UNIDAD IV (ACTIVIDAD REALIZADA EN CLASES)

El siguiente trabajo fue realizado en equipo, en compañia de los compañeros, Lenmar Badell, Rafael Riera, Alejandro Castro y Carlos Martinez. Metals Marcadores de definición: A metal is a chemical element that is a good conductor of both electricity and heat and forms cations and ionic bonds with non-metals. In chemistry, a metal (from Greek "μέταλλον" – métallon, "mine"[1]) is an element, compound, or alloy characterized by high electrical conductivity. In a metal, atoms readily lose electrons to form positive ions (cations). Those ions are surrounded by delocalized electrons, which are responsible for the conductivity. The solid thus produced is held by electrostatic interactions between the ions and the electron cloud, which are called metallic bonds.[2] Definition Metals are sometimes described as an arrangement of positive ions surrounded by a sea of delocalized electrons. They are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and non-metals. Metals occupy the bulk of the periodic table, while non-metallic elements can only be found on the right-hand-side of the Periodic Table of the Elements. A diagonal line, drawn from boron (B) to polonium (Po), separates the metals from the nonmetals. Most elements on this line are metalloids, sometimes called semiconductors. This is because these elements exhibit electrical properties common to both conductors and insulators. Elements to the lower left of this division line are called metals, while elements to the upper right of the division line are called nonmetals. An alternative definition of metal refers to the band theory. If one fills the energy bands of a material with available electrons and ends up with a top band partly filled then the material is a metal. This definition opens up the category for metallic polymers and other organic metals, which have been made by researchers and employed in high-tech devices. These synthetic materials often have the characteristic silvery gray reflectiveness (luster) of elemental metals. Using Metals in Astronomy In the specialized usage of astronomy and astrophysics, the term "metal" is often used to refer collectively to all elements other than hydrogen or helium, including substances as chemically non-metallic as neon, fluorine, and oxygen. Nearly all the hydrogen and helium in the Universe was created in Big Bang nucleosynthesis, whereas all the "metals" were produced by nucleosynthesis in stars or supernovae. The Sun and the Milky Way Galaxy are composed of roughly 74% hydrogen, 24% helium, and 2% "metals" (the rest of the elements; atomic numbers 3–118) by mass.[3] The concept of a metal in the usual chemical sense is irrelevant in stars, as the chemical bonds that give elements their properties cannot exist at stellar temperatures. Palabras de definicion: is, are, discribed as, this is, refers to, is a, was. Idea principal del texto: El texto explica la deficion de los metales, se muestran sus elementos y como esta compuesta esa aleacion, asi como tambien el uso quese le puede dar en la astronomia. Marcadores de tiempo: HISTORY OF MOBILE PHONES An evolution of mobile phones Radiophones have a long and varied history going back to Reginald Fessenden's invention and shore-to-ship demonstration of radio telephony, through the Second World War with military use of radio telephony links and civil services in the 1950s. The first mobile telephone call made from a car occurred in St. Louis, Missouri, USA on June 17, 1946, using the Bell System's Mobile Telephone Service, but the system was impractical from what is considered a portable handset today. The equipment weighed 80 pounds (36 kg), and the AT&T service, basically a massive party line, cost $30 USD per month (equal to $337.33 today) plus $.30 to $.40 per local call, equal to $3.37 to $4.5 today. In 1960, the world’s first partly automatic car phone system, Mobile System A (MTA), was launched in Sweden. MTA phones were composed of vacuum tubes and relays, and had a weight of 40 kg. In 1962, a more modern version called Mobile System B (MTB) was launched, which was a push-button telephone, and which used transistors in order to enhance the telephone’s calling capacity and improve its operational reliability. In 1971, the MTD version was launched, opening for several different brands of equipment and gaining commercial success. Martin Cooper, a Motorola researcher and executive is considered to be the inventor of the first practical mobile phone for handheld use in a non-vehicle setting, after a long race against Bell Labs for the first portable mobile phone. Using a modern, if somewhat heavy portable handset, Cooper made the first call on a handheld mobile phone on April 3, 1973 to his rival, Dr. Joel S. Engel of Bell Labs.[7] The first commercially automated cellular network (the 1G generation) was launched in Japan by NTT in 1979, initially in the metropolitan area of Tokyo. Within five years, the NTT network had been expanded to cover the whole population of Japan and became the first nationwide 1G network. In 1981, this was followed by the simultaneous launch of the Nordic Mobile Telephone (NMT) system in Denmark, Finland, Norway and Sweden. In 2001, the first commercial launch of 3G (Third Generation) was again in Japan by NTT DoCoMo on the WCDMA standard. Mobile phones generally obtain power from rechargeable batteries. There are a variety of ways used to charge cell phones, including USB, portable batteries, mains power (using an AC adapter), cigarette lighters (using an adapter), or a dynamo. In 2009, the first wireless charger was released for consumer use. On 17 February 2009, the GSM Association (GSMA), together with 17 mobile phone manufacturers and providers, announced[16] their commitment to implementing a cross-industry standard for a universal charging solution for new mobile phones. In October 2009, the International Telecommunication Union (ITU) announced that it had also embraced the Universal Charging Solution standard - based on the OMTP specifications promoted by the GSMA - as its "energy-efficient one-charger-fits-all new mobile phone solution," and added: "Based on the Micro-USB interface, UCS chargers will also include a 4-star or higher efficiency rating — up to three times more energy-efficient than an unrated charger."[19] In 2009, many mobile phone manufacturers signed a Memorandum of Understanding (MoU), agreeing to make most new data-enabled cell phones marketed in the EU compatible with a common External Power Supply (EPS). In 2006, the People's Republic of China issued a standard for mobile device power supplies (based on a 5V Power Supply with a USB-A receptacle and a detachable cable). The 2006 regulation is flexible regarding the interface on the mobile phone itself, allowing for the use of adapter cables if the mobile device is not equipped with a standard USB connector.[23] The standard was revised in December, 2009 (CCSA YD/T 1591-2006 updated to YD/T 1591-2009).