Angstrom Definition (Physics and Chemistry)

Angstrom Definition (Physics and Chemistry) An angstrom or à ¥ngstrà ¶m  is a unit of length used to measure very small distances. One angstrom is equal to  10−10  m  (one ten-billionth of a  meter  or 0.1  nanometers). Although the unit is recognized world-wide, it is not an International System  (SI) or metric unit.The symbol for angstrom is Ã…, which is a letter in the Swedish alphabet.1 Ã… 10-10 meters. Uses of the Angstrom The diameter of an atom is on the order of 1 angstrom, so the unit is particularly handy when referring to the atomic and ionic radius or size of molecules and spacing between planes of atoms in crystals. The covalent radius of atoms of chlorine, sulfur, and phosphorus are about one angstrom, while the size of a hydrogen atom is about half of an angstrom. The angstrom is used in solid state physics, chemistry, and crystallography. The units is used to cite wavelengths of light, chemical bond length, and the size of microscopic structures using the electron microscope. X-ray wavelengths may be given in angstroms, as these values typically range  1–10 Ã…. Angstrom History The unit is named for Swedish physicist Anders Jonas  Ãƒâ€¦ngstrà ¶m, who used it to produce a chart of the wavelengths of electromagnetic radiation in sunlight in 1868. His use of units made it possible to report the wavelengths of visible light (4000  to  7000  Ãƒâ€¦) without having to use decimals or fractions. The chart and unit became widely used in solar physics, atomic spectroscopy, and other sciences that deal with extremely small structures. Although the angstrom is  10−10  meters, it was precisely defined by its own standard because it is so small. The error in the meter standard was larger than the anstrom unit! The 1907 definition of the angstrom was the wavelength of the red line of cadmium set to be  6438.46963 international à ¥ngstrà ¶ms. In 1960, the standard for the meter was redefined in terms of spectroscopy, finally basing the two units on the same definition. Multiples of the Angstrom Other units based on the angstrom are the micron (104  Ãƒâ€¦) and the millimicron (10 Ã…). These units are used to measure thin film thicknesses and molecular diameters. Writing the Angstrom Symbol Although the symbol for the angstrom is easy to write on paper, some code is needed to produce it using digital media. In older papers, the abbreviation A.U. was sometimes used. Methods of writing the symbol include: Typing the symbol U212B or U00C5 in UnicodeUsing the symbol #8491 or #197 in HTMLUsing the code Aring; in HTML Sources International Bureau of Weights and Measures (2006). The International System of Units (SI) (8th ed.).  p. 127. ISBN 92-822-2213-6.Wells, John C. (2008). Longman Pronunciation Dictionary (3rd ed.). Longman, ISBN 9781405881180.

Types of Nouns and Their Forms, Functions, and Meanings

Types of Nouns and Their Forms, Functions, and Meanings In  The Teachers Grammar Book  (2005), James Williams admits that defining the term  noun  is such a problem that many  grammar  books do not even try to do it. Interestingly, however, one of the founders of  cognitive linguistics  has settled on a familiar definition: In elementary school, I was taught that a noun is the name of a person, place, or thing. In college, I was taught the basic linguistic doctrine that a noun can only be defined in terms of grammatical behavior, conceptual definitions of grammatical classes being impossible. Here, several decades later, I demonstrate the inexorable progress of grammatical theory by claiming that a noun is the name of a thing. -Ronald W. Langacker,  Cognitive Grammar: A Basic Introduction. Oxford University Press, 2008 Professor Langacker notes that his definition of  thing  subsumes people and places as special cases and is not limited to physical entities. Its probably impossible to come up with a universally accepted definition of  a noun. Like many other terms in linguistics, its meaning depends on  context  and use as well as the theoretical biases of the person doing the defining. So rather than wrestle with competing definitions, lets just briefly consider some of the conventional categories of nouns- or more precisely, some of the different ways of grouping nouns in terms of their (often overlapping) forms, functions, and meanings. For additional examples and more detailed explanations of these slippery categories, consult the resources in the Glossary of Grammatical and Rhetorical Terms, covering topics like the possessive case and pluralizing nouns. Abstract Nouns  and  Concrete Nouns An  abstract noun  is a noun that names an idea, quality, or concept (courage  and  freedom, for example). A  concrete noun  is a noun that names a material or tangible object- something recognizable through the senses (such as  chicken  and  egg). But this apparently simple distinction can get tricky. Lobeck and Denham point out that the classification of a noun can change depending on how that noun is used and what its referring to in the real world. When  homework  refers to the idea of schoolwork that will be completed over time, it seems more abstract, but when it refers to an actual document that you submit for a class, it seems concrete. -Navigating English Grammar, 2014. Attributive Nouns An  attributive noun  is a noun that serves as an adjective in front of another nounsuch as nursery  school and birthday  party. Because so many nouns can serve as adjective equivalents, its more accurate to regard  attributive  as a function than as a type. The clustering of nouns in front of another noun is sometimes called  stacking. Collective Nouns A  collective noun  is a noun that refers to a group of individuals- such as  team, committee, and  family. Either a singular or a plural pronoun can stand in for a collective noun, depending on whether the group is regarded as a single unit or as a collection of individuals. (See  Pronoun Agreement.) Common Nouns  and  Proper Nouns A  common noun  is a noun thats not the name of any particular person, place, or thing (for instance,  singer,  river, and  tablet). A  proper noun  is a noun that refers to a specific person, place, or thing (Lady Gaga,  Monongahela River, and  iPad).Most proper nouns are singular, and- with a few exceptions (iPad)- theyre usually written with initial capital letters. When proper nouns are used generically (as in keeping up with the  Joneses or a  xerox  of my term paper), they become, in a sense, common- and in some cases subject to lawsuits. (See  Generification.) Count Nouns  and  Mass Nouns A  count noun  is a noun that has both singular and plural forms- like  dog(s) and  dollar(s). A  mass noun  (also called a  noncount noun) is a noun thats generally used only in the singular and cant be counted- music  and  knowledge, for instance.Some nouns have both countable and non-countable uses, such as the countable dozen  eggs and the non-countable egg  on his face. Denominal Nouns A  denominal noun  is a noun thats formed from another noun, usually by adding a suffix- such as  guitarist  and  spoonful. But dont count on consistency. While a  librarian  usually works in a library and a  seminarian  usually studies in a seminary, a  vegetarian  can show up anywhere. (See  Common Suffixes in English.) Verbal Nouns A  verbal noun  (sometimes called a  gerund) is a noun thats derived from a verb (usually by adding the suffix  -ing) and that exhibits the ordinary properties of a noun- for example, My mother didnt like the idea of my  writing  a book about her.Most contemporary linguists distinguish  verbals  from  deverbals, but not always in precisely the same way.