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Atomic Structure Atomic Structure

The ancient Greek philosophers Leucippus and Democritus believed that atoms existed, but they had no idea as to their nature. Centuries later, in 1803, the English chemist John Dalton, guided by the experimental fact that chemical elements cannot be decomposed chemically, was led to formulate his atomic theory. Dalton's atomic theory was based on the assumption that atoms are tiny indivisible entities, with each chemical element consisting of its own characteristic atoms.✶ ✶See Atoms article for further discussion of Dalton's atomic theory. The atom is now known to consist of three primary particles: protons, neutrons, and electrons, which make up the atoms of all matter. A series of experimental facts established the validity of the model. Radioactivity played an important part. Marie Curie suggested, in 1899, that when atoms disintegrate, they contradict Dalton's idea that atoms are indivisible. There must then be something smaller than the atom (subatomic particles) of which atoms were composed. Long before that, Michael Faraday's electrolysis experiments and laws suggested that, just as an atom is the fundamental particle of an element, a fundamental particle for electricity must exist. The "particle" of electricity was given the name electron. Experiments with cathode-ray tubes, conducted by the British physicist Joseph John Thomson, proved the existence of the electron and obtained the charge-to-mass ratio for it. The experiments suggested that electrons are present in all kinds of matter and that they presumably exist in all atoms of all elements. Efforts were then turned to measuring the charge on the electron, and these were eventually successful by the American physicist Robert Andrews Millikan through the famous oil drop experiment. The study of the so-called canal rays by the German physicist Eugen Goldstein, observed in a special cathode-ray tube with a perforated cathode, let to the recognition in 1902 that these rays were positively charged particles (protons ). Finally, years later in 1932 the British physicist James Chadwick discovered another particle in the nucleus that had no charge, and for this reason was named neutron. As a physical chemist, George Stoney made significant contributions to our understanding of molecular motion. However, this Irish scientist is better known for assigning a name to negative atomic charges, electrons, while addressing the Royal Society of Dublin in 1891. —Valerie Borek Joseph John Thomson had supposed that an atom was a uniform sphere of positively charged matter within which electrons were circulating (the "plum-pudding" model). Then, around the year 1910, Ernest Ruthorford (who had discovered earlier that alpha rays consisted of positively charged particles having the mass of helium atoms) was led to the following model for the atom: Protons and neutrons exist in a very small nucleus, which means that the tiny nucleus contains all the positive charge and most of the mass of the atom, while negatively charged electrons surround the nucleus and occupy most of the volume of the atom. In formulating his model, Rutherford was assisted by Hans Geiger and Ernest Marsden, who found that when alpha particles hit a thin gold foil, almost all passed straight through, but very few (only 1 in 20,000) were deflected at large angles, with some coming straight back. Rutherford remarked later that it was as if you fired a 15-inch artillery shell at a sheet of paper and it bounced back and hit you. The deflected particles suggested that the atom has a very tiny nucleus that is extremely dense and positive in charge. Also working with Rutherford was Henry G. J. Moseley who, in 1913, performed an important experiment. When various metals were bombarded with electrons in a cathode-ray tube, they emitted X rays, the wavelengths of which were related to the nuclear charge of the metal atoms. This led to the law of chemical periodicity, which provided refinement of the periodic table introduced by Mendeleev in 1869. According to this law, all atoms of an element have the same number of protons in the nucleus. It is called the atomic number and is given the symbol Z. Hydrogen is the simplest element and has Z = 1. Through Rutherford's work it was known that that electrons are arranged in the space surrounding the atomic nucleus. A planetary model of the atom, with the electrons moving in circular orbits around the nucleus seemed an acceptable model. However, such a "dynamic model" violated the laws of classical electrodynamics, according to which a charged particle, such as an electron, moving in the positive electric field of the nucleus, should lose energy by radiation and eventually spiral into the nucleus. To solve this contradiction, in 1913, the Danish physicist Neils Bohr (then studying under Rutherford) postulated that the electron orbiting the nucleus could move only in certain orbits, having in each a certain "quantized" energy. It turns out that the colors in fireworks would help prove him right. The colorful lights of fireworks are emitted by "excited" atoms; that is, by atoms that have absorbed extra energy. Light consists of electromagnetic waves, each (monochromatic) color with a characteristic wavelength λ and frequency v. Frequency is related to energy E through the famous Planck equation, E = hν, where h is Planck's constant (6.6256 x 10−34 J s). Note that white light, such as sunlight, is a mixture of light of all colors, so it does not have a characteristic wavelength. For this reason we say that white light has a "continuous spectrum." On the other hand, excited atoms emit a "line spectrum" consisting of a set of monochromatic visible radiations. Each element has a characteristic line spectrum that can be used to identify the element. Note that line emission spectra can also be obtained by heating a salt of a metal with a flame. For instance, common salt (sodium chloride) provides a strong yellow light to the flame coming from excited sodium, while copper salts emit a blue-green light and lithium salts a red light. The colors of fireworks are due to this phenomenon. Scientists in the late nineteenth century tried to quantify the line spectra of the elements. In 1885 the Swedish school teacher Johann Balmer discovered a series of lines in the visible spectrum of hydrogen, the wavelengths of which could be related with a simple equation: in which λ is wavelength, k is constant, a = 2, and b = 3, 4, 5, … This group of lines was called the Balmer series. For the red line b = 3, for the green line b = 4, and for the blue line b = 5. Similar series were further discovered: in the infrared region, the Paschen series (with a = 3 and b = 4, 5 … in the above equation), and much later in the ultraviolet region, the Lyman series (with a = 1 and b = 2, 3 …). In 1896 the Swedish spectroscopist Johannes Rydberg developed a general equation that allowed the calculation of the wavelength of the red, green, and blue lines in the atomic spectrum of hydrogen: where nL is the number of the lower energy level to which an electron falls and nH is the number of the higher energy level from which it falls. R is called the Rydberg constant (1.0974 x 10−7 m−1). R was later shown to be 2π 2me 4Z2/h 3c, where m is the mass of the electron, e is its charge, Z is the atomic number, h is Planck's constant, and c is the speed of light. As noted earlier, Bohr had suggested the quantization of Ruthford's model of the atom. Although he was not aware of the work of Balmer and Paschen when he wrote the first version of his 1913 article, he had incorporated Planck's constant h into his model, which turned out to be an important decision. Bohr assumed that the absorption or emission of radiation can occur only by "jumps" of the electron from one stationary orbit to another. (See Figure 1.) The energy differences between two such allowed orbits then provided the characteristic frequencies of the emitted light. ΔE = E n1 − E n2 = hν Planck's constant h was named by Bohr the "quantum of action." Bohr's theory was in close agreement with many experimental facts regarding one-electron atoms (the hydrogen


Along the extreme right-hand column of the periodic table of elements is a group known as the noble gases: helium, neon, argon, krypton, xenon, and radon. Also known as the rare gases, they once were called inert gases, because scientists believed them incapable of reacting with other elements. Rare though they are, these gases are a part of everyday life, as evidenced by the helium in balloons, the neon in signs—and the harmful radon in some American homes. The periodic table of elements is ordered by the number of protons in the nucleus of an atom for a given element (the atomic number), yet the chart is also arranged in such a way that elements with similar characteristics are grouped together. Such is the case with Group 8, which is sometimes called Group 18, a collection of non-metals known as the noble gases. The six noble gases are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Their atomic numbers are, respectively, 2, 10, 18, 36, 54, and 86. Several characteristics, aside from their placement on the periodic table, define the noble gases. Obviously, all are gases, meaning that they only form liquids or solids at extremely low temperatures—temperatures that, on Earth at least, are usually only achieved in a laboratory. They are colorless, odorless, and tasteless, as well as monatomic—meaning that they exist as individual atoms, rather than in molecules. (By contrast, atoms of oxygen—another gas, though not among this group—usually combine to form a molecule, O2.) There is a reason why noble gas atoms tend not to combine: one of the defining characteristics of the noble gas "family" is their lack of chemical reactivity. Rather than reacting to, or bonding with, other elements, the noble gases tend to remain apart—hence the name "noble," implying someone or something that is set apart from the crowd, as it were. Due to their apparent lack of reactivity, the noble gases—also known as the rare gases—were once known as the inert gases. Indeed, helium, neon, and argon have not been found to combine with other elements to form compounds. However, in 1962 English chemist Neil Bartlett (1932-) succeeded in preparing a compound of xenon with platinum and fluorine (XePtF6), thus overturning the idea that the noble gases were entirely "inert." Since that time, numerous compounds of xenon with other elements, most notably oxygen and fluorine, have been developed. Fluorine has also been used to form simple compounds with krypton and radon. Nonetheless, low reactivity—instead of no reactivity, as had formerly been thought—characterizes the rare gases. One of the factors governing the reactivity of an element is its electron configuration, and the electrons of the noble gases are arranged in such a way as to discourage bonding with other elements. Helium is an unusual element in many respects—not least because it is the only element to have first been identified in the Solar System before it was discovered on Earth. This is significant, because the elements on Earth are the same as those found in space: thus, it is more than just an attempt at sounding poetic when scientists say that humans, as well as the world around them, are made from "the stuff of stars." In 1868, a French astronomer named Pierre Janssen (1824-1907) was in India to observe a total solar eclipse. To aid him in his observations, he used a spectroscope, an instrument for analyzing the spectrum of light emitted by an object. What Janssen's spectroscope showed was surprising: a yellow line in the spectrum, never seen before, which seemed to indicate the presence of a previously undiscovered element. Janssen called it "helium" after the Greek god Helios, or Apollo, whom the ancients associated with the Sun. Janssen shared his findings with English astronomer Sir Joseph Lockyer (1836-1920), who had a worldwide reputation for his work in analyzing light waves. Lockyer, too, believed that what Janssen had seen was a new element, and a few months later, he observed the same unusual spectral lines. At that time, the spectroscope was still a new invention, and many members of the worldwide scientific community doubted its usefulness, and therefore, in spite of Lockyer's reputation, they questioned the existence of this "new" element. Yet during their lifetimes, Janssen and Lockyer were proven correct. They had to wait a quarter century, however. In 1893, English chemist Sir William Ramsay (1852-1916) became intrigued by the presence of a mysterious gas bubble left over when nitrogen from the atmosphere was combined with oxygen. This was a phenomenon that had also been noted by English physicist Henry Cavendish (1731-1810) more than a century before, but Cavendish could offer no explanation. Ramsay, on the other hand, had the benefit of observations made by English physicist John William Strutt, Lord Rayleigh (1842-1919). Up to that time, scientists believed that air consisted only of oxygen, carbon dioxide, and water vapor. However, Rayleigh had noticed that when nitrogen was extracted from air after a process of removing those other components, it had a slightly higher density than nitrogen prepared from a chemical reaction. In light of his own observations, Ramsay concluded that whereas nitrogen obtained from chemical reactions was pure, the nitrogen extracted from air contained trace amounts of an unknown gas. Ramsay was wrong in only one respect: hidden with the nitrogen was not one gas, but five. In order to isolate these gases, Ramsay and Rayleigh subjected air to a combination of high pressure and low temperature, allowing the various gases to boil off at different temperatures. One of the gases was helium—the first confirmation that the element existed on Earth—but the other four gases were previously unknown. The Greek roots of the names given to the four gases reflected scientists' wonder at discovering these hard-to-find elements: neos (new), argos (in active), kryptos (hidden), and xenon (stranger). Inspired by the studies of Polish-French physicist and chemist Marie Curie (1867-1934) regarding the element radium and the phenomenon of radioactivity (she discovered the element, and coined the latter term), German physicist Friedrich Dorn (1848-1916) became fascinated with radium. Studying the element, he discovered that it emitted a radioactive gas, which he dubbed "radium emanation." Eventually, however, he realized that what was being produced was a new element. This was the first clear proof that one element could become another through the process of radioactive decay. Ramsay, who along with Rayleigh had received the Nobel Prize in 1904 for his work on the noble gases, was able to map the new element's spectral lines and determine its density and atomic mass. A few years later, in 1918, another scientist named C. Schmidt gave it the name "radon." Due to its behavior and the configuration of its electrons, chemists classified radon among what they continued to call the "inert gases" for another half-century—until Bartlett's preparation of xenon compounds in 1962. Though the rare gases are found in minerals and meteorites on Earth, their greatest presence is in the planet's atmosphere. It is believed that they were released into the air long ago as a by-product of decay on the part of radioactive materials in the Earth's crust. Within the atmosphere, argon is the most "abundant"—in comparative terms, given the fact that the "rare gases" are, by definition, rare. Nitrogen makes up about 78% of Earth's atmosphere and oxygen 21%, meaning that these two elements constitute fully 99% of the air above the Earth. Argon ranks a distant third, with 0.93%. The remaining 0.07% is made up on water vapor, carbon dioxide, ozone (O3), and traces of the noble gases. These are present in such small quantities that the figures for them are not typically presented as percentages, but rather in terms of parts per million (ppm). The concentrations of neon, helium, krypton, and xenon in the atmosphere are 18, 5, 1, and 0.09 ppm respectively. Radon in the atmosphere is virtually negligible, which is a fortunate thing, in light of its

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Answers:FOREIGN CHEMISTS Emil Abderhalden - a Swiss biochemist and physiologist. He was born in Oberuzwil in the Canton of St. Gallen in Switzerland. Emil Abderhalden studied medicine at the University of Basel and received his doctorate in 1902. He then studied in the laboratory of Emil Fischer and worked at the University of Berlin. In 1911 he moved to the University of Halle and taught physiology in the medical school. From 1931 to 1950, he was president of the German Academy of Natural Scientists Leopoldina. During World War I, he established a children's hospital and organized the removal of malnourished children to Switzerland. Subsequently, he resumed his research into physiological chemistry and began to study metabolism and food chemistry. Richard Abegg- a German chemist and pioneer of valence theory. Because of his research he proposed that the difference of the maximum positive and negative valence of an element tends to be eight. This has become to be called Abegg's rule. He was a gas balloon enthusiast and this is what caused his death at the age of 41 when he crashed in his balloon Schlesien.rom 1901, Abegg was active with an electrochemistry journal as editor.Abegg introduced the concept of the electro-affinity into chemistry and made the basis for the handbook of the inorganic chemistry (1905 1939). In 1904, Abegg formulated the valence rule, after which the highest positive and highest negative electro-valence of an element yields 8 altogether. This is called called Abegg's rule. Amedeo Avogadro-Lorenzo Romano Amedeo Carlo Avogadro, Count of Quaregna and Cerreto (August 9, 1776 July 9, 1856) was an Italian savant chemist, most noted for his contributions to the theory of molarity and molecular weight. As a tribute to him, the number of atoms of one mole of a substance, 6.02 \times 10 ^ {23} is known as Avogadro's number. Johannes Nicolaus Br nsted- a Danish physical chemist. He received a degree in chemical engineering in 1899 and his Ph. D. in 1908 from the University of Copenhagen. He was immediately appointed professor of inorganic and physical chemistry at Copenhagen. In 1906 he published his first of many papers on electron affinity. In 1923 he introduced the protonic theory of acid-base reactions, simultaneously with the English chemist Thomas Martin Lowry. The same year, the electronic theory was proposed by Gilbert N. Lewis, but both theories are commonly used.He became known as an authority on catalysis by acids and bases. He has the Br nsted catalysis equation named after him. He also came up with the highly used theory of the proton donor along with Lowry. Br nsted theorised that as a hydrogen atom (always found in an acid) is ionized once dissolved in water, it loses its electron and becomes a proton donor. The hydroxide ion, which occurs when an alkali is formed when a substance is dissolved in water is called a proton receiver. This leads to a neutralization reaction where the ions combine creating hydrogen hydroxide, otherwise known as water. The pH scale may be interpreted as "power of hydrogen", and the definition is based on the work of Br nsted and Lowry. Robert Bunsen-a German chemist. His laboratory assistant, Peter Desaga perfected the burner that was later named after Bunsen, which was originally invented by British chemist/physicist Michael Faraday. He also worked on emission spectroscopy of heated elements. Together, he and Gustav Kirchhoff discovered the elements cesium and rubidium. He is considered the founder of modern gasanalytical methods. Melvin Calvin-a chemist most famed for discovering the Calvin cycle (along with Andrew Benson), for which he was awarded the 1961 Nobel Prize in Chemistry. He spent virtually all of his five-decade career at the University of California, Berkeley. Robert Boyle-n Anglo-Irish natural philosopher, chemist, physicist, inventor, and early gentleman scientist, noted for his work in physics and chemistry. He is best known for the formulation of Boyle's law. Although his research and personal philosophy clearly has its roots in the alchemical tradition, he is largely regarded today as the first modern chemist. He is very famous in the science world for being the first scientist that kept accurate experiment logs. Among his works, The Sceptical Chymist is seen as a cornerstone book in the field of chemistry. Marie Curie-aka Madame Curie; November 7, 1867 July 4, 1934) was a Polish-French physicist and chemist. She was a pioneer in the field of radioactivity, the first twice-honored Nobel laureate (and still today the only laureate in two different sciences), and the first female professor at the Sorbonne. Henry Cavendish-a British scientist noted for his discovery of hydrogen or what he called "inflammable air". He described the density of inflammable air, which formed water on combustion, in a 1766 paper "On Factitious Airs". Antoine Lavoisier later reproduced Cavendish's experiment and gave the element its name. John Dalton-an English chemist and physicist, born at Eaglesfield, near Cockermouth in Cumbria. He is best known for his advocacy of the atomic theory and his research into colour blindness (sometimes referred to as Daltonism, in his honour). Around 1790 Dalton seems to have considered taking up law or medicine, but his projects were not met with encouragement from his relatives, and he remained at Kendal until, in the spring of 1793, moving to Manchester. Mainly through John Gough, a blind philosopher to whom he owed much of his scientific knowledge, Dalton was appointed teacher of mathematics and natural philosophy at the Manchester Academy. He remained in that position until the college's relocation to York in 1803, when he became a public and private teacher of mathematics and chemistry. FILIPINO CHEMISTS Daniel Dingel- For more than three decades now, Daniel Dingel has been claiming that his car can run with water as fuel. An article from the Philippine Daily Inquirer said that Dingle built his engine as early as 1969. Dingel built a car reactor that uses electricity from a 12-volt car battery to split the ordinary tap water into hydrogen and oxygen components. The hydrogen can then be used to power the car engine. Dingel said that a number of foreign car companies have expressed interest in his invention. The officials of the Department of Science and Technology (DOST) have dismissed Dingel's water-powered car as a hoax. In return, Dingel accused them of conspiring with oil producing countries. Dingel, however, was the not the only man on earth who is testing water as an alternative fuel. American inventors Rudolf Gunnerman and Stanley Meyer and the researchers of the U.S. Department of Energy's National Renewable Energy Laboratory have been pursuing similar experiments. Dr. Abelardo Aguilar- A Filipino scientist reportedly discovered erythromycin in 1949. He was Dr. Abelardo Aguilar who died in 1993 without being recognized and rewarded for his discovery. Reports said Aguilar discovered the antibiotic from the Aspergillus species of fungi in 1949 and sent samples to Indiana-based pharmaceutical firm Eli Lilly Co. The drug firm allegedly registered the propriety name Iloson for the antibiotic in honor of Iloilo province where Aguilar discovered it. In 1952, Eli Lilly Co. began the commercial distribution of Iloson, which was sold as an alternative to penicillin. Erythromycin, the generic name of Iloson, was reportedly the first successful macrolide antibiotic introduced in the US. Edgardo Vazquez- Edgardo Vazquez won a World Intellectual Property Organization (WIPO) gold medal in 1995 for developing a modular housing system. Such a system called Vazbuilt is reportedly capable of building within weeks a house with prefabricated materials that can withstand typhoons and earthquakes. Ironically, Vasquez is not getting enough support from the Philippine government to propagate his technology, which could help provide shelter to some five million Filipino families without their own homes. Vazquez is the national president of the Filipino Inventors Society. Rudy Lantano Sr.- In 1996, Rudy Lantano Sr.,

Question:I have to fill this out before Monday, and the website our teacher gave us to do so does not exist. I have found most of the answers via google, I was hoping someone could help me with these. 6) __________ decay is the breaking up of a radioactive element, more often than not resulting in the formation of a new nucleus. 7) _________________ is the changing of an atom into another kind of atom that takes place during radioactive decay. 8) In the year __________, Henri Becquerel of __________ discovered radioactivity. 9) Alpha radiation is actually a stream of (positively, negatively) charged particles. 10) Beta radiation is actually a stream of (positively, negatively) charged particles. 11) Whenever an element undergoes (alpha, beta, gamma) decay, it turns into another element with an atomic number two less than before and a mass number four less than before. 12) During (alpha, beta, gamma) decay, a neutron in the nucleus decays into a proton, an electron, and a neutrino. 13) The more stable a nucleus is, the (longer, shorter) its half-life. 17) (Alpha particles, Beta particles, Gamma rays) travel at the speed of light. 18) The term radioactivity was coined by __________. 19) (Alpha particles, Beta particles, Gamma rays) are not affected by a magnetic field because they carry no __________ charge. 20) An alpha particle is actually a nucleus of __________. 21) Beta particles originate in the __________ of the atom. 23) The half-life of a given isotope can be altered by heat, pressure, or some other physical means. True or False.

Answers:6) radioactive 7) ? (decay) 8) 1896, Paris 9) positively 10) negatively 11) alpha 12) beta 13) longer 17) gamma rays 18) Marie Sk odowska Curie 19) gamma rays, electrical 20) Helium (He) 21) nucleus 23) false

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