SUMMARY / RELATED TOPICS

Hydrogen atom

A hydrogen atom is an atom of the chemical element hydrogen. The electrically neutral atom contains a single positively charged proton and a single negatively charged electron bound to the nucleus by the Coulomb force. Atomic hydrogen constitutes about 75% of the baryonic mass of the universe. In everyday life on Earth, isolated hydrogen atoms are rare. Instead, a hydrogen atom tends to combine with other atoms in compounds, or with another hydrogen atom to form ordinary hydrogen gas, H2. "Atomic hydrogen" and "hydrogen atom" in ordinary English use have overlapping, yet distinct, meanings. For example, a water molecule does not contain atomic hydrogen. Atomic spectroscopy shows that there is a discrete infinite set of states in which a hydrogen atom can exist, contrary to the predictions of classical physics. Attempts to develop a theoretical understanding of the states of the hydrogen atom have been important to the history of quantum mechanics, since all other atoms can be understood by knowing in detail about this simplest atomic structure.

The most abundant isotope, hydrogen-1, protium, or light hydrogen, contains no neutrons and is a proton and an electron. Protium is stable and makes up 99.985% of occurring hydrogen atoms. Deuterium contains one proton. Deuterium is stable and makes up 0.0156% of occurring hydrogen and is used in industrial processes like nuclear reactors and Nuclear Magnetic Resonance. Tritium contains two neutrons and one proton and is not stable, decaying with a half-life of 12.32 years. Because of its short half-life, tritium does not exist in nature except in trace amounts. Heavier isotopes of hydrogen are only created artificially in particle accelerators and have half-lives on the order of 10−22 seconds, they are unbound resonances located beyond the neutron drip line. The formulas below are valid for all three isotopes of hydrogen, but different values of the Rydberg constant must be used for each hydrogen isotope. Lone neutral hydrogen atoms are rare under normal conditions. However, neutral hydrogen is common when it is covalently bound to another atom, hydrogen atoms can exist in cationic and anionic forms.

If a neutral hydrogen atom loses its electron, it becomes a cation. The resulting ion, which consists of a proton for the usual isotope, is written as "H+" and sometimes called hydron. Free protons are common in the interstellar medium, solar wind. In the context of aqueous solutions of classical Brønsted–Lowry acids, such as hydrochloric acid, it is hydronium, H3O+, meant. Instead of a literal ionized single hydrogen atom being formed, the acid transfers the hydrogen to H2O, forming H3O+. If instead a hydrogen atom gains a second electron, it becomes an anion; the hydrogen anion is called hydride. The hydrogen atom has special significance in quantum mechanics and quantum field theory as a simple two-body problem physical system which has yielded many simple analytical solutions in closed-form. Experiments by Ernest Rutherford in 1909 showed the structure of the atom to be a dense, positive nucleus with a tenuous negative charge cloud around it; this raised questions about how such a system could be stable.

Classical electromagnetism had shown that any accelerating charge radiates energy, as shown by the Larmor formula. If the electron is assumed to orbit in a perfect circle and radiates energy continuously, the electron would spiral into the nucleus with a fall time of: t fall ≈ a 0 3 4 r 0 2 c ≈ 1.6 ⋅ 10 − 11 s Where a 0 is the Bohr radius and r 0 is the classical electron radius. If this were true, all atoms would collapse, however atoms seem to be stable. Furthermore, the spiral inward would release a smear of electromagnetic frequencies as the orbit got smaller. Instead, atoms were observed to only emit discrete frequencies of radiation; the resolution would lie in the development of quantum mechanics. In 1913, Niels Bohr obtained the energy levels and spectral frequencies of the hydrogen atom after making a number of simple assumptions in order to correct the failed classical model; the assumptions included: Electrons can only be in certain, discrete circular orbits or stationary states, thereby having a discrete set of possible radii and energies.

Electrons do not emit radiation while in one of these stationary states. An electron can lose energy by jumping from one discrete orbital to another. Bohr supposed that the electron's angular momentum is quantized with possible values: L = n ℏ where n = 1, 2, 3... and ℏ is Planck constant over 2 π. He supposed that the centripetal force which keeps the electron in its orbit is provided by the Coulomb force, that energy is conserved. Bohr derived the energy of each orbit of the hydrogen atom to be: E n = − m e e 4

Austinville, Alabama

Austinville is a former town and now a neighborhood within the city of Decatur in Morgan County, United States. It is about 3 miles south from downtown Decatur, centered on the junction of Danville Road and Carridale Street, it was incorporated as a town in 1907 and disincorporated and annexed into the city of Decatur in 1956. Austinville is located at 34.5748149°N 87.0086207°W / 34.5748149. Austinville first appeared on the 1910 U. S. Census three years after it incorporated, it was annexed into Decatur in 1956. See Austinville precinct below. Austinville Precinct was created and first appeared on the 1910 U. S. Census. In 1927, it and the Albany 19th precinct were annexed into the Decatur 1st precinct. In 1960, the Austinville name was attached to a newly-created census division, included the towns of Flint City and Trinity; the division was merged into the Decatur Census Division by 1970

Pennsylvania Impressionism

Pennsylvania Impressionism was an American Impressionist movement of the first half of the 20th century, centered in and around Bucks County, Pennsylvania the town of New Hope. The movement is sometimes referred to as the "New Hope School" or the "Pennsylvania School" of landscape painting. Landscape painter William Langson Lathrop moved to New Hope in 1898, where he founded a summer art school; the mill town was located along the Delaware River, about forty miles from Philadelphia and seventy miles from Manhattan. The area's rolling hills were spectacular, the river, its tributaries, the Delaware Canal were picturesque; the natural beauty attracted the artist Edward Redfield. Redfield painted nature in bold and vibrant colors, was “the pioneer of the realistic painting of winter in America.” His thick layering distinguished him from his contemporaries, he amassed more honors and awards than any other artist in the New Hope Colony. His style is distinguished by its color and usual time of day when painting.

The third major artist to settle in the area was Daniel Garber, who came to New Hope in 1907. Garber applied his paint lightly. An instructor at the Pennsylvania Academy of the Fine Arts in Philadelphia, Garber played a huge part of the new colony. Garber made rain paintings popular; as more artists came to the colony, the artists formed art groups with different ideas. The two main groups were the Modernists. Impressionists were painters who did not stay with the traditional pursuit of painting realistically, but instead explored the possibilities of paint and imagination. An important American Impressionist movement is the Pennsylvania Impressionism; the Pennsylvania Impressionist Movement inspired and influenced major artists such as Walter Schofield, George Sotter and Henry Snell. William Lathrop purchased the Phillips Mill property to use as a venue to hold galleries and exhibitions. However, problems occurred in this venue. Modernist Lloyd Ney submitted a painting of the New Hope canal. Lathrop threatened to reject the painting.

Charles Ramsey, Lloyd Ney’s good friend, was disturbed by this comment and formed the “New Group.” This group rebelled against the traditional impressionists having to inaugurate before the Phillips Mill Exhibition on May 16, 1930. Many years a flood of artists came because of the Garber’s influence for constant rain in Pennsylvania; this group consisted of prominent artists such as Robert A. D. Miller, Peter Keenan, Charles Evans. Other important modernist painters to settle in the area after the initial arrivals were Josef Zenk, Bror Julius Nordfeldt, Swiss-born Joseph Meierhans, Clarence Carter and precisionist, Richard Peter Hoffman of Allentown; these fifteen people made a big mark to for Impressionistic society. There was the “Last Ten.” This group stood out. The Ten consisted of Fern Coppedge and M. Elizabeth Price from New Hope, as well as Nancy Maybin Ferguson, Emma Fordyce MacRae, Eleanor Abrams, Constance Cochrane and Theresa Bernstein; these women influenced many other women to join the Pennsylvania Impressionism Movement.

Similar to the French impressionist movement, this style of art is characterized by an interest in the quality of color and the time of day. This group of artists painted in plein air, or out of doors, to capture the moment. According to James A. Michener Art Museum’s Senior Curator Brian Peterson, “what most characterized Pennsylvania impressionism was not a single, unified style but rather the emergence of many mature, distinctive voices: Daniel Garber's luminous, poetic renditions of the Delaware River. Art historian Thomas C. Folk defines the movement as the Late Pennsylvania School, those artists that "came to prominence in Bucks County after 1915 or after the Armory Show and the Panama-Pacific International Exposition." According to Folk, the three most notable artists in this group were John Fulton Folinsbee, Walter Emerson Baum and George Sotter. One of the artists, Walter Emerson Baum, worked as a teacher and educator and through his founding of the Baum School of Art and the Allentown Art Museum, would serve to expand the influence of the movement out of Bucks County and into Lehigh County Allentown and the Lehigh Valley, where the movement continued to flourish into the 1940s and 1950s.

Today, this group of artists is collectively known as the Baum Circle. Eleanor Abrams Faye Swengel Badura Henry Baker Walter Emerson Baum Theresa Bernstein Rae Sloan Bredin Constance Cochrane Morgan Colt Fern Coppedge Nate Dunn Charles Evans Nancy Maybin Ferguson John Fulton Folinsbee Daniel Garber Frederick Harer L. Birge Harrison John Wells James Peter Keenan William Langson Lathrop Harry Leith-Ross Carl Lindborg Emma Fordyce MacRae Robert A. D. "Rad" Miller Roy Cleveland Nuse Mary Elizabeth Price Herbert Pullinger Edward Redfield Charles Rosen Walter Elmer Schofield Henry B. Snell George Sotter Robert Spencer Louis Stone Richard Wedderspoon Impressionism A