Luis Alvarez - A Profile of the Famous Scientist

Luis Alvarez - A Profile of the Famous Scientist Name: Luis Alvarez Born/Died: 1911-1988 Nationality: American (with antecedents in Spain and Cuba) About Luis Alvarez Luis Alvarez is a good example of how an amateur can have a profound impact on the world of paleontology. We put the word amateur is in quotation marks because, before he turned his attention to the extinction of the dinosaurs 65 million years ago, Alvarez was a highly accomplished physicist (in fact, he won the Nobel Prize in Physics in 1968 for his discovery of the resonance states of fundamental particles). He was also a lifelong inventor, and was responsible for (among other things) the Synchrotron, one of the first particle accelerators used to probe the ultimate constituents of matter. Alvarez was also involved in the later stages of the Manhattan Project, which yielded the nuclear bombs dropped on Japan at the end of World War II. In paleontology circles, though, Alvarez is best known for his late 1970s investigation (conducted with his geologist son, Walter) into the K/T Extinction, the then-mysterious event 65 million years ago that killed the dinosaurs, as well as their pterosaur and marine reptile cousins.  Alvarezs working  theory, inspired by his discovery  of a clay boundary in Italy separating geologic strata from the Mesozoic and Cenozoic Eras, was that the impact of a large comet or meteor threw up billions of tons of dust, which circled around the globe, blotted out the sun, and caused global temperatures to plunge and  the earth’s vegetation to wither, with the result that first plant-eating and then meat-eating dinosaurs starved and froze to death. Alvarezs theory, published in 1980,  was treated with intense skepticism for a full decade, but was finally accepted by the majority of scientists after scattered iridium deposits in the vicinity of the Chicxulub meteor crater (in present-day Mexico) could be traced to the impact of a large interstellar object. (The  rare element iridium is more common deeper in the earth than on the surface, and could only have been scattered in the patterns detected  by a tremendous astronomical impact.)   Still, the widespread acceptance of this theory  hasnt prevented scientists from pointing to ancillary causes for the extinction of the dinosaurs, the most likely candidate being the volcanic eruptions triggered when the Indian subcontinent slammed into the underside of Asia at the end of the Cretaceous period.

Ionic vs Covalent Bonds - Understand the Difference

Ionic vs Covalent Bonds - Understand the Difference A molecule or compound is made when two or more atoms form a  chemical bond, linking them together. The two types of bonds are ionic bonds and covalent bonds. The distinction between them has to do with how equally the atoms participating in the bond share their electrons. Ionic Bonds In an ionic bond, one atom essentially donates an electron to stabilize the other atom. In other words, the electron spends most of its time close to the bonded atom.  Atoms that participate in an ionic bond have different electronegativity values from each other. A polar bond is formed by the attraction between oppositely-charged ions.  For example, sodium and chloride form an ionic bond, to make NaCl, or table salt. You can predict an ionic bond will form when two atoms have different electronegativity values and detect an ionic compound by its properties, including a tendency to dissociate into ions in water. Covalent Bonds In a covalent bond, the atoms are bound by shared electrons. In a true covalent bond, the electronegativity values are the same (e.g., H2, O3), although in practice the electronegativity values just need to be close. If the electron is shared equally between the atoms forming a covalent bond, then the bond is said to be nonpolar. Usually, an electron is more attracted to one atom than to another, forming a polar covalent bond. For example, the atoms in water, H2O, are held together by polar covalent bonds. You can predict a covalent bond will form between two nonmetallic atoms. Also, covalent compounds may dissolve in water, but dont dissociate into ions. Ionic vs Covalent Bonds Summary Heres a quick summary of the differences between ionic and covalent bonds, their properties, and how to recognize them: Ionic Bonds Covalent Bonds Description Bond between metal and nonmetal. The nonmetal attracts the electron, so it's like the metal donates its electron to it. Bond between two nonmetals with similar electronegativities. Atoms share electrons in their outer orbitals. Polarity High Low Shape No definite shape Definite shape Melting Point High Low Boiling Point High Low State at Room Temperature Solid Liquid or Gas Examples Sodium chloride (NaCl), Sulfuric Acid (H2SO4 ) Methane (CH4), Hydrochloric acid (HCl) Chemical Species Metal and nometal (remember hydrogen can act either way) Two nonmetals Do you understand? Test your comprehension with this quiz. Key Points The two main types of chemical bonds are ionic and covalent bonds.An ionic bond essentially donates an electron to the other atom participating in the bond, while electrons in a covalent bond are shared equally between the atoms.The only pure covalent bonds occur between identical atoms. Usually, there is some polarity (polar covalent bond) in which the electrons are shared, but spend more time with one atom than the other.Ionic bonds form between a metal and a nonmetal. Covalent bonds form between two nonmetals.