scattering of light, X, beta, and gamma rays initiated the research trajectory along which his student Ernest Rutherford moved.
Ernest Rutherford- publishes his atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons. This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space. Rutherford came to this conclusion following the results of his famous gold foil experiment. This experiment involved the firing of radioactive particles through minutely thin metal foils (notably gold) and detecting them using screens coated with zinc sulfide (a scintillator). Rutherford found that although the vast majority of particles passed straight through the foil approximately 1 in 8000 were deflected leading him to his theory that most of the atom was made up of 'empty space'.
Democritus- Democritus argued that all matter consists of tiny, physically invisible particles. The Greek word atomos, in fact, means "indivisible." Democritus taught that an infinite number of atoms exist and that they are in constant motion. The space between atoms, he said, is occupied by a void. Atoms were never created, according to Democritus, but have always existed, just as they are now. They are also eternal; that is, they cannot be destroyed.. Atoms have physical properties that explain the properties of matter, he said. Atoms of water, for example, are round and smooth, permitting them to slide over each other; conversely, atoms of fire have jagged edges.
Bohr- A model of the atom, first described by Niels Bohr, that explains the emission and absorption of radiation as transitions between stationary electronic states in which the electron orbits the nucleus at a definite distance. The Bohr model violates the Heisenberg uncertainty principle, since it postulates definite paths and momenta for electrons as they move around the nucleus. Modern theories usually use atomic orbitals to describe the behavior of electrons in atoms.
John Dalton-English meteorologist who switched to chemistry when he saw the applications for chemistry of his ideas about the atmosphere. He proposed the Atomic Theory in 1803 which stated that (1) all matter was composed of small indivisible particles termed atoms, (2) atoms of a given element possess unique characteristics and weight, and (3) three types of atoms exist: simple (elements), compound (simple molecules), and complex (complex molecules). Dalton's theory was presented in New System of Chemical Philosophy (1808-1827). This work identified chemical elements as a specific type of atom, therefore rejecting Newton's theory of chemical affinities.
Lavoisier- Lavoisier is now known as the Father of Modern Chemistry. However, when Lavoisier started his experiments on combustion and respiration, chemistry was still in the very early stages of development. There was lots of empirical information but very little theoretical basis and no formal language. Enough characteristics of acids, alkalis, salts and metals were known so that they could usually be distinguished, but gases were hardly known to exist. Lavoisier was an excellent discoverer because he was quick to see the significance of new findings. He readily confirmed and extended the experimental discoveries of others and formed mental models to organize all of these ideas. He was one of the few chemists at the time to fully appreciate the importance of careful measurements of reactants and products. In order to make such careful measurements he invented a balance which was good to about .0005 grams. He proved the Law of Conservation of Mass, showing that the mass of the reactants had to equal the mass of the products.
William Crookes- He soon discovered the phenomenon upon which depends the action of the well-known little instrument, the Crookes radiometer, in which a system of vanes, each blackened on one side and polished on the other, is set in rotation when exposed to radiant energy. He did not, however, provide the true explanation of this apparent "attraction and repulsion resulting from radiation". Of more fundamental importance were his researches on the passage of the electrical discharge through rarefied gases. He found that as the attenuation of the gas was made greater the dark space round the negative electrode extended, while rays, now known as cathode rays, proceed from the electrode. He investigated the properties of the rays, showing that they travel in straight lines, cause phosphorescence in objects upon which they impinge, and by their impact produce great heat. He believed that he had discovered a fourth state of matter, which he called "radiant matter". But his theoretical views on the nature of "radiant matter" proved to be mistaken. He believed the rays to consist of streams of particles of ordinary molecular magnitude. It remained for (Sir) J. J. Thomson to discover their subatomic nature, and to prove that cathode rays consist of streams of negative electrons, that is, of negatively electrified particles whose mass is only 1/1,800 that of the atom of hydrogen.
James Chadwick- Chadwick's own research focused on radioactivity. In 1919 Rutherford developed a theory on the atom's nucleaus and theorized on the existence of a neuron, a non charged particle within the atom's nucleus. But they and other researchers were finding that the neutron did not seem to be the only particle in the nucleus.
As they studied atomic disintegration, they kept seeing that the atomic number (number of protons in the nucleus, equivalent to the positive charge of the atom) was less than the atomic mass (average mass of the atom). For example, a helium atom has an atomic mass of 4, but an atomic number (or positive charge) of 2. Since electrons have almost no mass, it seemed that something besides the protons in the nucleus were adding to the mass. One leading explanation was that there were electrons and additional protons in the nucleus as well -- the protons still contributed their mass but their positive charge was canceled out by the negatively charged electrons. So in the helium example, there would be four protons and two electrons in the nucleus to yield a mass of 4 but a charge of only 2. Rutherford also put out the idea that there could be a particle with mass but no charge. He called it a neutron, and imagined it as a paired proton and electron. There was no evidence for any of these ideas.
J.J. Thomson- In 1897 the British physicist Joseph John (J. J.) Thomson (1856–1940) discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube, an area being investigated by numerous scientists at the time. Thomson interpreted the deflection of the rays by electrically charged plates and magnets as evidence of "bodies much smaller than atoms" that he calculated as having a very large value for the charge-to-mass ratio. Later he estimated the value of the charge itself.
In 1904 Thomson suggested a model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces. His efforts to estimate the number of electrons in an atom from measurements of the scattering of light, X, beta, and gamma rays initiated the research trajectory along which his student Ernest Rutherford moved.
Ernest Rutherford- publishes his atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons. This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space. Rutherford came to this conclusion following the results of his famous gold foil experiment. This experiment involved the firing of radioactive particles through minutely thin metal foils (notably gold) and detecting them using screens coated with zinc sulfide (a scintillator). Rutherford found that although the vast majority of particles passed straight through the foil approximately 1 in 8000 were deflected leading him to his theory that most of the atom was made up of 'empty space'.
Democritus- Democritus argued that all matter consists of tiny, physically invisible particles. The Greek word atomos, in fact, means "indivisible." Democritus taught that an infinite number of atoms exist and that they are in constant motion. The space between atoms, he said, is occupied by a void. Atoms were never created, according to Democritus, but have always existed, just as they are now. They are also eternal; that is, they cannot be destroyed.. Atoms have physical properties that explain the properties of matter, he said. Atoms of water, for example, are round and smooth, permitting them to slide over each other; conversely, atoms of fire have jagged edges.
Bohr- A model of the atom, first described by Niels Bohr, that explains the emission and absorption of radiation as transitions between stationary electronic states in which the electron orbits the nucleus at a definite distance. The Bohr model violates the Heisenberg uncertainty principle, since it postulates definite paths and momenta for electrons as they move around the nucleus. Modern theories usually use atomic orbitals to describe the behavior of electrons in atoms.
John Dalton-English meteorologist who switched to chemistry when he saw the applications for chemistry of his ideas about the atmosphere. He proposed the Atomic Theory in 1803 which stated that (1) all matter was composed of small indivisible particles termed atoms, (2) atoms of a given element possess unique characteristics and weight, and (3) three types of atoms exist: simple (elements), compound (simple molecules), and complex (complex molecules). Dalton's theory was presented in New System of Chemical Philosophy (1808-1827). This work identified chemical elements as a specific type of atom, therefore rejecting Newton's theory of chemical affinities.
Lavoisier- Lavoisier is now known as the Father of Modern Chemistry. However, when Lavoisier started his experiments on combustion and respiration, chemistry was still in the very early stages of development. There was lots of empirical information but very little theoretical basis and no formal language. Enough characteristics of acids, alkalis, salts and metals were known so that they could usually be distinguished, but gases were hardly known to exist. Lavoisier was an excellent discoverer because he was quick to see the significance of new findings. He readily confirmed and extended the experimental discoveries of others and formed mental models to organize all of these ideas. He was one of the few chemists at the time to fully appreciate the importance of careful measurements of reactants and products. In order to make such careful measurements he invented a balance which was good to about .0005 grams. He proved the Law of Conservation of Mass, showing that the mass of the reactants had to equal the mass of the products.
William Crookes- He soon discovered the phenomenon upon which depends the action of the well-known little instrument, the Crookes radiometer, in which a system of vanes, each blackened on one side and polished on the other, is set in rotation when exposed to radiant energy. He did not, however, provide the true explanation of this apparent "attraction and repulsion resulting from radiation". Of more fundamental importance were his researches on the passage of the electrical discharge through rarefied gases. He found that as the attenuation of the gas was made greater the dark space round the negative electrode extended, while rays, now known as cathode rays, proceed from the electrode. He investigated the properties of the rays, showing that they travel in straight lines, cause phosphorescence in objects upon which they impinge, and by their impact produce great heat. He believed that he had discovered a fourth state of matter, which he called "radiant matter". But his theoretical views on the nature of "radiant matter" proved to be mistaken. He believed the rays to consist of streams of particles of ordinary molecular magnitude. It remained for (Sir) J. J. Thomson to discover their subatomic nature, and to prove that cathode rays consist of streams of negative electrons, that is, of negatively electrified particles whose mass is only 1/1,800 that of the atom of hydrogen.
James Chadwick- Chadwick's own research focused on radioactivity. In 1919 Rutherford developed a theory on the atom's nucleaus and theorized on the existence of a neuron, a non charged particle within the atom's nucleus. But they and other researchers were finding that the neutron did not seem to be the only particle in the nucleus.
As they studied atomic disintegration, they kept seeing that the atomic number (number of protons in the nucleus, equivalent to the positive charge of the atom) was less than the atomic mass (average mass of the atom). For example, a helium atom has an atomic mass of 4, but an atomic number (or positive charge) of 2. Since electrons have almost no mass, it seemed that something besides the protons in the nucleus were adding to the mass. One leading explanation was that there were electrons and additional protons in the nucleus as well -- the protons still contributed their mass but their positive charge was canceled out by the negatively charged electrons. So in the helium example, there would be four protons and two electrons in the nucleus to yield a mass of 4 but a charge of only 2. Rutherford also put out the idea that there could be a particle with mass but no charge. He called it a neutron, and imagined it as a paired proton and electron. There was no evidence for any of these ideas.
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