Pauling suggested the idea of electronegativity in 1932 to explain why the strength of a covalent bond between two different atoms (A-B) is stronger than the average of the strengths of the covalent bonds A-A and B-B. His valence bond theory said that this stronger bond between different atoms is caused by the ionic effects to the bonding.
The difference between the electronegativity of atom A and atom B is
where the dissociation energies (that is, the energy needed to break the bond between the atoms), "E", of A-B, A-A and B-B bonds are given in electronvolts, and the factor (eV) is added to make sure the final answer has no unit. With the above formula, we can calculate the difference in elecronegativity between hydrogen and bromine to be 0.73. (dissociation energies: H-Br, 3.79 eV; H-H, 4.52 eV; Br-Br, 2.00 eV)
The above equation only calculates the difference in electronegativity between two elements. To make a scale from the equation, a reference point has to be chosen. Hydrogen was chosen as a reference point because it bonds covalently with many elements. Hydrogen's electronegativity was first fixed at 2.1, but was later changed to 2.20. Another thing that need to be known to make an electronegativity scale is which element is more electronegative than the reference point, which is hydrogen. This is often done with the so-called "chemical intuition": in the above example, hydrogen bromide (H-Br) dissolves in water and breaks into H cation and Br anion. So, it can be assumed that bromine is more electronegative than hydrogen.
To calculate Pauling electronegativity for an element, the data on the dissociation energies of at least two types of covalent bonds created by the element is needed. In 1961, A. L. Allred improved Pauling's original data to include the thermodynamic data that is much more available. These "revised Pauling" electronegativity values are used more often.
Electropositivity is a measure of an element's ability to donate electrons, and form positive ions.
Mainly, this is an attribute of metals. The alkali metals have a single electron in their outer shell and it is easily lost. These metals have low ionization energies.
Linus Pauling
Linus Carl Pauling (February 28, 1901 – August 19, 1994) was an American scientist, peace activist, author and educator. He was one of the most important chemists in history.
Pauling was one of the first scientists to work in quantum chemistry, molecular biology and orthomolecular medicine. He is one of a small group of people to have been given more than one Nobel Prize. He is one of only two people to receive them in different fields (the other person was Marie Curie) and the only person in that group to have been awarded each of his prizes without having to share it with another winner.
Pauling was born and grew-up in Oregon, USA. He went to Oregon Agricultural College and graduated in 1922 with a degree in chemical engineering. Pauling then went to the California Institute of Technology (Caltech), where he received his Ph. D in physical chemistry and mathematical physics in 1925. Two years later, he became an assistant professor at Caltech, and he completed his academic career there after many decades on the faculty. He was a Unitarian.
In 1932, Pauling came up with the idea of electronegativity and made a scale that would help the chemical bonding. Pauling kept doing this work while he also did work on the structure of the atomic .
In 1954, Pauling was given the Nobel Prize in Chemistry for work that he did on the structure of DNA. This work led scientists in the UK to come up with the double helix of DNA.
During the Second World War, Pauling worked on military research and development. But, after the war had ended he became worried about the making and future use of atomic weapons and with the destruction forced on the world by war. Ava Helen Pauling, Linus's wife, was a and in time he came to share her beliefs. Pauling then began to talk about his worries with the effects of nuclear fallout and in 1962, was awarded the Nobel Peace Prize for his work against above ground nuclear testing.
Pauling was also an author and a teacher. His first book, "The Nature of the Chemical Bond" (1939), is still used today. his introductory textbook, "General Chemistry" (1949). Later in life, he became an advocate for greatly increased consumption of vitamin C and other nutrients. He generalized his ideas to define orthomolecular medicine, which is still regarded as unorthodox by conventional medicine. He popularized his concepts, analyses, research and insights in several successful but controversial books, such as "How to Live Longer and Feel Better" in 1986.
Pauling died of prostate cancer on August 19, 1994, at 7:20 PM at home in Big Sur, California. He was 93 years old. A grave marker for him is in Oswego Pioneer Cemetery in Lake Oswego, Oregon.
Pauling received numerous awards and honors during his career. Following are awards and honors he has received.
Strabo
Strabo (; 63/64 BC – ca. AD 24) was a Greek historian, geographer and philosopher.
Strabo was born in a rich family from Pontus which had become part of the Roman Empire a short time before. His mother was Georgian. He studied under several geographers and philosophers. Later he made long travels to Egypt and Kush, among others. It is not known when his "Geography" was written, though comments within the work itself place the finished version within the reign of Emperor Tiberius.
Strabo's "History" is nearly completely lost. Although Strabo quotes it himself, and other classical authors mention that it existed, the only surviving document is a fragment of papyrus now in possession of the University of Milan (renumbered <nowiki>[</nowiki>Papyrus<nowiki>]</nowiki> 46).
Several different dates have been proposed for Strabo's death, but most of them place it shortly after 23.
Strabo is mostly famous for his 17-volume work "Geographica", which presented a descriptive history of people and places from different regions of the world known to his era. It is an important source of information on the ancient world.
Chris Waddle
Chris Waddle is a former football player. He has played for England national team.
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Ray Ozzie
Ray Ozzie (born November 20, 1955) is an American computer programmer. He is the "Chief Software Architect" (the person in charge of programming) at Microsoft.
Ian Ure
Ian Ure is a former football player. He has played for Scotland national team.
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Skating rink
A skating rink may refer to:
Identity theft
Identity theft is a type of fraud that involves using personal details belonging to the victim. This may be a passport, social security card, student pass, credit card etc. A person who has his or her identity stolen can end up owing money when the thief spends the person's money or uses the person's credit.
Identity theft is a serious crime that affects thousands of people.
Sensor
A sensor is a device that measures a physical quantity and converts it into a 'signal' which can be read by an observer or by an instrument. For example, a mercury thermometer converts the measured temperature into the expansion and contraction of a liquid which can be read on a calibrated glass tube. Video cameras and a digital cameras have an image sensor.
There are many different types of sensors. Some are used in everyday objects, and some are separate.
A sensor that detects temperature. Thermal sensors are in many laptops and computers in order to sound an alarm when a certain temperature has been exceeded.
An electronic device used to measure a physical quantity such as pressure or loudness and convert it into an electronic signal of some kind (e.g. a voltage).